In the name of SCIENCE, these Lectures must be treasured & DIGITALLY PRESERVED for future generations. There will never be another Feynman, there will never be another Hawking or Sagan. And there will NEVER be another WALTER LEWIN!
After a long night of physics homework, I like to sit down and relax by watching Prof. Lewin videos. Thank you so much for providing all of this free information. There is no greater pleasure to want to learn about orbital motion, or any subject in physics, and then find a video like this.
8.01x Lecture 14 0:00 escape velocity 4:30 Orbital velocity (Example: Shuttle + the moon + earth, jupiter + Sputnik 4/10/1957) => interesting result: v Is independent on the mass 11:55 interesting result from the equation of energy E=1/2U= -KE 13:40 Power 20:10 Heat energy 23:19 Lecture Notes, Energy and Power Consumption 28:30 various form of E 33:55 acid battery 48:00 last ex+ question Give my thanks to Pro. Walter Lewin
@@lecturesbywalterlewin.they9259 Thanks Teacher, the book Physics - Ohanian now is not available for us to find, so i can not solve all the problems which is in this book. Can you help us.
@@thienthanhtranoan6723 Ofcoz I do have a copy of the Ohanian that I used in 1999 but I see no way I can help. Many problems in my assignments simply mention "problem xxx in Ohanian, page yyy". However, when you view the solutions you can guess very often what the problem was about.
The definition of the viral theorem at 11:55 is very ad hoc. Even though it is absolutely correct, I feel like the deepness of this result is not well articulated, but perhaps that is to be expected for an introductory course.
Giving these lecture out for free is a great act of generosity.Knowlege is power and access to knowledge is of paramount importance in making the playing field for all players equal.We need more professor Lewins
Dear Prof. Lewin, thank you for making your lectures available to all of us. You are incredibly talented in highlighting the beauty of Physics! Thanks again!
It makes him look more human. Because to me, alot of teachers (cant say abt professors, im in hs) just seem like robots burnt out and trying to get through the day while hating their job. Meanwhile Sir Walter Lewin's enthusiasm is genuinely infectious and i guess jokes naturally come as a byproduct.
I played with that ball many times in my chidhood.. It is having a circuit inside which blinks the light when bounced or shaked and then turns off.It's having a tiny mercury cell in it.
Mr Walter Lewin, I'm studying Engineering and Management in Germany. At first i would like to say: You're an incredible teacher! You make PHYSICS easy! Thank you very much for your lectures! They're amazing and also save my life in physics at the University. I saw in your lecture notes and assignments that you have a Guide Book. I would like to know, if possible, what book you follow in this course? Thanks for your help. Best regards, Humberto
+Humberto Carpes 8.01 Physics Hans C. Ohanian 2nd edition W.W. Norton & Company ISBN 0-393-95748-9 8.02 Physics for Scientists & Engineers by Douglas C. Giancoli. Prentice Hall ISBN 0-13-021517-1 8.03 Electromagnetic Vibrations, Waves and Radiation by Bekefi and Barrett. The MIT Press ISBN 0-262-52047-8
Hello professor, Regarding the ball, is the blinking because of the vibration of a spring in the ball after the bounce (vibration might cause the blinking - like a momentary switch)
Regarding last question: When we release the ball from height h above the ground, the potential energy starts to convert into kinetic energy and by the time ball reaches ground all the potential energy is converted into kinetic energy(ignoring air drag) and now ground is stopping its motion and hence some of the kinetic energy during impact time converts into heat energy in ground and in ball as well and so inside the ball there is heat energy and jiggly motion of an atoms, and the mechanism of ball’s light is such that it converts this heat energy into an electric energy to light the bulb.
For others who are confused @ 17:27 like me... Friction is ALWAYS opposite to the direction of motion. But in the bicycle example, friction is acting along. Also, kinetic friction is constant, as the cyclist's weight is not changing, so ideally, if it was friction from Lec-8 which was acting, then the cyclist wouldn't be able to accelerate. And the tyres would be scratching the road as it passes by causing the friction to be in opposite direction !! So i guess the choice of word "Friction" is misleading here. It's simply a push by the ground in reaction to the push by the wheel !! Not friction from Lec-8
when an object *slips* then the friction is always opposite to direction of motion and heat is produced. Do not confuse that with an rolling object in pure roll condition; the frictional force is then not slipping and this frictional force can speed up an object (increase its rotation rate) when it is rolling down an incline - (no heat is produced)
@@VickysTuition There are 2 types of friction, static & kinetic. If tyre overcomes static (doesn't slip on surface, object starts to move forward), kinetic friction causes bike to move forward through pure roll of the tyres.
Grav PE is defined as ZERO at infinity. Thus at any finite distance r the Grav PE is NEGATIVE. If the object arrives at infinity with zero KE, then both KE and PE are zero. Energy is conserved thus when the object leaves Earth the sum of PE and KE must also be ZERO.
Hi professor. What did you mean when you said that you wanted to make an object escape at 0 velocity in the infinity? I understood that gravitational potential energy at infinity is 0 but didn't understand about the case of kinetic energy with which any object is sent to escape the earth is also 0!! ?
+Ganesh Budhathoki I can see why you are confused. For when the object reaches infinity with zero speed, both KE and PE are zero. Thus the amount of KE that I have to give an object to make it with zero KE to infinity is +mMG/r if I start at location r from the center of mass M. That is the minimum KE to escape to infinity - if I give it less KE it will not make it to infinity and if I give it more KE it will reach infinity with some residue KE. I hope this is clear now.
@@lecturesbywalterlewin.they9259 Sir, if the total energy is zero at infinity then where will the energy go? How the law of conservation of energy is obeyed in this case?
@@lecturesbywalterlewin.they9259 But mechanical energy should be conserved then how could be 0 at infinity? Please don't be offend with me:( I am a poor boy.
@@mukulbelwal yes you are right - sorry - the total energy is then zero all the way from Earth to inifnity. -MmG/r + 0.5mV^2 = 0 for any r>R, R is the radius of the Earth.
16:52 The Bicycle example; If Fnet(push force by legs & reaction by pedal) = 0 why isn't the pedal stationary; If Fnet = 0 , why is there a force left by pedal that pushes chain; If F friction by road = F push by tyre why is bike still moving; F kinetic means That the external force exerted must be greater than friction ; and finally u said wheels wants to rotate because your pedaling; I am totally confused; Please explain me Guru(Sir).
Sir, In the Bike example you said " I push on the pedals and the pedals push back on me, action equals to minus reaction and therefore there is no net force on the bike" but the forces are acting on the different bodies and if we consider free body diagram of the pedal, the is force which pedal exerts on you and the force which chain exerts on the pedal, so to keep it moving with constant velocity they cancel out. Is it correct?
