Even though a significant amount of time had passed since I first watched his lectures, I still find him one of the best lecturers for the following reasons: clean and neat representation of the covered topic, passion and complete devotion. Thank you for this!
- Regarding the phenomenon of the balloon getting way smaller than what is expected is with no doubt due to the change of phase from gas to liquid of the air inside the balloon (so PV=nRT doesn't hold). - Regarding the can of the tennis balls I think that when the tennis balls are new the pressure inside them is larger than 1 atm, so, to limit the inevitably small losses from the interior of the balls to the outside the manufacturers make cans with pressurised air (so that the pressure inside the ball is, at least when it's still inside the can, equal to the pressure outside). In conclusion the "pssst" we can hear is air flowing from the can to the outside. Is that right? As always, thanks for publishing these lectures. Very very appreciated.
1st question,you put the ballon🎈 in the liquid nitrogen, the air will become liquid and the ideal gas law doesn’t hold anymore. 2nd question, the pressure inside the van is higher than 1at. Because the pressure inside the tennis ball 🎾 is greater than 1at so that the ball can bounce very well.To keep that overpressure inside the ball the can should also have overpressure.That is also the reason why the ball become useless if you open the can and don’t play that for days.The air inside the ball will come out and it cannot bounce very well. Is that a correct explanation sir?😊
The first qn can be interpreted from ideal gas law itself. V is proportional to T. Since temperature is so small, volume of gas inside the balloon is decreased. The volume approaches 0 at -273°C.
Hello Dr Lewin, I found all of your lectures, very interesting. Here I would like to make an attempt to provide an explaination to the questions you asked at the end of your lecture. 1. Regarding the ballon issue, I think Air contains 77% nitrogen, hence when you put that ballon in Liquid Nitrogen, a great part of the Air inside the ballon get liquified and it reduces the volume much smaller than what we get from the Gas Equation. 2. In the Tennis ball can case , the pressure inside the can is less than outside pressure so that balls dont get moisture. Please let me know whether it is the correct response .
help with ideal gas equation P·V=n·R·T This is a working equation when you have pressure, volume and T but it can be rearranged P=F/S; force divided by surface V=S·L; surface by lenght equals Volume F/S·S·L=n·R·T removing S we get F·L=n·R·T; force times distance is work or energy How can we understand this equation? is F·L the energy of a cyllinder of n moles of gas that expanded a value of L at a temperature T against an external pressure? or this one, as an expression like the other forces, electrostatic, gravity, etc. F=constant·property/distance F=R·n·T/L which depens on the number or particles or molecules of the gas, n temperature, T, but what is L? is L the height of a cyllinder or box which filled with a gas made of n particles (or moles) at a temperature T? with a Force F by unit surface? thanks for your attention
lectures 32 and 33 are the Thermodynamics section. Think you should of asked was "What textbook did you use and chapters I can investigate these topics in?"
Hi Professor. To tell you the truth I did not know in wich Lecture could I put you the following question: Which is the exact difference between homogeneity and isotropy? In some cases it seems to me that one leads to the other. Can you put some examples of homogeneity without isotropy and viceversa? Thank you Doctor!
What do "homogeneity" and "isotropy" mean? (Intermediate) Can you please give me the definitions of homogeneity and isotropy in astronomy terms?This is a good question, because these concepts are a bit subtle. Homogeneous is defined as "the same in all locations" while isotropic means "the same in all directions." Imagine that the whole universe is an infinitely large field with one perfectly symmetrical hill, which you are seated atop. Look around: you see an isotropic universe, since the hill is equally green and equally steep in all directions. But the universe is not homogeneous: it has a hill!These concepts are important because most modern cosmology is based on the "cosmological principle," the assumption that, on large scales, the universe is both homogeneous and isotropic. Studies of large-scale structure in the universe and analysis of the microwave background radiation help confirm that this assumption is justified. Homogeneity is the sameness of things. If you're looking for homogeneityin your wardrobe, you'll want shirts and jeans that all have something similar about them.Homogeneity can also mean that something is the same throughout. Plain yogurt has a homogeneity about it - it's white all the way through and it should be the same texture throughout. On the other hand, yogurt with fruit at the bottom can be described as having heterogeneity - different textures and different colors. The Greek root homo-, means "same," and genoa means "race" or "kind" - so homogeneity is the quality of being "the same kind. i·so·tro·pic (ī′sə-trō′pĭk, -trŏp′ĭk) adj.Identical in all directions; invariant with respect to direction."cosmic microwave background Cosmic microwave background (CMB): Isotropy in the cosmic background Apart from the small fluctuations discussed above (one part in 100,000), the observed cosmic microwave background radiation exhibits a high degree of isotropy, a zeroth order fact that presents both satisfaction and difficulty for a comprehensive theory. On the one hand, it provides a strong justification for the assumption of homogeneity and isotropy that is common to most cosmological models....
Sir you are using °K but in my book it is written not to use degree other Fahrenheit and centigrade. What should I do? Also the molar at STP is 22.7 according to IUPAC convention
Hello sir, if we partially inflate a helium balloon with a known pressure, volume and temperature we can clearly calculate the # of moles. And lets say as the helium balloon rises the pressure reduces and temperature, and the balloon gets larger in that its volume increases. So supposing you now calculate the number of moles in the balloon when it is at a certain height you would find that the number of moles reduced than what it was when it was partially inflated at the ground level. Why is that so?
11:19 T="total time interval for collision". Initial momentum of particle: p={mV}→. Intermediate momentum of particle at t=½T: p⁰={m(0)}=0. Momentum increase through wall due to collision, in 1st ½T: p'={½Mv}→. Momentum value through wall due to restoring force, in 2nd ½T: p"=←{½Mv}. ∆p ="momentum transfer through wall" =←{½Mv} - {½Mv}→ =←{Mv} = ←{2mV}. Final momentum of particle=initial+change: p"'=←{mV}. ∆x="displacement of pressure front through wall" Χ=|∆x|="wall thickness" |--∆x->| {mV}→|🧱🧱| {m0} |---p'->| (wall displacement=dx→) ←{mV}|
Density of wall=ρ=M/{Volume of wall} So, ρ=M/{XA}, where A= "total wall area". Now momentum transfer is: ∆p/T=←(2m/MX)mV². =←(2m/ρX²A)mV². Net force from wall is due to the sum of all the particles that hitting cross sections, each of value "δA": Σ∆p/T=←(A/δA)(2m/ρX²A)mV² =←(2m/ρX²δA)mV² Assume particle diameter D is of the order of D~|dX|=|dx| and it's speed is: dx/T=V=½(M/m)v. So, as v=X/½T: dx/T=V=½(M/m)(X/½T) =(M/m)(X/T) So, D~(M/m)X X~mD/M Net force is now: Σ∆p/T= ←(2m/ρX²δA)mV² ~←(2m/ρ(mD/M)²δA)mV² =←(2XA/MD²δA)M²V² =←(2XA/D²δA)MV² Pressure on wall is ←Net Force / ←Area: P~←(2XA/D²δA)MV²/←A =(2X/D²δA)MV²
D~10⁻¹⁰{m}. 1/D²~10²⁰ {m⁻²} Number of degrees of freedom is 3, so 2N becomes 6N inside the gas, so there is factor ~6N*10²⁰ {m⁻²} in the formula: P~(6N*10²⁰{m⁻²} )(X/A)MV² XM~mD, so this is also: P~(6N*10²⁰{metres⁻²} )(D/A)mV² A=NδA: P~(6*10²⁰{metres⁻²} )(D/δA)mV² δA~¼πD²: P~(6*4/π)*10²⁰{metres⁻²} )(mV²/D) ~7.639*10²⁰{metres⁻²} (mV²/D) ~7.639*10³⁰{metres⁻³} mV²
Walter you are a great physician that's what i did study at school i did never laugh to much and my dream was to go study in usa to be out of the european mod but i cannot take my account and my books on my back even more where to go live and i encounter another problem i m without brain the little baby kidnapped by charlier from belgium and i always have been admirativ in front of your country for what they did make for us but i m deeply convince that my anderson family i will never meet her again
Hi Professor. Regarding CO2 at 30:00 if we keep temperature 20 degree celsius and keep going increase pressure for instance 70-80 atm and then very fast expose CO2 to 1 atm(assumption). By logic and depending on graph gas should pass through first 60 atm of vapour pressure of CO2 then it will go down to 1 atm via blasting(it will speedy avaporate). 1) I mean CO2 between 80-60 atm will stay in liquid phase for very very little of time then it will starts transfer to gas form. 2) Balloon air become liquid in that temperature thats why expected volume is not maching. 3) Can question (At time 52:20) Pressure in the can is higher and dry other wise it shall collapse like experiment. Am i thinking in correct way? Thanks a lot.
Professor, in a phase change from gas to liquids and from liquids to solids, I think there is formation of inter molecular bonds.Why there is energy released when inter molecular bonds are formed? I think I can explain why there is energy needed to break bonds, since they are electromagnetic forces and to break a bond you would need to move the molecules to a higher potential energy state, and then work is needed. But I can't understand why the reverse process happens, and why there is heat produced, from a molecular perspective. If you could explain a little about these topic I would appreciate it a lot! Thank you for your lectures and for your time.
+Family Father Energy is conserved. If you stretch a spring, over a distance x, the work I have done is 0.5k*x^2. k is the spring constant. We call this potential energy (PE) of the spring. If now I release the spring, this PE is released in the form of kinetic energy (energy is conserved). This picture is adequate to see why atoms when heated store PE (think of them as being springs). The original heat energy is released when the atoms go back to their ground states. The PE becomes zero again.
+Lectures by Walter Lewin. They will make you ♥ Physics. Thank you for the response, but is the cooling of a substance that allow atoms to oscillate near the equilibrium point (Like a SHO when there is low mechanical energy on the system) or is the formation of bonds that take heat of the system? In high school and in basic chemistry material on the web it looks like it's implied that the forming of bonds liberate heat, but it makes more sense to me (while I don't know if that's correct and would appreciate to know for sure) that the refrigeration of a gas is what makes the atoms loose kinetic energy and that allows the forces to be stronger, since it would be oscillating near the lowest potential point and, because of the asymmetry of the PE curve (in relation to the distance in which the forces are zero), the molecules/atoms would be more close to each other, resulting in a liquid or solid. When a magnet is let go next to a metal, the PE goes to kinetic that goes to heat when it collapses with the metal, but I think that the heat generated can be explained in a molecular level as the chaotic movement of the metal molecules, caused by the collision, that increases the average kinetic energy of the total metal molecules (temperature). I've never heard a explanation to really why is heat generated when a bond is created, and how it corresponds to a chaotic motion of molecules that spreads to the outside of the system. I may be a little bit confused with the molecular interpretation of heat and also of PE when dealing with gases (It's due to the electromagnetic forces that act between the molecules/atoms, isn't it?), so I don't know if I was able to clearly put out my doubts, but anyway thank you for your answer, and for all your brilliant and inspiring lectures available for everyone and inspiring a lot of people to love physics!
+Family Father Energy is conserved. If you heat matter you put in energy. Thus if you cool it you get that energy back. If you change ice into water you have to add energy. Thus if water becomes ice, energy is released. There are nice demos to show this. Take an undercooled liquid. Thus its temperature is bellow its "freezing" point. Shake it some and all the liquid becomes solid and you can feel with your hand that its now every warm. Energy is released.
(at 5r1:24) the air inside the balloon is mostly nitrogen. so when the balloon is put in liquid nitrogen, the nitrogen part of air in the balloon liquifies resulting in the much lesser volume of the balloon than expected by ideal gas law.
Sir if we take 32gm oxygen gas that it contains N0 molecule. If we take 4gm Helium then it contain N0 molecule. I you take 23 gm of Sodium then it contain N0 atoms of sodium. Here N0 is avagadros number
I think why balloon volume was zero bcoz due to low temperature it's volume become 1/4 as well as atmosphere pressure is also acting on it due to which it v=0 when it was fully inflated with air outside and inside pressure was equal but when u put it in N2 it loose it air
Professor, in the Fire Extinguisher problem, around min 28:40, you get the result 300 atm but the CO2 inside is in fact at 60 atm, so why is the CO2 inside so heavy for such a volume? To get the 60 atm answer 0.2 of the used weight of the CO2 should be used.
I suppose that when you start pressing the gas at 60 atm the gas starts to become liquid and to occupy less space, and finally you get CO2 liquid with 1/5 of the original volume and at 60 atm, so you can put 5 times more liquid than gas if both at 60 atm with 20°C. No sure if that's right.
So at the point of phase change, no matter how much heat you introduce into the system, it will have the same temperature of the melting point, only the rate of molecules going into another phase will change?
Hello Professor We know that the pressure in case of gas is caused by the molecular bombardment with the walls of the container. When one such molecule collides with the wall, does the energy of that molecule decrease?? Let's say gas is contained in a piston cylinder arrangement in equilibrium position . Outside the cylinder the pressure is atmospheric and inside the cylinder the gas molecules are continuously bombarding with the inner surface of the piston to give the piston an upward force against the atmospheric pressure. So with continuous collisions what happens to the energy of gas molecules?? Shouldn't it decrease because of the collisions and hence the pressure exerted by the gas molecules should decrease with the passage of time and the gas would be compressed??
Simrandeep Bahal molecules/atoms always collide in "perfectly elastic" way, because there is no non-conservative force involve during collision. only conservative force (electrostatic force) is involved during molecular collisions.
Professor Lewin, does the balloon contract because the nitrogen and the oxygen present inside the balloon condense when immersed in liquid nitrogen, which leads to a decrease in volume?
Lectures by Walter Lewin. They will make you ♥ Physics. Can you upload your edX videos? I remember you saying some really insightful things like "Faraday's law powers 1/3rd of the global economy" and I can't find them anymore. Can you also upload the other edX materials (e.g. problem sets) somewhere?
+Lectures by Walter Lewin. They will make you ♥ Physics. Sir, Could it be also because air in the balloon is at an elevated pressure, and increasing the pressure will raise the boiling point temperature at which the gas can liquify and since air is a mixture hence its liquification occurs at higher temp than Pure N2 ?
Hello Doctor. I put here my question because it is related to temperature. Because of my professional work in nuclear engineering I know that temperature is one of the most difficult parameters to be measured in an accurate way. You need proper probes to measure the temperature of the MEDIUM you are measuring. So my question is: if in outher space there is no medium between massive bodies, has it any sense to talk about TEMPERATURE OF THE OUTHER SPACE? Sometimes I've read it is near to absolute zero (about -270 ºC). Without medium we cannot think about convection or conduction. So only radiation works and temperature would depend exclusively of the radiation absorbing propreties of the body immesed in outher space.. Am I right? THANK YOU DOCTOR!!
+Jordi GS Temperature of outer space is 3K (black body radiation). A Nobel Prize was awarded for this discovery.. I suggest you google "microwave background radiation".
sir in the case of the nitrogen and balloon the system is the wall of the loon and the air inside it now at normal temperature the walls are stretched but when we dip it inside liquid n2 the walls are also squeezing so it will not follow ideal gas law
Mountain tops are generally colder than surrounding land at sea level because air masses use (in part) their internal thermal energy to "climb" to higher elevations. As a result of trading internal thermal energy for gravitational potential energy, the air mass decreases in temperature. The air expands and does work on its surrounding air. As a result, its surroundings do work on it, to lift it to higher elevations. This isn't the only weather factor that comes in to play, as it would predict a temperature as cold as 180 Kelvin for the top of Mt Everest, which would freeze you solid. Heat transfer with the surrounding land heated by sunlight, will also come in to play
One mole of carbon is exactly 12 grams, isn't it? The entire atomic mass unit scale is based on the mass of 1 mole of carbon being exactly 12 grams, right?
Dear Dr.Lewin, I have been getting vague answers on why constants are used in equations? Could you explain the scientific explanation behind using them? Not every equation has constants as well. I know it is very basic but sometimes the basics bother us :)
I will try to explain using the ideal gas law. We know that P, V, N, and T are the parameters that describe an ideal gas. From the experiments, we find that P and V are inversely proportional when N and T are kept constant, V and T are directly proportional when P and N are kept constant, etc. So one can say (PV)/(NT) always gives you the same number (for example k: Boltzmann constant) as long as you use the same units (for example: SI units) in your calculations. And that number is not always equal to 1. So constants are needed to make the equations numerically correct as well as the units consistent. It is like the following. We know that area area of a circle is proportional to the square of its radius but numerically area is not just equal to radius^2. You need a constant to make it numerically correct. And as you know, that constant is pi. I hope this helps.
For cooking food stem is needed so why people worried about cooking food at high elevation because at high elevation we can generate steam at quite lower temperature ?