Hi Dr Lewin, I did some research on the mechanism of the ball experiment that you did at the end of this video, I wonder if the ball blinks because after it collides with the floor, the spring inside the ball gets compressed, thus the gravitational potential energy is converted into spring potential energy. After it bounces up, the spring started oscillating. It takes a period of time for the spring to stop the oscillating ( to transfer the spring potential energy into electricity which lights the electronics inside). Thus, it would blink after bouncing up. I am not sure if my reasoning is legit. Please help me with that. Thank you! I really enjoy your lectures especially the demos!!
Good hypothesis but for a spring to be compressed and store the energy it requires a orientation where the loops of the spring are aligned vertically to the floor when it collides so you would expect it to sometimes blink and sometimes not blink depending on its orientation when it hit the floor but 3 springs aligned 90 degrees to each other may work regardless of orientation.
I thought about this too. However, if that's the case, then at the oscillation of spring would've slowed down to a stop instead of instantly switched off.
Sir, I am a 10th Class Student and I watch your videos regularly. For the last question, even I had a toy like that and that toy has an electric circuit in it with cells. So there is no extra energy produced but the electrical energy converts to light energy once circuit is triggered. Love from India 🇮🇳🇮🇳
There might be an open circuit inside the blinky ball that is completed by an extended spring. When the ball hits the ground, some energy is transferred to the spring and it starts to oscillate, periodically completing the circuit as it extends and compresses. As the spring looses energy due to friction it no longer has enough oomph to complete the circuit and the ball stops blinking.
Professor Lewin , You say that Power = Force * Velocity . But force results in acceleration which results in increase in velocity . So , what velocity do you have to plugin ?
Sir I think in this there is an oscillating thing(spring) associated with the ball.The moment when ball hits the ground it may have acquire energy to oscillate .. and periodically contact with battery and hence lightning takes place as we see..!! Is above arguement is valid for this process or not?
thank you; what does SSR stand for? The Chernobyl disaster was caused by a nuclear accident that occurred on Saturday 26 April 1986, at the No. 4 reactor in the Chernobyl Nuclear Power Plant, near the city of Pripyat in the north of the Ukrainian SSR.
Here is the anwer to the last question th-cam.com/video/YGpXjzC1B0M/w-d-xo.html The ball contains a spring or springs which starts oscillating when given suitable force to ball ,which causes led to flash for some time
Hello Sir, At 47:37 minutes in the lecture when the ball glows or is blinking , is it due to the mechanical energy being converted to electrical energy , like when the ball touches the ground there is some kind of spring in the ball ..that and with a battery the mechanical energy gets converted to electrical ? And does how much time the ball blinks depend on the height from which it was thrown ..like if I throw the ball from a building or something would it glow or blink for a larger period of time as compared to while I throw in when on the ground?
Great lecture. Can I will your permission share it? About the energy problem, I don't think is a tecnical problem, maybe the size of France to be full with solar pannels i too mach, but it is not if that are it will be in Sahara desert. Using all the deserts in the world, as solar power plant + using energy in a more efficient way (like California did recently), we could really resolve the energy problem. But that's not what the problem is. The probles is that most of the politicians all around the world don't want to resolve energy or enviroment problem, and now for our missfortune they are even more ignorants than before, and even don't recognize that we have these problems. Just to supstain my argument, in the time that this lecture was held, in my country parlament, half of them were doctors in science, and even 2 of them had their mathematic theorem recognised by Paris Institute of Technology (Even the President was a renown professor in physics, and his son worked in NASA(I'm not updated)). Todays in 140 members of the parlament just one is a doctor in science (political science!!!), and they are ruining this country.
It is sad to think that solar energy is still expensive nowdays. The Sun is almost a unlimited source of energy to all mankind! Thank you Sir for all your lectures that are keeping me motivated to get my degree on physics!!
Where can we find the explanation for the blinking Ball? I‘m too curious now, my assumption would be that the compression of the Ball plays a role in it
Dear Prof. Walter Lewin, Regarding the brain teaser, may be a coil inside the moment that bounce creates acceleration and power ups the coil. Is it something like this ?
+Lectures by Walter Lewin. They will make you ♥ Physics. well broadly speaking, the fall, you, the food, sun, go back to 'big bang' nd beyond that probably.
Dear Dr.Lewin, If we could put AT REST a mass 400 km from the Earth as the ISS, would it begin to orbit spontaneously? Would it fall on Earth after a few spiiral rounds? Is it necessary an initial impulse to orbit correctly? Is it possible to determine this impulse? Is there any distance from the Earth's so that the orbit began to occur in an spontaneous way? THANK YOU!!
+Jordi GS If you released an object from the ISS which is at rest relative to the ISS then it will orbit the Earth in the same orbit as the ISS. If you throw an object from the ISS in the opposite direction of which ISS is moving and if its speed relative to the ISS is approx 8 km/s then the object has zero speed (it stands still) and it will radially fall to Earth.
@@pratikshinde2121 when the ball hits the floor (or when you bang it on the table) a switch is activated which will drive the current for a fixed amount of time.
accelerometer and battery inside - if te acceleromter measures anything very strong the lights flash they do not generate energy from the impact - that might hteoretically be possible but it’s impractical and expensive you usually just have a battery that lasts very long
Excellent lecture Sir. Thanks. Can you please make two videos on quantum mechanics and theory of relativity covering conclusion to best of knowledge gained so far? Regards 🙏🙏🙏🙏🙏🙏🙏
question: if a rocket is fired up at a speed less than escape velocity, in order to reach a stable orbit, is there some angle to the vertical that must be exceeded upon liftoff? for example if it goes straight up it will obviously come back down. I imagine there would be some Theta that must be exceeded in order for there to be enough tangential motion, and this would depend on the velocity and also would be very difficult to calculate.
all rockets that put a satellite in Earth Orbit start going up vertically then gradualy change that angle to optimize fuel consumption. Also watch my lecture on Kepler Oribits. I have a Physics Problem in which I address that issue.
@@lecturesbywalterlewin.they9259 ah I should've realized to wait until I saw that lecture before asking. sorry for wasting your time!! and thanks for taking the time to reply, it means a lot. stay well ❤
Its not clear how the switch turns on in order for the bulb to emit light. but the energy comes from the moving motion of the ball. the total gerenerated due to the motion of the ball depends on the gravitational constant and the mass of the ball if the consider the work done to be the dot product of force and velocity(w=F.v).
Sir,How is it possible reaching infinity at zero speed as once you give the object an uniform velocity then it maintains it.How could velocity go to zero.Please correct me if i am wrong.
I did respond earlier. It did not get through. If an object has the escape velocity at distance R from the center of a mass M, its speed will decrease all the time as it always experiences the gravitational pull from M. It will take infinitely long to reach "infinity". But it would then get there with speed zero. Infinity is a difficult concept. It has only mathematical meaning. If you calculated the "escape" speed the object would need to reach a distance of 100 million light years, you would find the same value (at least the first 9 digits would be the same) for that speed. That's not so difficult to grasp.