*By lowering the pressure on the water you can make water boil at temperatures of only 1-2 degrees Celsius (it's a classic demo in lectures) , but you cannot boil an egg in that water as that boiling water is freezing cold!*
@@dhaval326 It depends on how you are cooking. If you are frying an egg directly on the skillet surface, elevation will not matter nearly as much (if it does at all). If you are depending on boiling water or steam to transfer heat to your food, elevation will matter a lot. If you can only get your boiling water to 80C, it will not cook nearly as fast as it would at 100C. Take a look at product recipes that give high altitude instructions, and notice that what they have in common is dependence on boiling water. Oatmeal, pasta, rice, etc. Compare this to products with recipes that don't involve boiling water, and you will notice this modification isn't included. An example being pre-made dough for home baked pizza crust.
Very nice lecture by Professor. In the experiment at Time 22 min, the water is supposed to be boiling i.e. T=373 , but it looked like it is not boiling fully. so T could be less than 373K so pressure rise was not as expected to be 5.4. This could be the cause of PG not reading expected value. Maybe i am wrong.
Great lecture sir, but i am still confusing regarding the use of either gas laws and Bernoulli's principle for fluid in a particular situation. Pls help
prof lewin, at 11:03, i didn't understood about momentum transfer being proportional to v^2. So could you please give a more 'formal' explanation of it or atleast provide some links which does so ?. Thank you.
I watched at 11:03. I do explain the v^2 cearly; I cannot add to the clarity of my lecture. I suggest you watch it again and LISTEN also to what I said.
@Sarvesh Padav It's the momentum transfer per second that is proportional to v^2, not just the momentum transfer. The explanation is clear on the textbook (Ohanian Physics 2nd edition). The momentum transfer per second is momentum transfer divided by a time interval or simply 2*m*v / t where t is the time needed by a molecule to travel a distance L if it had the average speed v. We know that speed equals distance divided by time or simply v = L / t and solving for time t we gain t = L / v. Now replace that time t into 2*m*v / t and you will see that momentum transfer per second is equal to 2*m*v / (L / v) = 2*m*v^2 / L from which is obvious that momentum transfer per second is proportional to m*v^2 and thus to v^2.
In the Fire Extinguisher experiment, the Pressure P is calculated to be around 300 atm. But as per the phase diagram and the fire department it is said that @ 60 atm in the extinguisher. So what is 300 atm? Is it not the pressure inside it?
As you can see from the phase diagram, at room temperature CO2 starts to become liquid when the pressure is around 60 atm and the pressure stays at 60 atm until all gas is turned into liquid. 300 atm was calculated if CO2 is assumed to stay entirely in gas phase. According to the phase diagram, at 300 atm, CO2 is in liquid phase and ideal gas law does not apply.
Sir, on planet Jupiter(or any gas giants like it), 'g' will also be a function of 'P', since 'g' is a function of the planet's mass and such planets are nothing but balls of gas. Right?
But, the magnitude of Pressure does depend on 'g'. Since, those planets are nothing but ball of gas, the very matter which makes them are compressible and thus makes 'g' vary, unlike on rocky planets such as earth. Again, pressure is responsible for the non-uniform distribution of mass. That's why I stated that.
@@schattopadhyay1901 Those planets aren't exclusively gas phase. It is just that the gaseous layer of the planet is significantly thicker in proportion to the diameter at the visible edge than it is for any terrestrial planet or moon in the solar system. They all have solid rock cores, and a solid outer core. Jupiter in particular has metallic hydrogen in its core. Indeed it is true that the higher value of g on Jupiter makes the atmosphere's pressure and density gradients a lot higher than that of Earth's atmosphere. Gravity is responsible for the variation in atmospheric pressure, and subsequently the non-uniform distribution of the atmospheric mass.
Professor, I have a big doubt. I'll start study Physics next year, I love it, but not every topic (doubts about Electricity) . For example, I don't fully understand Chemistry, It isn't one of my favourite subjects.Can it be a problem? However, I love Maths too.What could you recommend me to be sure about my decision? It would be lovely if you share your early studies' experience. Thanks.
Critical temperature is the highest temperature upto which a gas can be liquified by increasing pressure. It does not mean that the gas cannot exists in liquid form below that temperature.
Sir at 7:43 you calculate volume of gas. Sir you say that you can take any gas and you apply gas law. Sir how we can apply that. Because it is applicable for ideal gas. Sir how it is applicable for any gas like N2and O2. Is all these gas are ideal gases at room temperature
Dear sir, The tennis balls are sealed tightly with air inside with out any leak.Then why they are kept in pressurised cans?. could you please help me in clearing my doubt and concept behind gas filled tennis ball.Please don't ask me to google it😝😜.since no answer in google satisfied me.
sir i get 2mv...part but mv^2 part i dont get. While multiplying the extra "v",you said it is the no. of particles colliding with wall per second. I did not get this part !!!
Actually I didn't get it either in the 1st place , how did the extra "v" came into multiplication but here is my little calculation . Think about a box of length L . assuming each of molecules has an average velocity of v , the molecules starting from the one end of the box and colliding on the other end , it will take them a roundtripping time of 2L/v, so they bounce off the wall v/2L times per sec, each time delivering momentum 2mv, so the wall will pick up momentum from this “gas” at a rate of 2mv multiplied by v/2L per second. So the force from the gas on wall: F = rate of change of momentum =mv^2 /L. An equal opposite force must be supplied from outside to keep the wall at rest.
2mv= total change in momentum F momentum per second F=2mv/t t=distance covered by molecules /average speed of a molecule t =l/v F=2mv×v/l×1/6n 1/6n is the no of molecules moving in one direction F=(1/3l)mv^2 P=F/A P=(1/3V)mv^2
can anyone find the clip where he is describing gas in a vacum? its where he draws a oblong box with a barrier in the middle gas 1 side vacum the other ???
Thanks Professor for such an intricate piece of work.But I have a small doubt.Are the degrees of freedom of a homonuclear diatomic molecule and a heteronuclear diatomic molecule same?
Sir when you did an experiment with balloons by dipping them in liquid nitrogen the volume of the balloon contracted more than what was calculated. Is that because of pressure exerted by liquid nitrogen the balloon.
Avogadro’s number, number of units in one mole of any substance (defined as its molecular weight in grams), equal to 6.022140857 × 1023. tell me how C12 was used?
@@lecturesbywalterlewin.they9259 Carbon-12, the most abundant and stable isotope of Carbon, is the reference isotope for how the amu and mole are defined (or were defined when I first learned it in the early 2000's). Its atom is by defnition is 12 amu in mass, which would mean a "charcoal briquette" of exactly Avogadro's number of pure C12 would be 12 grams. At one point, Oxygen-16 and Hydrogen-1 were both used in a similar manner. Carbon's most common isotope produced experimental results that allowed for a compromise between these two standards.
@@lecturesbywalterlewin.they9259 we can't find Your lectures, is what we' re asking. Btw I bought the book(your book), which you recommended me the other day, i just got it yesterday from Amazon, it seems amazing.
Sir my question is that momentum transfer by one molecule is 2mv. Sir then how you say that momentum transfer per second is propotional to mv2. Sir you say that by multiplying v with MV we can get momentum transfer per second. But how. Sir please explain. Sir according to me sent transfer per second will be 2mv/t
momentum transfer is mv if the particle is absorbed; it's 2 mv if the particle reflects. the higher the speed the less time it takes for the transfer. Thus the momentum transfer per sec (in both cases) is proportional to v^2.
Sir momentum transferred to the wall by one molecule is 2mv. Sir but how the momentum transfer per sencond is mv^2. Sir why you multiply mv with v for momentum transfer. I do not understand the reason
imagine a airplane. airplane goes with velocity V. particles hit airplane surfaces with velocity V but number of molecules hit the airplane propotional with V. then aerodinamic force propotional with V square.
Dear professor: I am studying physical chem in university. I'm confused that compressibility ratio, z of different molecules in different pressure and temperature. I cannot find any video related to this in 8.01 help session or use google. Please help me.
Can anyone tell that what he said the proton + nuetron = atomic mass number and then he said mass of molecule = mass of nuetron × atomic mass number what is the difference between atomic mass number and mass of atom
10:15, i am thinking when you say momentum transfer, you mean the momentum of the particle after hitting the container, which i think is mv, or does momentum transfer have a different meaning?
Professor I have a question. I would be immensely grateful to you if you would answer my question. Following is my question:- Consider the case of real gases or any other material where the internal energy also depends on particle-particle interactions (i.e. in addition to their own kinetic energy). In such a system, is it possible to compress the material without changing its temperature?