Sir I think that there is a potential energy mgh when we throw the ball and then at the moment it hits the ground that gravitational potential energy turns into kinetic energy and a potential energy which squeezes the ball when it hit the ground. Then this squeezing potential energy turns into electrical energy which make a light bulb (which is programmed to blink) blink. Is it right?
maybe LED is situated in a group of -ve springs with some space between them and +ve terminal of led is already attached to the battery so when ball collide with floor then system becomes unstable and LED moves back and forth and circuit will start switching between on and off. but i don't know why duration between two flash of lights is looks like so uniform?
sir for power we have two formula. is dw/dt used for power increased or decreased of system in some amount of time. and f*v*cos(theta) for instantaneous increment or decrement of power for a system?
My answer for brain teaser... As the ball hits the ground the gravity does the postive work on the ball....and when it comes back to u it will light up till the rate of the change of the work provides sufficient amount of power to light up that bulb. Sir Please let me know ... Am i thinking in right direction?
Sir, can we say that if we intake more calories than required, body increases its surface area (which is proportional to size) to increase the heat rejection to maintain the temperature?
prof can u give me data how u calculated ur daily energy consumption and how u calculated tht this is equivalent to having 100 workers working continuous for 12 hrs?
Lectures by Walter Lewin. They will make you ♥ Physics. I believe his question is that if the ball uses gravitational potential energy to power the led’s than the mechanical energy of the ball decreases because some of it is converted into light energy which leaves the ball so it will not reach the initial height it started at because mgh is now smaller than it was initially and is the light energy radiated a significant fraction of the gravitational potential energy to decrease its height by a measurable amount.
Dear Professor.. I want to ask you said that the force of friction(F,fr)is acted on the direction of your force forward?Isnt friction (F,fr) acing opposite to the force(F,WL) .. Thank you
Ohh now I know professor.. After im thinking for a minute...The rotation of the wheel is clockwide which is to the left ,so must be the friction acted is to the opposite of the rotatio of the wheel...Ohh Poor me...
we know T=2piR/v(orbital) You said that since we know the time period we can easily calculate 'R' and 'v'.How come we can calculate both v and r from a single equation. Also if we use second relationship in terms of mass we dont have mass of earth and radius. Then how come at the time of sputnik did they calculate 'R' and 'v'
looks like i got it wrong may we you meant that we dont know the mass of sputnik. Kindly correct me if I am wrong.before launching of sputnik we knew the mass of earth and calculated it by using f=GMm/r^2 .
Concerning the brain teaser, I don't understand how a battery can be turned on (a switch) just by hitting the ground (is there a special mechanism) and why it keeps blinking just for a while? Are we talking about a capacitor that is charging while you are holding the ball and discharge, immediately after touching the ground, into a light-bulb allowing it to blink momentarily until the voltage across the capacitor come to a value (a threshold) and than stop. THANK YOU SO MUCH FOR YOUR HELP! Sir WL
Here is my try on the brain teaser. When the ball hits the surface, there is heat generated. Maybe there is a detector which detects this sudden change in heat and responds to it by blinking. Afterwards, the heat radiates out and the ball comes back to nearly it's initial temperature?
my uncle worked at PPPL. i heard all about fusion: by 2000, no more petrol, a thermos of water etc etc etc. yada yada yada. i truly believed it, but i'm still waiting... i did get inside the tokamak, tho when it was down, walked about, which was pretty cool. that too is long gone. no idea what they are doing at pppl these days. i guess still hammering away at it.
since the conservation of energy, energy is conserved, noe destroyed neither created. Is there a limit amount of energy in the entire universe? An approximation?
thats to do with biology, i think lactic acid buildup or something, but in terms of physics, no energy is transferred over the duration you are holding the object up for. Pain or effort =/= transferring energy
five 505 that’s because only your muscles are doing the internal work,they contract and expand repeatedly,that’s why they hurt,the work is being done internally not externally as the object isn’t experiencing any work.
near Earth where grav acc is constant mgh is fine. At large distances we have to do better and we define that PE is zero at infinity. Then PE at distance r is -MmG/r I cover this in my lectures
Is there an optimal angle for take off? ..and if so how is this calculated? Pretty much as soon as any rocket "clears the tower" it goes into a roll procedure and angled ascent as quickly as possible.
The first 17 minutes or so--you talk about the the velocity, but don't mention the angle of ascent. As soon as any rocket clears the tower it "rolls" and ascends with a marked angle to the ground. I saw the shuttle lift off, and I expected it to take off straight, but it takes off at an angle off about 25-30deg away from perpendicular after about 10 seconds after lift-off. I imagine there must be a pretty strong reason why they do this (gaining altitude and angular velocity) but surely this would mean that the vehicle must pass through more of the dense lower atmosphere, and this would affect the required escape velocity.
I have not heard yet from Jeff but I have thought about this a bit. When a satellite gets into Earth orbit, it's velocity (about 8 km/s) must be tangential to a near circular orbit. ISS and the Shuttle used to be about 200 miles above the Earth surface. Suppose you go straight out of the atmosphere along the vertical direction then you arrive at 200 miles with a radial velocity but that is NOT what you need. You must end up with a velocity which is 90 degrees away from radial. Thus the fact that the shuttle changes direction soon after launch is probably a matter of fuel economy. Leveling off early on in the launch is more fuel-efficient than first going vertically up to 200 miles with a velocity radially outwards and then changing the direction of motion by 90 degrees. By doing that you would also not stay at 200 miles but you would end up at a much larger distance form Earth. Thus you MUST level off (change direction) sooner to end up in near circular orbit about 200 miles up.
Here is the answer from Professor Hoffman: It is correct that getting above the dense lower atmosphere is important, but there is always a compromise between getting high quickly and starting to accelerate horizontally to eventual orbital velocity of ~18,000 mph. Going straight up is extremely inefficient for a rocket. This is referred to as “gravity loss”. It has to be balanced against atmospheric drag loss. The most efficient way to transition from going straight up out of the launch tower and getting into a horizontal trajectory is called a “gravity turn”. You use the rocket’s steering to start tipping the rocket just a small bit, then gravity pulls it over the rest of the way, so that the rocket thrust can continually be applied parallel to the direction of motion. Any rocket thrust applied sideways to turn the rocket, since it is perpendicular to the direction of motion, will not increase the energy of the rocket. That is why gravity turns are the most efficient. Another consideration is that while carrying out the gravity turn, the rocket gets into the plane of its desired orbit. The sooner this is done (i.e. at the lowest velocity possible) the less cost there is to establish a new orbital plane.
sir I have a question.. as we know that escape velocity=√2gr then from here can we say that from centre of the earth the escape velocity is 0... i mean this feels quite non intuitive..
oh wait... there the term r, literally means radius and not the distance, so we cannot have an object with radius 0m, that makes the whole question wrong..... Am I right sir ?