When we compress an ideal gas, we can do so in a variety of ways. If we do the compression very slowly so that the gas is always in thermal equilibrium with its environment, then the temperature stays constant and the compression is isothermal.www.physicspages.com/2015/07/09/isothermal-and-adiabatic-compression-of-an-ideal-gas/
In talking and during lectures I always say "X degrees Celcius" and "Y degrees Farentheit" and "Z degrees Kelvin". Just Lik I also say N centimeters an M kilograms. What you write is a different matter and it depends on your taste.
Adiabatic = no heat transfer Isochoric = fixed density, usually constant volume processes as it would be in a closed system Isothermal = constant temperature Isobaric = constant pressure Adiabatic on its own isn't enough to specify the process. The P*V^k = constant relation for adiabatic processes, where k is the specific heat ratio cp/cv, only applies to adiabatic/reversible processes. Also known as adiabatic/isentropic. Think a piston moving slow enough in the cylinder, without friction, that the pressure can equilize at every point along the way. I.e. much slower than the speed of sound in the gas. Joule-Thompson processes are also adiabatic, but they aren't reversible.
If you place a cup of hot water and one of cold water (same amount of water) in your freezer. the hot water will freeze faster. The reason is that hot water has a much higher vapor pressure than cold water thus the hot water will evaporate much faster than the cold water. For every gram water that evaporates 540 cal are needed and that makes the temperature of the hot water go down much faster than that of the cold water. Thus, by the time that the hot water is as cold as the cold water, there is LESS water in the original "hot cup" than there is cold cup. That's why the hot water wins the race. Convection plays no role.
Think about a box filled with N gas molecules with random velocities. Find the pressure on the walls by considering the frequency of collisions with the sides and the resulting momentum transfer to the sides. The only other thing you need to know is that the kinetic energy for a monoatomic gas is E= 3/2 kT =1/2 m v_rms ^2, with v_rms the root mean square velocity of the gas. This is very straightforward to carry out and requires nothing more than 8.01 level mechanics.
Mass number is a "nameplate" mass of the isotope in question. It counts the nucleons (i.e. protons and neutrons) in the nucleus. It doesn't care whether these particles are exactly 1 amu or not. It is always an integer. Atomic mass of an isotope accounts for other nuclear factors that come in to play. Not every nucleon is exactly 1 amu, and not every proton/electron pair is exactly 1 amu either. They are on average in Carbon-12 by definition, but other nuclear factors affect the overall mass as the nucleons form the atom's nucleus. Atomic mass of an element, accounts for the mix of this element's isotopes at their relative abundance percentages as they are found naturally on Earth. Both the isotope atomic mass and the percent abundance are multiplied for each isotope in question, and then added up to get a sum total.
@@purushottamgupta3155 The mole and the gram are not relevant to the definition of atomic mass. That is molar mass. Atomic mass is at the scale of the individual atom. The mole is set up by definition, so that molar mass is the same number as atomic/molecular mass, except in units of grams per mole, instead of amu/(atom or molecule).
you are always genius.. @30 min.. you calculatex pressue for fire extinguisher.. it turned around 300 atm... but fire department told 60 atm... as per calculations 300 should be right... if it has to be 60 atm then volume should be very high..... why is the theoeitically calculated pressure value so different from 60atm.... sorry to disturb... could not find solution.... kindly explain
It was found to be 300 assuming the co2 remained a gas. That's why he could apply the gas law. But as it went liquid after 60 atm, the gas law was not working with a gas now, so it gave the wrong answer.
22.7 Liters/mole is the value at 0C and 1 bar pressure. 22.4 Liters/mole is the value at 0C and 1 atm pressure. His example uses 293 K (i.e. 20 C) and 1 atm pressure. IUPAC changed the definition in 1982 to use the bar ("the metric atmosphere") instead of the atmosphere as the definition of "standard temperature and pressure".
@@carultch *Thank you carultch for your many very thoughtful and very useful comments. Keep it up!* As a thank you note I'd like to send you a signed copy of my book "For the Love of Physics" if you don't have one yet.
Even though a significant amount of time had passed since I first watched his lectures, I still find him one of the best lecturers for the following reasons: clean and neat representation of the covered topic, passion and complete devotion. Thank you for this!
Great to hear!
- Regarding the phenomenon of the balloon getting way smaller than what is expected is with no doubt due to the change of phase from gas to liquid of the air inside the balloon (so PV=nRT doesn't hold).
- Regarding the can of the tennis balls I think that when the tennis balls are new the pressure inside them is larger than 1 atm, so, to limit the inevitably small losses from the interior of the balls to the outside the manufacturers make cans with pressurised air (so that the pressure inside the ball is, at least when it's still inside the can, equal to the pressure outside).
In conclusion the "pssst" we can hear is air flowing from the can to the outside. Is that right?
As always, thanks for publishing these lectures. Very very appreciated.
Thanks 👍
That's what I also thought
Sir , I m very greatful to you
Thank you for nicely explained this topic I was very much confused about this before but now everything clear
:)
1st question,you put the ballon🎈 in the liquid nitrogen, the air will become liquid and the ideal gas law doesn’t hold anymore. 2nd question, the pressure inside the van is higher than 1at. Because the pressure inside the tennis ball 🎾 is greater than 1at so that the ball can bounce very well.To keep that overpressure inside the ball the can should also have overpressure.That is also the reason why the ball become useless if you open the can and don’t play that for days.The air inside the ball will come out and it cannot bounce very well. Is that a correct explanation sir?😊
The first qn can be interpreted from ideal gas law itself. V is proportional to T. Since temperature is so small, volume of gas inside the balloon is decreased. The volume approaches 0 at -273°C.
it would've been so beneficial if could've availed your lecture on thermodynamics too.
Yes.....
Hello Dr Lewin,
I found all of your lectures, very interesting.
Here I would like to make an attempt to provide an explaination to the questions you asked at the end of your lecture.
1. Regarding the ballon issue, I think Air contains 77% nitrogen, hence when you put that ballon in Liquid Nitrogen, a great part of the Air inside the ballon get liquified and it reduces the volume much smaller than what we get from the Gas Equation.
2. In the Tennis ball can case , the pressure inside the can is less than outside pressure so that balls dont get moisture.
Please let me know whether it is the correct response .
I had never attended such a great class on this topic before.
Thanks a lot sir.
It helped me a lot to clear my backlog of Thermodynamics.
you’re my role model, sir. i hope someday i could be as incredibly intelligence as you.
Legend only birth once.
Hey genia where are you studying in
Best physics lectures on TH-cam!
help with ideal gas equation
P·V=n·R·T
This is a working equation when you have pressure, volume and T
but it can be rearranged
P=F/S; force divided by surface
V=S·L; surface by lenght equals Volume
F/S·S·L=n·R·T removing S we get
F·L=n·R·T;
force times distance is work or energy
How can we understand this equation?
is F·L the energy of a cyllinder of n moles of gas that expanded a value of L at a temperature T against an external pressure?
or this one, as an expression like the other forces, electrostatic, gravity, etc. F=constant·property/distance
F=R·n·T/L
which depens on the number or particles or molecules of the gas, n
temperature, T,
but what is L?
is L the height of a cyllinder or box which filled with a gas made of n particles (or moles) at a temperature T? with a Force F by unit surface?
thanks for your attention
Excellent lecture. Huge respect from India.
Sir do you have lectures on Thermodynamics? I cannot find them.
lectures 32 and 33 are the Thermodynamics section. Think you should of asked was "What textbook did you use and chapters I can investigate these topics in?"
Hi Professor.
To tell you the truth I did not know in wich Lecture could I put you the following question:
Which is the exact difference between homogeneity and isotropy? In some cases it seems to me that one leads to the other.
Can you put some examples of homogeneity without isotropy and viceversa?
Thank you Doctor!
What do "homogeneity" and "isotropy" mean? (Intermediate)
Can you please give me the definitions of homogeneity and isotropy in astronomy terms?This is a good question, because these concepts are a bit subtle. Homogeneous is defined as "the same in all locations" while isotropic means "the same in all directions." Imagine that the whole universe is an infinitely large field with one perfectly symmetrical hill, which you are seated atop. Look around: you see an isotropic universe, since the hill is equally green and equally steep in all directions. But the universe is not homogeneous: it has a hill!These concepts are important because most modern cosmology is based on the "cosmological principle," the assumption that, on large scales, the universe is both homogeneous and isotropic. Studies of large-scale structure in the universe and analysis of the microwave background radiation help confirm that this assumption is justified.