I have the same plate.They are beautiful (and there's something unique about the orange color-you can match it until you can't tell the difference, but the non-uranium color won't 'feel' the same.) I ate from it for 20+ years. I emailed the safety question to Theodore Gray who makes books on the elements of the periodic table. He said there is a risk from the plate, but it is not the radiation, it's that uranium is a heavy metal. So its about the same risk as a plate with a lead glaze. Best not to eat acidic foods from it. I no longer eat from it at all, but will never get rid of it. It's not hard to check if anything is rubbing off the plate, just put the geiger counter on your finger tips.
Hello Dr. Lewin, were you serious when you said that if you did not take the copper out of the chemical solution that the students would be dead soon? And also, where is the energy coming from with the blinking lights?
+Lectures by Walter Lewin. They will make you ♥ Physics. It was around 36 minutes when you said that. And I am referring to the bouncy ball with blinking lights at 47 minutes.
+Dr. Science Sc.D "otherwise we ail all be dead by the end of the lecture" This was a joke - I made reference to the production of "fumes". What do you think is the energy source is of the bouncing ball?
41:30 you lied, but undestandably because you totally forgot that all our food production on Earth is based on solar power. Photosynthesis is the base of almost all food on Earth.Only deep down in oceans near submerged volcanoes food is produced without sunlight.
You said that that solar energy plays very little role in world's economy, but food plays a big role(1) in world's economy and all our food is based on photosynthesis eg. solar energy. So that was a lie or just a fib based on the fact that you just forgot that all food is based on solar energy. Don't get me wrong. I love this series. You're definitely one of the best physics teacher there is but even you are not fallible. (1) You only need to think about deforestration of rainforests to get more grazing land for cattle or the way oceans are depleted from fish by overfishing. One big bad example how food production destroys ecology is king crab invasion in northern Norway. It could be possible to destroy king crab from North Sea but Norway's government opposes that just because it's lucrative business.
But food consumption is energy consumption. You yourself just in this lecture calculated what is the wattage of one human being. If we didn't produce heat ourself we would need more energy to heat our apartments on winter time. I live in Finland and i was against the ban of incandescent lamps because they are more ecologyly produced than energy saving lamps including led lamps and their heat is not wasted here in Finland where when one needs light it's so cold that the heat from the lamps reduces the heating needed anyway. And during summer it's so light that one does not need lighting.
To start with you are the best. I am 16 minutes into the lecture and have a dumb question. If friction causes the bike to accelerate and the force due to friction is a constant = u_k*N , then faster pedalling should result in lower acceleration since it would decrease the resultant force in the forward direction. I know I am wrong somewhere. Can you please help me out?
faster pedaling means you are doing more work. The wheels want to rotate faster thus the frictional force on the wheels in forward direction increases. Look at it this way: suppose the friction coeff was zero (smooth ice), no matter how fast you pedal you will not move at all.
Lectures by Walter Lewin. They will make you ♥ Physics. Thank you for your reply. Can i also think of it in this way. Since the wheels rotate faster the centripetal acceleration increases which means more N and thus the frictional force (u_k*N) in the forward direction increases?
The force that I exert on the road (via the chain and the wheels) increases when I push harder on the pedals even at the start when the wheels are not rotating and when the centripetal acc is zero.
I think the blinking is caused by impulse when the ball bounces off the floor. There should be a 'generator' inside which powers the little bulb with a frequency, a generator which converts impulse of bouncing to electricity. I guess if you'd constantly bounce the ball, it would never stop blinking until that 'generator' or battery dies at some point. Correct?
we calculate esc vel of stars and planets and ignore possible atmospheres. In the case of Earth the esc vel from 100 km above the earth (where atm can be ignored) is about the same as the esc vel from the surface (ignoring atm) it's about 11 km/s.
To take the atm into account in esc vel is not practical as it differs greatly for all objects. (ask NASA). Look up tables of esc vel of planets - atm have always been ignored and that's OK because the esc vel from above the atm is nearly identical than the "imaginary" esc vel from the surface. If a satellite is in a circular orbit around the Earth, it will escape the Earth if you multiple its speed with sqrt(2).
Dear Walter, you are a great teacher and I admire your work but even you failed me during this lecture. All my student life I wondered why planets orbit the sun. I understand the physics, the maths and the equations but it took me a long time to realize that satellites are in their orbits only because they just happen to have the right tangential velocity for their orbits. Nothing is pushing them. In other words, it's all about initial conditions from the time the solar system was created. If planets were traveling faster or slower they would abandon the solar system or collapse into the Sun and they would not exist. This may seem obvious, but it's a simple beautiful fact of nature worth mentioning in a physics class.
Dear Professor. Where can I find why rotational period of the Moon fits with its orbital period around the Earth? If possible with math and phys derivation. Thank you Sir.
+Jordi GS The synchronization between spin period and orbital period is due to tidal interactions. You should search the web for articles that deal with this. Start with www.scientificamerican.com/article/is-it-just-a-coincidence/
+Jordi GS The time that it takes for the synchronization depends on masses and distances. Thus the answer to your question is "NO". PLEASE use the web to learn more about this. It's a classic in astronomy thus it should be well covered.
+Jordi GS Tidal forces fall off very fast as 1/r^3. r being the distance between the 2 objects. Thus for large distances synchronization will never occur. In fact it is believed that the synchronization for the Moon happened billions of years ago when the Moon was much closer to the Earth.
Sir in last part of your lecture on escape velocity, circular orbit you asked a question when the ball fall then after hitting the ground it glows . Sir I think there must be some material that converts the energy lost at the impact of the ball to the ground to electric energy. Similar to the photoelectric effect when energy of radiation absorbed results ejection of electrons. Sir am I right
Lectures by Walter Lewin. They will make you ♥ Physics. Sir isn't the energy lost at impact of ball to the ground is responsible for charge formation inside the material of the ball that is consumed by electromagnatic radiation at last. Sir if I am not right then what is the real answer
Lectures by Walter Lewin. They will make you ♥ Physics. Sir please tell me the answer. I went through the comments I found there is some switch... battery.... related answer. Please explain me the proper reasoning. I want the answer. Please
In the name of SCIENCE, these Lectures must be treasured & DIGITALLY PRESERVED for future generations. There will never be another Feynman, there will never be another Hawking or Sagan. And there will NEVER be another WALTER LEWIN!
:)
@@lecturesbywalterlewin.they9259❤
After a long night of physics homework, I like to sit down and relax by watching Prof. Lewin videos. Thank you so much for providing all of this free information. There is no greater pleasure to want to learn about orbital motion, or any subject in physics, and then find a video like this.
:)
8.01x Lecture 14
0:00 escape velocity
4:30 Orbital velocity
(Example: Shuttle + the moon + earth, jupiter + Sputnik 4/10/1957)
=> interesting result: v Is independent on the mass
11:55 interesting result from the equation of energy E=1/2U= -KE
13:40 Power
20:10 Heat energy
23:19 Lecture Notes, Energy and Power Consumption
28:30 various form of E
33:55 acid battery
48:00 last ex+ question
Give my thanks to Pro. Walter Lewin
thanx 2u
8.01 ocw.aprende.org/courses/physics/8-01-physics-i-classical-mechanics-fall-1999/
8.02
core.csu.edu.cn/OcwWeb/Physics/8-02Electricity-and-MagnetismSpring2002/CourseHome/index.htm
8.03
mit.ucu.ac.ug/OcwWeb/Physics/8-03Fall-2004/CourseHome/index.htm
@@lecturesbywalterlewin.they9259 Thanks Teacher, the book Physics - Ohanian now is not available for us to find, so i can not solve all the problems which is in this book. Can you help us.