Homogeneity is the sameness of things. If you're looking for homogeneityin your wardrobe, you'll want shirts and jeans that all have something similar about them.Homogeneity can also mean that something is the same throughout. Plain yogurt has a homogeneity about it - it's white all the way through and it should be the same texture throughout. On the other hand, yogurt with fruit at the bottom can be described as having heterogeneity - different textures and different colors. The Greek root homo-, means "same," and genoa means "race" or "kind" - so homogeneity is the quality of being "the same kind.
i·so·tro·pic (ī′sə-trō′pĭk, -trŏp′ĭk)
adj.Identical in all directions; invariant with respect to direction."cosmic microwave background
Cosmic microwave background (CMB): Isotropy in the cosmic background
Apart from the small fluctuations discussed above (one part in 100,000), the observed cosmic microwave background radiation exhibits a high degree of isotropy, a zeroth order fact that presents both satisfaction and difficulty for a comprehensive theory. On the one hand, it provides a strong justification for the assumption of homogeneity and isotropy that is common to most cosmological models....
Sir, can you please make a video on " Law on equipartition of gases " .
en.wikipedia.org/wiki/Equipartition_theorem
Hello,very nice lecture by proff,can we find the video with solved problems of this lecture.
By MIT open course
No such video exists.
Sir you are using °K but in my book it is written not to use degree other Fahrenheit and centigrade.
What should I do? Also the molar at STP is 22.7 according to IUPAC convention
do what you like
Love these lectures. They are so entertaining
Hello sir, if we partially inflate a helium balloon with a known pressure, volume and temperature we can clearly calculate the # of moles. And lets say as the helium balloon rises the pressure reduces and temperature, and the balloon gets larger in that its volume increases. So supposing you now calculate the number of moles in the balloon when it is at a certain height you would find that the number of moles reduced than what it was when it was partially inflated at the ground level. Why is that so?
+snipez285 N moles of helium have a mass of 4N grams. That's independent of the pressure.
No.of moles remain constant. Volume changes in such a way that PV/T remains constant, considering the gas to be ideal
11:19 T="total time interval for collision".
Initial momentum of particle:
p={mV}→.
Intermediate momentum of particle at t=½T:
p⁰={m(0)}=0.
Momentum increase through wall due to collision, in 1st ½T:
p'={½Mv}→.
Momentum value through wall due to restoring force, in 2nd ½T:
p"=←{½Mv}.
∆p ="momentum transfer through wall"
=←{½Mv} - {½Mv}→
=←{Mv}
= ←{2mV}.
Final momentum of particle=initial+change:
p"'=←{mV}.
∆x="displacement of pressure front through wall"
Χ=|∆x|="wall thickness"
|--∆x->|
{mV}→|🧱🧱|
{m0} |---p'->| (wall displacement=dx→)
←{mV}|
Density of wall=ρ=M/{Volume of wall}
So, ρ=M/{XA}, where A= "total wall area".
Now momentum transfer is:
∆p/T=←(2m/MX)mV².
=←(2m/ρX²A)mV².
Net force from wall is due to the sum
of all the particles that hitting cross sections, each of value "δA":
Σ∆p/T=←(A/δA)(2m/ρX²A)mV²
=←(2m/ρX²δA)mV²
Assume particle diameter D is of the order of D~|dX|=|dx| and it's speed is:
dx/T=V=½(M/m)v.
So, as v=X/½T:
dx/T=V=½(M/m)(X/½T)
=(M/m)(X/T)
So, D~(M/m)X
X~mD/M
Net force is now:
Σ∆p/T= ←(2m/ρX²δA)mV²
~←(2m/ρ(mD/M)²δA)mV²
=←(2XA/MD²δA)M²V²
=←(2XA/D²δA)MV²
Pressure on wall is ←Net Force / ←Area:
P~←(2XA/D²δA)MV²/←A
=(2X/D²δA)MV²
Number of particles hitting wall=N:
N=A/δA
So, Pressure on wall is
P~(2NX/D²A)MV²
D~10⁻¹⁰{m}.
1/D²~10²⁰ {m⁻²}
Number of degrees of freedom is 3, so 2N becomes 6N inside the gas, so there is factor ~6N*10²⁰ {m⁻²} in the formula:
P~(6N*10²⁰{m⁻²} )(X/A)MV²
XM~mD, so this is also:
P~(6N*10²⁰{metres⁻²} )(D/A)mV²
A=NδA:
P~(6*10²⁰{metres⁻²} )(D/δA)mV²
δA~¼πD²:
P~(6*4/π)*10²⁰{metres⁻²} )(mV²/D)
~7.639*10²⁰{metres⁻²} (mV²/D)
~7.639*10³⁰{metres⁻³} mV²
Walter you are a great physician that's what i did study at school i did never laugh to much and my dream was to go study in usa to be out of the european mod but i cannot take my account and my books on my back even more where to go live and i encounter another problem i m without brain the little baby kidnapped by charlier from belgium and i always have been admirativ in front of your country for what they did make for us but i m deeply convince that my anderson family i will never meet her again
at 7:24 you have written 293 degrees kelvin. but degree is not written with kelvin.
Hi Professor. Regarding CO2 at 30:00 if we keep temperature 20 degree celsius and keep going increase pressure for instance 70-80 atm and then very fast expose CO2 to 1 atm(assumption). By logic and depending on graph gas should pass through first 60 atm of vapour pressure of CO2 then it will go down to 1 atm via blasting(it will speedy avaporate). 1) I mean CO2 between 80-60 atm will stay in liquid phase for very very little of time then it will starts transfer to gas form.
2) Balloon air become liquid in that temperature thats why expected volume is not maching.
3) Can question (At time 52:20) Pressure in the can is higher and dry other wise it shall collapse like experiment.
Am i thinking in correct way? Thanks a lot.
I do not know - I suggest you check google - pressure vs temp.
Professor, in a phase change from gas to liquids and from liquids to solids, I think there is formation of inter molecular bonds.Why there is energy released when inter molecular bonds are formed? I think I can explain why there is energy needed to break bonds, since they are electromagnetic forces and to break a bond you would need to move the molecules to a higher potential energy state, and then work is needed. But I can't understand why the reverse process happens, and why there is heat produced, from a molecular perspective. If you could explain a little about these topic I would appreciate it a lot! Thank you for your lectures and for your time.
+Family Father Energy is conserved. If you stretch a spring, over a distance x, the work I have done is 0.5k*x^2. k is the spring constant. We call this potential energy (PE) of the spring. If now I release the spring, this PE is released in the form of kinetic energy (energy is conserved). This picture is adequate to see why atoms when heated store PE (think of them as being springs). The original heat energy is released when the atoms go back to their ground states. The PE becomes zero again.
+Lectures by Walter Lewin. They will make you ♥ Physics. Thank you for the response, but is the cooling of a substance that allow atoms to oscillate near the equilibrium point (Like a SHO when there is low mechanical energy on the system) or is the formation of bonds that take heat of the system? In high school and in basic chemistry material on the web it looks like it's implied that the forming of bonds liberate heat, but it makes more sense to me (while I don't know if that's correct and would appreciate to know for sure) that the refrigeration of a gas is what makes the atoms loose kinetic energy and that allows the forces to be stronger, since it would be oscillating near the lowest potential point and, because of the asymmetry of the PE curve (in relation to the distance in which the forces are zero), the molecules/atoms would be more close to each other, resulting in a liquid or solid. When a magnet is let go next to a metal, the PE goes to kinetic that goes to heat when it collapses with the metal, but I think that the heat generated can be explained in a molecular level as the chaotic movement of the metal molecules, caused by the collision, that increases the average kinetic energy of the total metal molecules (temperature). I've never heard a explanation to really why is heat generated when a bond is created, and how it corresponds to a chaotic motion of molecules that spreads to the outside of the system. I may be a little bit confused with the molecular interpretation of heat and also of PE when dealing with gases (It's due to the electromagnetic forces that act between the molecules/atoms, isn't it?), so I don't know if I was able to clearly put out my doubts, but anyway thank you for your answer, and for all your brilliant and inspiring lectures available for everyone and inspiring a lot of people to love physics!