@@thienthanhtranoan6723 Ofcoz I do have a copy of the Ohanian that I used in 1999 but I see no way I can help. Many problems in my assignments simply mention "problem xxx in Ohanian, page yyy". However, when you view the solutions you can guess very often what the problem was about.
@@lecturesbywalterlewin.they9259 yes sir we can study by guessing and seeing the given diagrams in the answer solutions
The definition of the viral theorem at 11:55 is very ad hoc. Even though it is absolutely correct, I feel like the deepness of this result is not well articulated, but perhaps that is to be expected for an introductory course.
Giving these lecture out for free is a great act of generosity.Knowlege is power and access to knowledge is of paramount importance in making the playing field for all players equal.We need more professor Lewins
Dear Prof. Lewin, thank you for making your lectures available to all of us. You are incredibly talented in highlighting the beauty of Physics! Thanks again!
I love the frequent jokes and fun experiments that you sprinkle throughout the lecture, it makes the lectures so much more entertaining :)
Glad you like them!
It makes him look more human. Because to me, alot of teachers (cant say abt professors, im in hs) just seem like robots burnt out and trying to get through the day while hating their job. Meanwhile Sir Walter Lewin's enthusiasm is genuinely infectious and i guess jokes naturally come as a byproduct.
What a beautiful lecture. Very conceptual and educational. Truly, Professor Walter Lewin will make love Physics.
I played with that ball many times in my chidhood..
It is having a circuit inside which blinks the light when bounced or shaked and then turns off.It's having a tiny mercury cell in it.
Mr Walter Lewin, I'm studying Engineering and Management in Germany. At first i would like to say: You're an incredible teacher! You make PHYSICS easy! Thank you very much for your lectures! They're amazing and also save my life in physics at the University. I saw in your lecture notes and assignments that you have a Guide Book. I would like to know, if possible, what book you follow in this course? Thanks for your help. Best regards, Humberto
+Humberto Carpes 8.01
Physics
Hans C. Ohanian
2nd edition
W.W. Norton & Company
ISBN 0-393-95748-9
8.02
Physics for Scientists & Engineers by Douglas C. Giancoli.
Prentice Hall
ISBN 0-13-021517-1
8.03
Electromagnetic Vibrations, Waves and Radiation
by Bekefi and Barrett.
The MIT Press
ISBN 0-262-52047-8
+Lectures by Walter Lewin. They will make you ♥ Physics. Thank you very much Mr. Lewin,
You are such a great teacher.Thank you Sir
:)
Amazing explanation and prefect elaboration of all the things, I really appreciate it..❤️
Dr. Lewin, have you done any research on the traveling wave reactor? If you have, I was wondering what your opinion of it is.
*YOU ARE TRUELY JUST AMAZING..YOU REALLY MADE ME TO FALL IN LOVE WITH PHYSICS*
Hello professor,
Regarding the ball, is the blinking because of the vibration of a spring in the ball after the bounce (vibration might cause the blinking - like a momentary switch)
I think so too
Regarding last question: When we release the ball from height h above the ground, the potential energy starts to convert into kinetic energy and by the time ball reaches ground all the potential energy is converted into kinetic energy(ignoring air drag) and now ground is stopping its motion and hence some of the kinetic energy during impact time converts into heat energy in ground and in ball as well and so inside the ball there is heat energy and jiggly motion of an atoms, and the mechanism of ball’s light is such that it converts this heat energy into an electric energy to light the bulb.
most people think like you do. Quite resanable; but your answer is incorrect.
At 02:38, isn't it equivalent to saying 0=0? Can we make those two terms equal?
31:08, I totally agree sir!
For others who are confused @ 17:27 like me...
Friction is ALWAYS opposite to the direction of motion. But in the bicycle example, friction is acting along. Also, kinetic friction is constant, as the cyclist's weight is not changing, so ideally, if it was friction from Lec-8 which was acting, then the cyclist wouldn't be able to accelerate. And the tyres would be scratching the road as it passes by causing the friction to be in opposite direction !!
So i guess the choice of word "Friction" is misleading here. It's simply a push by the ground in reaction to the push by the wheel !! Not friction from Lec-8
when an object *slips* then the friction is always opposite to direction of motion and heat is produced. Do not confuse that with an rolling object in pure roll condition; the frictional force is then not slipping and this frictional force can speed up an object (increase its rotation rate) when it is rolling down an incline - (no heat is produced)
@@lecturesbywalterlewin.they9259 Thank you sir for clarification. Love from India 😊
@@VickysTuition There are 2 types of friction, static & kinetic. If tyre overcomes static (doesn't slip on surface, object starts to move forward), kinetic friction causes bike to move forward through pure roll of the tyres.
Sir, at 2:31, how can E become 0?
Since gravitational force is a conservative force, it obeys the law of conservation of energy.
Grav PE is defined as ZERO at infinity. Thus at any finite distance r the Grav PE is NEGATIVE. If the object arrives at infinity with zero KE, then both KE and PE are zero.
Energy is conserved thus when the object leaves Earth the sum of PE and KE must also be ZERO.
36:20 Playing with H2SO4 like it's water :))
If I've done it in one of my chemistry lab, my teachers would kill me
Is IE Irodov a good numerical book to be solved with the course
Sir, it may have some spring which turns on the circuit on and off, and since the spring is not completely ideal it stops after some time.
Blessed to watch your lectures sir.
Thank you sir
Hi professor. What did you mean when you said that you wanted to make an object escape at 0 velocity in the infinity? I understood that gravitational potential energy at infinity is 0 but didn't understand about the case of kinetic energy with which any object is sent to escape the earth is also 0!! ?
+Ganesh Budhathoki Ganesh, I do not understand your question. Please make reference to what exactly I said and at what time in the videoI I said it.
+Lectures by Walter Lewin. They will make you ♥ Physics. Oh I m sorry for that. yah could you please check at 2:20 and explain that to me.
+Ganesh Budhathoki I can see why you are confused. For when the object reaches infinity with zero speed, both KE and PE are zero. Thus the amount of KE that I have to give an object to make it with zero KE to infinity is +mMG/r if I start at location r from the center of mass M. That is the minimum KE to escape to infinity - if I give it less KE it will not make it to infinity and if I give it more KE it will reach infinity with some residue KE. I hope this is clear now.
@@lecturesbywalterlewin.they9259 Sir, if the total energy is zero at infinity then where will the energy go? How the law of conservation of energy is obeyed in this case?
@@sufyanghani2425I too have this question.
If you got it pls tell.