+Family Father Energy is conserved. If you heat matter you put in energy. Thus if you cool it you get that energy back. If you change ice into water you have to add energy. Thus if water becomes ice, energy is released. There are nice demos to show this. Take an undercooled liquid. Thus its temperature is bellow its "freezing" point. Shake it some and all the liquid becomes solid and you can feel with your hand that its now every warm. Energy is released.
(at 5r1:24) the air inside the balloon is mostly nitrogen. so when the balloon is put in liquid nitrogen, the nitrogen part of air in the balloon liquifies resulting in the much lesser volume of the balloon than expected by ideal gas law.
:)
The pressure in the tennis balls is larger right?
Yes. The air in the balls should be what makes it bouncy.
Sir if we take 32gm oxygen gas that it contains N0 molecule.
If we take 4gm Helium then it contain N0 molecule.
I you take 23 gm of Sodium then it contain N0 atoms of sodium. Here N0 is avagadros number
google Avogadro's number.
I think why balloon volume was zero bcoz due to low temperature it's volume become 1/4 as well as atmosphere pressure is also acting on it due to which it v=0 when it was fully inflated with air outside and inside pressure was equal but when u put it in N2 it loose it air
Best professor.
hey doc, does any of your lectures cover thermodynamics?
Professor, in the Fire Extinguisher problem, around min 28:40, you get the result 300 atm but the CO2 inside is in fact at 60 atm, so why is the CO2 inside so heavy for such a volume? To get the 60 atm answer 0.2 of the used weight of the CO2 should be used.
I suppose that when you start pressing the gas at 60 atm the gas starts to become liquid and to occupy less space, and finally you get CO2 liquid with 1/5 of the original volume and at 60 atm, so you can put 5 times more liquid than gas if both at 60 atm with 20°C. No sure if that's right.
YES
Thanks Professor.
Hello sir
You are great teacher
So at the point of phase change, no matter how much heat you introduce into the system, it will have the same temperature of the melting point, only the rate of molecules going into another phase will change?
correct
Hello Professor
We know that the pressure in case of gas is caused by the molecular bombardment with the walls of the container. When one such molecule collides with the wall, does the energy of that molecule decrease?? Let's say gas is contained in a piston cylinder arrangement in equilibrium position . Outside the cylinder the pressure is atmospheric and inside the cylinder the gas molecules are continuously bombarding with the inner surface of the piston to give the piston an upward force against the atmospheric pressure. So with continuous collisions what happens to the energy of gas molecules?? Shouldn't it decrease because of the collisions and hence the pressure exerted by the gas molecules should decrease with the passage of time and the gas would be compressed??
use google
Simrandeep Bahal molecules/atoms always collide in "perfectly elastic" way, because there is no non-conservative force involve during collision. only conservative force (electrostatic force) is involved during molecular collisions.
Professor Lewin, does the balloon contract because the nitrogen and the oxygen present inside the balloon condense when immersed in liquid nitrogen, which leads to a decrease in volume?
Castor Gemini Yes that is correct, oxygen becomes liquid at 90 K, the liquid nitrogen that I used was 70 K.
Lectures by Walter Lewin. They will make you ♥ Physics. Thank you, Professor!
Lectures by Walter Lewin. They will make you ♥ Physics. Can you upload your edX videos? I remember you saying some really insightful things like "Faraday's law powers 1/3rd of the global economy" and I can't find them anymore. Can you also upload the other edX materials (e.g. problem sets) somewhere?
+Lectures by Walter Lewin. They will make you ♥ Physics.
Sir, Could it be also because air in the balloon is at an elevated pressure, and increasing the pressure will raise the boiling point temperature at which the gas can liquify and since air is a mixture hence its liquification occurs at higher temp than Pure N2 ?
How many minutes into the lecture?
Is the reason that the balloon gets super small because it is a liquid not a gas?
Hello Doctor. I put here my question because it is related to temperature.
Because of my professional work in nuclear engineering I know that temperature is one of the most difficult parameters to be measured in an accurate way. You need proper probes to measure the temperature of the MEDIUM you are measuring.
So my question is: if in outher space there is no medium between massive bodies, has it any sense to talk about TEMPERATURE OF THE OUTHER SPACE? Sometimes I've read it is near to absolute zero (about -270 ºC).
Without medium we cannot think about convection or conduction. So only radiation works and temperature would depend exclusively of the radiation absorbing propreties of the body immesed in outher space.. Am I right? THANK YOU DOCTOR!!
+Jordi GS Temperature of outer space is 3K (black body radiation). A Nobel Prize was awarded for this discovery.. I suggest you google "microwave background radiation".
I like the way you ask the question . Thanks a lot professor , really you are great.
sir in the case of the nitrogen and balloon the system is the wall of the loon and the air inside it now at normal temperature the walls are stretched but when we dip it inside liquid n2 the walls are also squeezing so it will not follow ideal gas law
Sir why on adding all the mass of electron, proton and neutron of one mole of atoms of an element it differ from atomic mass number in gram?
2 protons + 2 neutrons in a helium nucleus have a lower mass than 2 single protons and 2 single neutrons due to "binding energy".
7:56 Professor, the value of 8.3×293/(1.03×10⁵) is coming out to be approx 0.02365 lit.
Where am I wrong, please help
that is not lit. i guess. it is m cube. 1 lit. = 10e-3 m cube
Sir how was the gas constant, boltzman constant found out?
you measure other variables, then calculate the constant
Hi, I´ve a question, If temperature remains constant indepent of the height then why is it colder on for example Mt. Everest?
>>>>If temperature remains constant indepent of the height>>>> it doesn't - use google
Mountain tops are generally colder than surrounding land at sea level because air masses use (in part) their internal thermal energy to "climb" to higher elevations. As a result of trading internal thermal energy for gravitational potential energy, the air mass decreases in temperature. The air expands and does work on its surrounding air. As a result, its surroundings do work on it, to lift it to higher elevations.
This isn't the only weather factor that comes in to play, as it would predict a temperature as cold as 180 Kelvin for the top of Mt Everest, which would freeze you solid. Heat transfer with the surrounding land heated by sunlight, will also come in to play
what kind of space is there between molecules of gases ? i mean if atoms are not there then what else ?
One mole of carbon is exactly 12 grams, isn't it? The entire atomic mass unit scale is based on the mass of 1 mole of carbon being exactly 12 grams, right?
correct
Dear Dr.Lewin,
I have been getting vague answers on why constants are used in equations? Could you explain the scientific explanation behind using them? Not every equation has constants as well. I know it is very basic but sometimes the basics bother us :)
use google
@@lecturesbywalterlewin.they9259 I found no clear answers in that Professor
I will try to explain using the ideal gas law. We know that P, V, N, and T are the parameters that describe an ideal gas. From the experiments, we find that P and V are inversely proportional when N and T are kept constant, V and T are directly proportional when P and N are kept constant, etc. So one can say (PV)/(NT) always gives you the same number (for example k: Boltzmann constant) as long as you use the same units (for example: SI units) in your calculations. And that number is not always equal to 1. So constants are needed to make the equations numerically correct as well as the units consistent.
It is like the following. We know that area area of a circle is proportional to the square of its radius but numerically area is not just equal to radius^2. You need a constant to make it numerically correct. And as you know, that constant is pi. I hope this helps.
For cooking food stem is needed so why people worried about cooking food at high elevation because at high elevation we can generate steam at quite lower temperature ?
*By lowering the pressure on the water you can make water boil at temperatures of only 1-2 degrees Celsius (it's a classic demo in lectures) , but you cannot boil an egg in that water as that boiling water is freezing cold!*
Lectures by Walter Lewin. They will make you ♥ Physics. Ok sir i got it now thank you very much
@@dhaval326 It depends on how you are cooking. If you are frying an egg directly on the skillet surface, elevation will not matter nearly as much (if it does at all). If you are depending on boiling water or steam to transfer heat to your food, elevation will matter a lot. If you can only get your boiling water to 80C, it will not cook nearly as fast as it would at 100C.
Take a look at product recipes that give high altitude instructions, and notice that what they have in common is dependence on boiling water. Oatmeal, pasta, rice, etc. Compare this to products with recipes that don't involve boiling water, and you will notice this modification isn't included. An example being pre-made dough for home baked pizza crust.
Very nice lecture by Professor.
In the experiment at Time 22 min, the water is supposed to be boiling i.e. T=373 , but it looked like it is not boiling fully. so T could be less than 373K so pressure rise was not as expected to be 5.4. This could be the cause of PG not reading expected value. Maybe i am wrong.
+Prakash Kamath Look again, the water is boiling.
Great lecture sir, but i am still confusing regarding the use of either gas laws and Bernoulli's principle for fluid in a particular situation. Pls help
en.wikipedia.org/wiki/Bernoulli%27s_principle
physics.info/gas-laws/summary.shtml
prof lewin, at 11:03, i didn't understood about momentum transfer being proportional to v^2. So could you please give a more 'formal' explanation of it or atleast provide some links which does so ?. Thank you.
I watched at 11:03. I do explain the v^2 cearly; I cannot add to the clarity of my lecture. I suggest you watch it again and LISTEN also to what I said.
@Sarvesh Padav It's the momentum transfer per second that is proportional to v^2, not just the momentum transfer. The explanation is clear on the textbook (Ohanian Physics 2nd edition). The momentum transfer per second is momentum transfer divided by a time interval or simply 2*m*v / t where t is the time needed by a molecule to travel a distance L if it had the average speed v. We know that speed equals distance divided by time or simply v = L / t and solving for time t we gain t = L / v. Now replace that time t into 2*m*v / t and you will see that momentum transfer per second is equal to 2*m*v / (L / v) = 2*m*v^2 / L from which is obvious that momentum transfer per second is proportional to m*v^2 and thus to v^2.
In the Fire Extinguisher experiment, the Pressure P is calculated to be around 300 atm. But as per the phase diagram and the fire department it is said that @ 60 atm in the extinguisher. So what is 300 atm? Is it not the pressure inside it?
As you can see from the phase diagram, at room temperature CO2 starts to become liquid when the pressure is around 60 atm and the pressure stays at 60 atm until all gas is turned into liquid. 300 atm was calculated if CO2 is assumed to stay entirely in gas phase. According to the phase diagram, at 300 atm, CO2 is in liquid phase and ideal gas law does not apply.
Sir, on planet Jupiter(or any gas giants like it), 'g' will also be a function of 'P', since 'g' is a function of the planet's mass and such planets are nothing but balls of gas. Right?
what is P?
I meant 'Pressure'....sir
Pressure exerted is equal from all directions so it's net force & acceleration should be 0. So g might not depend on P
But, the magnitude of Pressure does depend on 'g'. Since, those planets are nothing but ball of gas, the very matter which makes them are compressible and thus makes 'g' vary, unlike on rocky planets such as earth. Again, pressure is responsible for the non-uniform distribution of mass. That's why I stated that.
@@schattopadhyay1901 Those planets aren't exclusively gas phase. It is just that the gaseous layer of the planet is significantly thicker in proportion to the diameter at the visible edge than it is for any terrestrial planet or moon in the solar system. They all have solid rock cores, and a solid outer core. Jupiter in particular has metallic hydrogen in its core.
Indeed it is true that the higher value of g on Jupiter makes the atmosphere's pressure and density gradients a lot higher than that of Earth's atmosphere. Gravity is responsible for the variation in atmospheric pressure, and subsequently the non-uniform distribution of the atmospheric mass.
I am in 9th class .I am interested in physics
Saying Vikas ,
beleive that Kelvin has nothing to do with degrees so it's just kelvin and not degree kelvin
Sir, from where have you given the problems in the assignment of 8.01????
8.01
Physics
Hans C. Ohanian
2nd edition
W.W. Norton & Company
ISBN 0-393-95748-9
allah will always bless you
Professor, I have a big doubt. I'll start study Physics next year, I love it, but not every topic (doubts about Electricity) . For example, I don't fully understand Chemistry, It isn't one of my favourite subjects.Can it be a problem? However, I love Maths too.What could you recommend me to be sure about my decision? It would be lovely if you share your early studies' experience. Thanks.
I cannot give you any advice as I do not know you. Talk to your teachers.
You can clear your doubt just mail me I am a chemistry faculty
Critical temperature of Nitrogen is-146.9°c then how we have nitrogen at - 196°c
Well, critical temperature of water is 374°C...
You should read the definition of critical point.
Critical temperature is the highest temperature upto which a gas can be liquified by increasing pressure. It does not mean that the gas cannot exists in liquid form below that temperature.
@2:00 Sir Walter Lewin For the Love of Chemistry :)))
Sir at 7:43 you calculate volume of gas. Sir you say that you can take any gas and you apply gas law. Sir how we can apply that. Because it is applicable for ideal gas. Sir how it is applicable for any gas like N2and O2. Is all these gas are ideal gases at room temperature
yes the theory is applicable to O2 and N2. Those are as ideal as they come
Dear sir,
The tennis balls are sealed tightly with air inside with out any leak.Then why they are kept in pressurised cans?. could you please help me in clearing my doubt and concept behind gas filled tennis ball.Please don't ask me to google it😝😜.since no answer in google satisfied me.
took me 10 sec to find the answer in google
Very good lecture Sir 🙏🙏🙏🙏. Thanks
Most welcome
Sir can't understand about the extra velocity you multiplied at @11:11 . Will you please elaborate more?
momentum is a vector. It changes from +mv to - mv.
sir i get 2mv...part but mv^2 part i dont get.
While multiplying the extra "v",you said it is the no. of particles colliding with wall per second. I did not get this part !!!
Yes that's what I said and I also mention Why I multiply by v.
Actually I didn't get it either in the 1st place , how did the extra "v" came into multiplication but here is my little calculation . Think about a box of length L . assuming each of molecules has an average velocity of v , the molecules starting from the one end of the box and colliding on the other end , it will take them a roundtripping time of 2L/v, so they bounce off the wall
v/2L times per sec, each time delivering momentum 2mv, so the
wall will pick up momentum from this “gas” at a rate of 2mv multiplied by v/2L per second.
So the force from the gas on wall:
F = rate of change of momentum =mv^2 /L. An equal opposite force must
be supplied from outside to keep the wall at rest.
2mv= total change in momentum
F momentum per second
F=2mv/t
t=distance covered by molecules /average speed of a molecule
t =l/v
F=2mv×v/l×1/6n
1/6n is the no of molecules moving in one direction
F=(1/3l)mv^2
P=F/A
P=(1/3V)mv^2
can anyone find the clip where he is describing gas in a vacum? its where he draws a oblong box with a barrier in the middle gas 1 side vacum the other ???
I think that the volum of the globes is very small because the plastic cubierta del globo
Thank you sir
I am in 11 from india these are very useful for me
Great!
Thanks Professor for such an intricate piece of work.But I have a small doubt.Are the degrees of freedom of a homonuclear diatomic molecule and a heteronuclear diatomic molecule same?
ask google
Are there any other videos for thermal physics?
Sir we learnt that the volume of 1 mole is 22.4 l but you calculated 24 l so is there a difference
At STP (standard pressure and temperature: aka - 0 degrees C and 1 atm) one mole is 22.4 L - at RTP (room temperature) it is 24 L
Sir,Is pressure exerted by liquid nitrogen from all the sides on the ballon a reason for the change in volume more than expected?
question uncler
Sir when you did an experiment with balloons by dipping them in liquid nitrogen the volume of the balloon contracted more than what was calculated. Is that because of pressure exerted by liquid nitrogen the balloon.
yes liquid!
What is the solution of liquid gas balloons??
Sir have you done thermodynamics(heat transfer and thermal expamsion included) videos ?
nope
@@lecturesbywalterlewin.they9259 Please do make lectures on them sir
He actually did it
@@aakashchakraborty3673 where are those lectures can you pls tell
What is the reason behind defining the Avogadro's number with Carbon 12?
Avogadro’s number, number of units in one mole of any substance (defined as its molecular weight in grams), equal to 6.022140857 × 1023.
tell me how C12 was used?
@@lecturesbywalterlewin.they9259 Carbon-12, the most abundant and stable isotope of Carbon, is the reference isotope for how the amu and mole are defined (or were defined when I first learned it in the early 2000's). Its atom is by defnition is 12 amu in mass, which would mean a "charcoal briquette" of exactly Avogadro's number of pure C12 would be 12 grams. At one point, Oxygen-16 and Hydrogen-1 were both used in a similar manner. Carbon's most common isotope produced experimental results that allowed for a compromise between these two standards.
Where can I find lectures for thermodynamics???
search try MIT OCW or EdX or Coursera
@@lecturesbywalterlewin.they9259 we can't find Your lectures, is what we' re asking. Btw I bought the book(your book), which you recommended me the other day, i just got it yesterday from Amazon, it seems amazing.
@@shatakshisharma5240 which book
Sir, how is it that PV=nRT is independent of mass of the molecule taken, afterall, n is dependent on the mass of the molecule and it's quantity ?