23:05 sir what web are you talking about???
It's in the video description.
Thanks sir
You are really a legend . like Newton , Albert Einstein etc.
At 2:19 is that means the total mechanical energy throughout the motion is zero?
Please reply
@@lecturesbywalterlewin.they9259 But mechanical energy should be conserved then how could be 0 at infinity?
Please don't be offend with me:( I am a poor boy.
@@mukulbelwal yes you are right - sorry - the total energy is then zero all the way from Earth to inifnity. -MmG/r + 0.5mV^2 = 0 for any r>R, R is the radius of the Earth.
@@lecturesbywalterlewin.they9259 Please don't say sorry. I'm not deserve it by you. Just bless me. And thank for instant reply:)
In my opinion your lecture is best revision for me quick and also smooth
16:52 The Bicycle example; If Fnet(push force by legs & reaction by pedal) = 0 why isn't the pedal stationary; If Fnet = 0 , why is there a force left by pedal that pushes chain; If F friction by road = F push by tyre why is bike still moving; F kinetic means That the external force exerted must be greater than friction ; and finally u said wheels wants to rotate because your pedaling; I am totally confused; Please explain me Guru(Sir).
Sir, In the Bike example you said " I push on the pedals and the pedals push back on me, action equals to minus reaction and therefore there is no net force on the bike" but the forces are acting on the different bodies and if we consider free body diagram of the pedal, the is force which pedal exerts on you and the force which chain exerts on the pedal, so to keep it moving with constant velocity they cancel out. Is it correct?
>>>and therefore there is no net force on the bike">>>
*WRONG*
14:05 best joke ever:)
😂😂😂😂😂
Hi Dr Lewin,
I did some research on the mechanism of the ball experiment that you did at the end of this video, I wonder if the ball blinks because after it collides with the floor, the spring inside the ball gets compressed, thus the gravitational potential energy is converted into spring potential energy. After it bounces up, the spring started oscillating. It takes a period of time for the spring to stop the oscillating ( to transfer the spring potential energy into electricity which lights the electronics inside). Thus, it would blink after bouncing up.
I am not sure if my reasoning is legit. Please help me with that.
Thank you!
I really enjoy your lectures especially the demos!!
Good hypothesis but for a spring to be compressed and store the energy it requires a orientation where the loops of the spring are aligned vertically to the floor when it collides so you would expect it to sometimes blink and sometimes not blink depending on its orientation when it hit the floor but 3 springs aligned 90 degrees to each other may work regardless of orientation.
@@burningsilicon149 what about y shape spring configuration?
I thought about this too. However, if that's the case, then at the oscillation of spring would've slowed down to a stop instead of instantly switched off.
Walter Lewin is an honourable man! Yet his lectures are ambitious
Mister lewin... What about non-living things do they too radiate heat because they have temperature if yes then how does this energy come from???
Sir, I am a 10th Class Student and I watch your videos regularly.
For the last question, even I had a toy like that and that toy has an electric circuit in it with cells. So there is no extra energy produced but the electrical energy converts to light energy once circuit is triggered.
Love from India 🇮🇳🇮🇳
There might be an open circuit inside the blinky ball that is completed by an extended spring. When the ball hits the ground, some energy is transferred to the spring and it starts to oscillate, periodically completing the circuit as it extends and compresses. As the spring looses energy due to friction it no longer has enough oomph to complete the circuit and the ball stops blinking.
+Kyle Moses Kyle this is a nice idea but that's not the way this toy works.
Professor Lewin ,
You say that Power = Force * Velocity .
But force results in acceleration which results in increase in velocity .
So , what velocity do you have to plugin ?
instantaneous power is instantaneous Force time instantaneous velocity
thus at time t: Power_t=F_t*V_t
Sir I think in this there is an oscillating thing(spring) associated with the ball.The moment when ball hits the ground it may have acquire energy to oscillate .. and periodically contact with battery and hence lightning takes place as we see..!! Is above arguement is valid for this process or not?
Dear Mr Lewin, @41:49 the captions about Chernobyl is incorrect. It was not in Russia. It was in Ukraine, USSR.
thank you; what does SSR stand for?
The Chernobyl disaster was caused by a nuclear accident that occurred on Saturday 26 April 1986, at the No. 4 reactor in the Chernobyl Nuclear Power Plant, near the city of Pripyat in the north of the Ukrainian SSR.
@@lecturesbywalterlewin.they9259 soviet socialistic republic
Here is the anwer to the last question
th-cam.com/video/YGpXjzC1B0M/w-d-xo.html
The ball contains a spring or springs which starts oscillating when given suitable force to ball ,which causes led to flash for some time
33:00 at which angular velocity would one have to turn in order to create these 120 Watt?
I don't know
It depends on the type of generatore used there.
Does the ball have a battery inside with an open circuit that is completed by a spring flopping around when it feels a certain acceleration?
yes
@@lecturesbywalterlewin.they9259 that's cool
Hello Sir,
At 47:37 minutes in the lecture when the ball glows or is blinking , is it due to the mechanical energy being converted to electrical energy , like when the ball touches the ground there is some kind of spring in the ball ..that and with a battery the mechanical energy gets converted to electrical ?
And does how much time the ball blinks depend on the height from which it was thrown ..like if I throw the ball from a building or something would it glow or blink for a larger period of time as compared to while I throw in when on the ground?
your suggestion is reasonable but it is incorrect
Great lecture. Can I will your permission share it?
About the energy problem, I don't think is a tecnical problem, maybe the size of France to be full with solar pannels i too mach, but it is not if that are it will be in Sahara desert. Using all the deserts in the world, as solar power plant + using energy in a more efficient way (like California did recently), we could really resolve the energy problem.
But that's not what the problem is. The probles is that most of the politicians all around the world don't want to resolve energy or enviroment problem, and now for our missfortune they are even more ignorants than before, and even don't recognize that we have these problems.
Just to supstain my argument, in the time that this lecture was held, in my country parlament, half of them were doctors in science, and even 2 of them had their mathematic theorem recognised by Paris Institute of Technology (Even the President was a renown professor in physics, and his son worked in NASA(I'm not updated)). Todays in 140 members of the parlament just one is a doctor in science (political science!!!), and they are ruining this country.
Sir, your lecture is like Fynman lecture.
It is sad to think that solar energy is still expensive nowdays. The Sun is almost a unlimited source of energy to all mankind!
Thank you Sir for all your lectures that are keeping me motivated to get my degree on physics!!
Where can we find the explanation for the blinking Ball? I‘m too curious now, my assumption would be that the compression of the Ball plays a role in it
it's top secret
There is a battery inside the ball. And it activates when the ball is in motion
Dear Prof. Walter Lewin,
Regarding the brain teaser, may be a coil inside the moment that bounce creates acceleration and power ups the coil. Is it something like this ?
where does the energy come from?
+Lectures by Walter Lewin. They will make you ♥ Physics.
well broadly speaking, the fall, you, the food, sun, go back to 'big bang' nd beyond that probably.
Be more precise - where does the energy come that makes the ball light up when it bounces?
+Lectures by Walter Lewin. They will make you ♥ Physics.
P.E of the ball- K.E-Electric ?
+ANVAR V A
OHK !!
I just went through all the comments, Battery , switch ...
Thank you.
sorry , what does mean watch PIVot ( i always read in your assignments ) ...'????????
My physics improved a lot due to you sir.
Thanks sir god bless you ❤
Glad to hear that
Dear Dr.Lewin,
If we could put AT REST a mass 400 km from the Earth as the ISS, would it begin to orbit spontaneously? Would it fall on Earth after a few spiiral rounds? Is it necessary an initial impulse to orbit correctly? Is it possible to determine this impulse? Is there any distance from the Earth's so that the orbit began to occur in an spontaneous way?
THANK YOU!!
+Jordi GS If you released an object from the ISS which is at rest relative to the ISS then it will orbit the Earth in the same orbit as the ISS. If you throw an object from the ISS in the opposite direction of which ISS is moving and if its speed relative to the ISS is approx 8 km/s then the object has zero speed (it stands still) and it will radially fall to Earth.
Where does the energy come from of the blinking light in the ball at last, I didn't get it professor.😋
battery
@@lecturesbywalterlewin.they9259 So when the ball touches ground, the battery gets connected to the led via spring.
Is that right ??
Gets connected to ball*
@@pratikshinde2121 when the ball hits the floor (or when you bang it on the table) a switch is activated which will drive the current for a fixed amount of time.
@@lecturesbywalterlewin.they9259 Got it sir, thank you
how much of the world's energy does the US product?
accelerometer and battery inside - if te acceleromter measures anything very strong the lights flash
they do not generate energy from the impact - that might hteoretically be possible but it’s impractical and expensive you usually just have a battery that lasts very long
correct
Excellent lecture Sir. Thanks. Can you please make two videos on quantum mechanics and theory of relativity covering conclusion to best of knowledge gained so far? Regards 🙏🙏🙏🙏🙏🙏🙏
MITs courses QM 1 amnd QM 2 are on my channel. The lecturers are SUPER! For Realativity I suggest you search MIT OCW, edX, Udacity and Prof Susskind
@@lecturesbywalterlewin.they9259 bedankt!
My godness, your lectures are good
I think he forget to put r^2 instead of r during potential energy at the starting of the video 1:00 to 2:00.Correct me if i am wrong.
Potential energy has R, force has R^2
question: if a rocket is fired up at a speed less than escape velocity, in order to reach a stable orbit, is there some angle to the vertical that must be exceeded upon liftoff? for example if it goes straight up it will obviously come back down. I imagine there would be some Theta that must be exceeded in order for there to be enough tangential motion, and this would depend on the velocity and also would be very difficult to calculate.
all rockets that put a satellite in Earth Orbit start going up vertically then gradualy change that angle to optimize fuel consumption. Also watch my lecture on Kepler Oribits. I have a Physics Problem in which I address that issue.
@@lecturesbywalterlewin.they9259 ah I should've realized to wait until I saw that lecture before asking. sorry for wasting your time!! and thanks for taking the time to reply, it means a lot. stay well ❤
Its not clear how the switch turns on in order for the bulb to emit light. but the energy comes from the moving motion of the ball. the total gerenerated due to the motion of the ball depends on the gravitational constant and the mass of the ball if the consider the work done to be the dot product of force and velocity(w=F.v).
Sir,How is it possible reaching infinity at zero speed as once you give the object an uniform velocity then it maintains it.How could velocity go to zero.Please correct me if i am wrong.
Sir please can you reply...to my query
I did respond earlier. It did not get through. If an object has the escape velocity at distance R from the center of a mass M, its speed will decrease all the time as it always experiences the gravitational pull from M. It will take infinitely long to reach "infinity". But it would then get there with speed zero. Infinity is a difficult concept. It has only mathematical meaning. If you calculated the "escape" speed the object would need to reach a distance of 100 million light years, you would find the same value (at least the first 9 digits would be the same) for that speed. That's not so difficult to grasp.
Thanks a lot sir..
Sir I think that there is a potential energy mgh when we throw the ball and then at the moment it hits the ground that gravitational potential energy turns into kinetic energy and a potential energy which squeezes the ball when it hit the ground. Then this squeezing potential energy turns into electrical energy which make a light bulb (which is programmed to blink) blink. Is it right?
incorrect
Lectures by Walter Lewin. They will make you ♥ Physics. May you tell me the reason sir please?
try harder
maybe LED is situated in a group of -ve springs with some space between them and +ve terminal of led is already attached to the battery
so when ball collide with floor then system becomes unstable and LED moves back and forth and circuit will start switching between on and off.
but i don't know why duration between two flash of lights is looks like so uniform?
sir for power we have two formula. is dw/dt used for power increased or decreased of system in some amount of time. and f*v*cos(theta) for instantaneous increment or decrement of power for a system?
if that's what I state in my lecture then it is correct.
26:50 actually its 34,335 so its more embarrassing power
"it' much nicer to have a human being with you in bed than one blanket"
-professor lewin
31:00
Is there a piezoelectric material that converts kinetic eb=nergy in elctrical energy?
ask google
My answer for brain teaser...
As the ball hits the ground the gravity does the postive work on the ball....and when it comes back to u it will light up till the rate of the change of the work provides sufficient amount of power to light up that bulb.
Sir Please let me know ...
Am i thinking in right direction?
8:45 I found Mark Zuckerberg sitting in the middle, wearing a stylish spectacular. XD
31:10 ;)
Sir, can we say that if we intake more calories than required, body increases its surface area (which is proportional to size) to increase the heat rejection to maintain the temperature?
>>>can we say that if we intake more calories than required>>>
depends on what you mean buy "required".
prof can u give me data how u calculated ur daily energy consumption and how u calculated tht this is equivalent to having 100 workers working continuous for 12 hrs?
Sir i don't have the book u use i can't also buy bcoz it's very very very expensive in india
Great explanation
On an exaggerated scale, would the ball not bounce as high as one without or is the loss of energy converted to negligible.
I do not understand your question. "as one without" without WHAT?
also let me know how many minutes into the video
Lectures by Walter Lewin. They will make you ♥ Physics. I believe his question is that if the ball uses gravitational potential energy to power the led’s than the mechanical energy of the ball decreases because some of it is converted into light energy which leaves the ball so it will not reach the initial height it started at because mgh is now smaller than it was initially and is the light energy radiated a significant fraction of the gravitational potential energy to decrease its height by a measurable amount.
Dear Professor..
I want to ask you said that the force of friction(F,fr)is acted on the direction of your force forward?Isnt friction (F,fr) acing opposite to the force(F,WL) ..
Thank you
question unclear. Refer to how many minutes into which lecture and rephrase the question.