@Lectures by Walter Lewin. They will make you ♥ Physics. yes sir..But doesn't that mean the mass of the substance taken will matter ?
mass does matter. READ MY previous msg
where can I find 8.04 Quantum Physics I
it's on a playlist in my channel
Sir my question is that momentum transfer by one molecule is 2mv.
Sir then how you say that momentum transfer per second is propotional to mv2. Sir you say that by multiplying v with MV we can get momentum transfer per second. But how. Sir please explain. Sir according to me sent transfer per second will be 2mv/t
how many minutes into the lecture?
Lectures by Walter Lewin. They will make you ♥ Physics. Sir at 10:50
momentum transfer is mv if the particle is absorbed; it's 2 mv if the particle reflects. the higher the speed the less time it takes for the transfer. Thus the momentum transfer per sec (in both cases) is proportional to v^2.
does anyone have the full lectures about thermodynamics?
search online - maybe MIT's OCW
Sir momentum transferred to the wall by one molecule is 2mv. Sir but how the momentum transfer per sencond is mv^2. Sir why you multiply mv with v for momentum transfer. I do not understand the reason
how many minutes into the lecture?
imagine a airplane. airplane goes with velocity V. particles hit airplane surfaces with velocity V but number of molecules hit the airplane propotional with V. then aerodinamic force propotional with V square.
@@miko_52niko6 why is this force proportional to v in case of water then?
Dear professor: I am studying physical chem in university. I'm confused that compressibility ratio, z of different molecules in different pressure and temperature. I cannot find any video related to this in 8.01 help session or use google. Please help me.
I did not cover that in 8.01. use google
Can anyone tell that what he said the proton + nuetron = atomic mass number and then he said mass of molecule = mass of nuetron × atomic mass number what is the difference between atomic mass number and mass of atom
do not be lazy - use google
am confused about how the momentum transfer is 2mv, thought it was mv.
how many minutes into the lecture?? *It obviously must be 2 mv is that is what I said.*
10:15, i am thinking when you say momentum transfer, you mean the momentum of the particle after hitting the container, which i think is mv, or does momentum transfer have a different meaning?
50:25 200 people doesn't mean 50% chance of having a birthday. It's actually much higher
Professor I have a question. I would be immensely grateful to you if you would answer my question.
Following is my question:-
Consider the case of real gases or any other material where the
internal energy also depends on particle-particle interactions (i.e. in addition to their own
kinetic energy). In such a system, is it possible to compress the material without changing
its temperature?
When we compress an ideal gas, we can do so in a variety of ways. If we do the compression very slowly so that the gas is always in thermal equilibrium with its environment, then the temperature stays constant and the compression is isothermal.www.physicspages.com/2015/07/09/isothermal-and-adiabatic-compression-of-an-ideal-gas/
Thank you very much for your reply..
However, my question was about real gases, it wasn't about an ideal gas..
real gasses are a pain in the neck
can i ask that kelvin is denoted by degree or not
In talking and during lectures I always say "X degrees Celcius" and "Y degrees Farentheit" and "Z degrees Kelvin". Just Lik I also say N centimeters an M kilograms. What you write is a different matter and it depends on your taste.
hey professor, you said there is diagram below in the notes in the description, but there is no diagram
pdf file below the video thumbnail
@@lecturesbywalterlewin.they9259 Exactly sir, there is no diagram in the PDF file.....
I hve physics wallah but i am watching this because. my college is going on. i am watching pw to prepare for iit
adiabatic, isochoric, isothermal and isobaric processes?
Adiabatic = no heat transfer
Isochoric = fixed density, usually constant volume processes as it would be in a closed system
Isothermal = constant temperature
Isobaric = constant pressure
Adiabatic on its own isn't enough to specify the process. The P*V^k = constant relation for adiabatic processes, where k is the specific heat ratio cp/cv, only applies to adiabatic/reversible processes. Also known as adiabatic/isentropic. Think a piston moving slow enough in the cylinder, without friction, that the pressure can equilize at every point along the way. I.e. much slower than the speed of sound in the gas. Joule-Thompson processes are also adiabatic, but they aren't reversible.
Professor why does hot water freeze faster than cold water?
Dank je! :)
If you place a cup of hot water and one of cold water (same amount of water) in your freezer. the hot water will freeze faster. The reason is that hot water has a much higher vapor pressure than cold water thus the hot water will evaporate much faster than the cold water. For every gram water that evaporates 540 cal are needed and that makes the temperature of the hot water go down much faster than that of the cold water. Thus, by the time that the hot water is as cold as the cold water, there is LESS water in the original "hot cup" than there is cold cup. That's why the hot water wins the race. Convection plays no role.
Physics prof.
knows birthday paradox
Sir where can i find the mathematical derivation for PV=NRT
This law is derived from gas laws and R=PV/nT =8.3 J/K, you can search the derivation on google, you will found the derivation from gas laws
Think about a box filled with N gas molecules with random velocities. Find the pressure on the walls by considering the frequency of collisions with the sides and the resulting momentum transfer to the sides. The only other thing you need to know is that the kinetic energy for a monoatomic gas is E= 3/2 kT =1/2 m v_rms ^2, with v_rms the root mean square velocity of the gas.
This is very straightforward to carry out and requires nothing more than 8.01 level mechanics.
sir, what is the reason for sound on opening the ball container at 51:50?
I hear no sound so I cannot answer.
@@lecturesbywalterlewin.they9259 sir but you only have asked the question in the end of lecture about the reason for sound of gas from container.
@@lecturesbywalterlewin.they9259 sir he is asking about the questions which you gave to think about at the end of lecture.
Prof. You ve spoken 'degrees' kelvin throghout this lecture..
Bhavnao ko samjho
ok shut up
Sir what is differnce between atomic mass number and atomic mass
PLEASE learn how to use google
Mass no =no of Proton +no of neutron
While atomic mass is mass of 1 mole of substance
Mass number is a "nameplate" mass of the isotope in question. It counts the nucleons (i.e. protons and neutrons) in the nucleus. It doesn't care whether these particles are exactly 1 amu or not. It is always an integer.
Atomic mass of an isotope accounts for other nuclear factors that come in to play. Not every nucleon is exactly 1 amu, and not every proton/electron pair is exactly 1 amu either. They are on average in Carbon-12 by definition, but other nuclear factors affect the overall mass as the nucleons form the atom's nucleus.
Atomic mass of an element, accounts for the mix of this element's isotopes at their relative abundance percentages as they are found naturally on Earth. Both the isotope atomic mass and the percent abundance are multiplied for each isotope in question, and then added up to get a sum total.
@@purushottamgupta3155 The mole and the gram are not relevant to the definition of atomic mass. That is molar mass. Atomic mass is at the scale of the individual atom.
The mole is set up by definition, so that molar mass is the same number as atomic/molecular mass, except in units of grams per mole, instead of amu/(atom or molecule).
7:10 There again Professor..you ACTUALLY wrote 'degrees Kelvin' . Just 293 Kelvin..I guess
It's probably a matter of habit. Calling all units of temperature a degree in some form or another.
It´s not easy to follow the logical ideas due to its profoundness
you are always genius.. @30 min.. you calculatex pressue for fire extinguisher.. it turned around 300 atm... but fire department told 60 atm... as per calculations 300 should be right... if it has to be 60 atm then volume should be very high..... why is the theoeitically calculated pressure value so different from 60atm.... sorry to disturb... could not find solution....
kindly explain
use google
It was found to be 300 assuming the co2 remained a gas. That's why he could apply the gas law. But as it went liquid after 60 atm, the gas law was not working with a gas now, so it gave the wrong answer.
Dear Professor, 1 atmosphere is 1.013 x 10^5, not 1.03 x 10^5
8:15 Isn't it 22.7 liters
22.7 Liters/mole is the value at 0C and 1 bar pressure.
22.4 Liters/mole is the value at 0C and 1 atm pressure.
His example uses 293 K (i.e. 20 C) and 1 atm pressure.
IUPAC changed the definition in 1982 to use the bar ("the metric atmosphere") instead of the atmosphere as the definition of "standard temperature and pressure".
@@carultch *Thank you carultch for your many very thoughtful and very useful comments. Keep it up!* As a thank you note I'd like to send you a signed copy of my book "For the Love of Physics" if you don't have one yet.
Hi Doctor! Where can i find the first law of thermodynamics?
+Roy Velazquez on the web
Thanks!
at 13:18 you said 1350 or 3050 ??