Ohh now I know professor.. After im thinking for a minute...The rotation of the wheel is clockwide which is to the left ,so must be the friction acted is to the opposite of the rotatio of the wheel...Ohh Poor me...
how come 'the ameriacns ' find the orbital velocity @10:09
question unclear.
we know T=2piR/v(orbital)
You said that since we know the time period we can easily calculate 'R' and 'v'.How come we can calculate both v and r from a single equation.
Also if we use second relationship in terms of mass we dont have mass of earth and radius.
Then how come at the time of sputnik did they calculate 'R' and 'v'
looks like i got it wrong may we you meant that we dont know the mass of sputnik.
Kindly correct me if I am wrong.before launching of sputnik we knew the mass of earth and calculated it by using f=GMm/r^2 .
Indeed the US could not determine form the orbital parameters what the mass was of sputnik. Orbital radius and orbital speed were a piece of cake.
Concerning the brain teaser, I don't understand how a battery can be turned on (a switch) just by hitting the ground (is there a special mechanism) and why it keeps blinking just for a while? Are we talking about a capacitor that is charging while you are holding the ball and discharge, immediately after touching the ground, into a light-bulb allowing it to blink momentarily until the voltage across the capacitor come to a value (a threshold) and than stop. THANK YOU SO MUCH FOR YOUR HELP! Sir WL
place a switch in the circuit. You can turn the switch ON and OFF. This has nothing to do with grounding.
30:59 - 31:18 is the best part...
Thank you, Professor, that was cool!
Here is my try on the brain teaser.
When the ball hits the surface, there is heat generated. Maybe there is a detector which detects this sudden change in heat and responds to it by blinking. Afterwards, the heat radiates out and the ball comes back to nearly it's initial temperature?
incorrect
Dear Sir, As mention in the lecture, how can we find the mass of a orbiting satellite when we know the time period alone.
mass cannot be determined if we know the orbit
my uncle worked at PPPL. i heard all about fusion: by 2000, no more petrol, a thermos of water etc etc etc. yada yada yada. i truly believed it, but i'm still waiting... i did get inside the tokamak, tho when it was down, walked about, which was pretty cool.
that too is long gone. no idea what they are doing at pppl these days. i guess still hammering away at it.
since the conservation of energy, energy is conserved, noe destroyed neither created. Is there a limit amount of energy in the entire universe? An approximation?
use google
Wow
sir, I have a doubt. Energy required to lift an object is mgh but how much energy is required to hold that object for x seconds.
to hold it for 20 years requires ZERO energy. Place the object on a shelf.
Do you think the shelf has to do any work?
Lectures by Walter Lewin. They will make you ♥ Physics. But then, why does our hand start to hurt if we hold it for a certain amount of time?
thats to do with biology, i think lactic acid buildup or something, but in terms of physics, no energy is transferred over the duration you are holding the object up for. Pain or effort =/= transferring energy
five 505 that’s because only your muscles are doing the internal work,they contract and expand repeatedly,that’s why they hurt,the work is being done internally not externally as the object isn’t experiencing any work.
Sir sometimes books says gravtational potential energy is mgh and sometimes -GmM/R. Sir what is difference between the two
near Earth where grav acc is constant mgh is fine. At large distances we have to do better and we define that PE is zero at infinity. Then PE at distance r is -MmG/r I cover this in my lectures
@@lecturesbywalterlewin.they9259 sir is you beleive in GOD
Does the blinking of the ball depend on height?
no - but there is a minimum height approx 30 cm
Is there an optimal angle for take off? ..and if so how is this calculated? Pretty much as soon as any rocket "clears the tower" it goes into a roll procedure and angled ascent as quickly as possible.
how many minutes into the lecture?
The first 17 minutes or so--you talk about the the velocity, but don't mention the angle of ascent. As soon as any rocket clears the tower it "rolls" and ascends with a marked angle to the ground. I saw the shuttle lift off, and I expected it to take off straight, but it takes off at an angle off about 25-30deg away from perpendicular after about 10 seconds after lift-off.
I imagine there must be a pretty strong reason why they do this (gaining altitude and angular velocity) but surely this would mean that the vehicle must pass through more of the dense lower atmosphere, and this would affect the required escape velocity.
I have sent your question to my friend the Astronaut Professor Jeff Hoffman. I will send you his reply.
I have not heard yet from Jeff but I have thought about this a bit. When a satellite gets into Earth orbit, it's velocity (about 8 km/s) must be tangential to a near circular orbit. ISS and the Shuttle used to be about 200 miles above the Earth surface. Suppose you go straight out of the atmosphere along the vertical direction then you arrive at 200 miles with a radial velocity but that is NOT what you need. You must end up with a velocity which is 90 degrees away from radial. Thus the fact that the shuttle changes direction soon after launch is probably a matter of fuel economy. Leveling off early on in the launch is more fuel-efficient than first going vertically up to 200 miles with a velocity radially outwards and then changing the direction of motion by 90 degrees. By doing that you would also not stay at 200 miles but you would end up at a much larger distance form Earth. Thus you MUST level off (change direction) sooner to end up in near circular orbit about 200 miles up.
Here is the answer from Professor Hoffman:
It is correct that getting above the dense lower atmosphere is important, but there is always a compromise between getting high quickly and starting to accelerate horizontally to eventual orbital velocity of ~18,000 mph. Going straight up is extremely inefficient for a rocket. This is referred to as “gravity loss”. It has to be balanced against atmospheric drag loss. The most efficient way to transition from going straight up out of the launch tower and getting into a horizontal trajectory is called a “gravity turn”. You use the rocket’s steering to start tipping the rocket just a small bit, then gravity pulls it over the rest of the way, so that the rocket thrust can continually be applied parallel to the direction of motion. Any rocket thrust applied sideways to turn the rocket, since it is perpendicular to the direction of motion, will not increase the energy of the rocket. That is why gravity turns are the most efficient.
Another consideration is that while carrying out the gravity turn, the rocket gets into the plane of its desired orbit. The sooner this is done (i.e. at the lowest velocity possible) the less cost there is to establish a new orbital plane.
sir I have a question.. as we know that escape velocity=√2gr then from here can we say that from centre of the earth the escape velocity is 0... i mean this feels quite non intuitive..
No that's wrong! THINKKKKKKKKKKKKKKKKKKKK
Lectures by Walter Lewin. They will make you ♥ Physics.
Lectures by Walter Lewin. They will make you ♥ Physics.
give us a clue at least prof.... btw thanks for uploading these videos sir, this is just really helpful!!!
oh wait... there the term r, literally means radius and not the distance, so we cannot have an object with radius 0m, that makes the whole question wrong..... Am I right sir ?
Are those fiesta red dishes harmful???
not if you use them in a normal way.
I have the same plate.They are beautiful (and there's something unique about the orange color-you can match it until you can't tell the difference, but the non-uranium color won't 'feel' the same.) I ate from it for 20+ years. I emailed the safety question to Theodore Gray who makes books on the elements of the periodic table. He said there is a risk from the plate, but it is not the radiation, it's that uranium is a heavy metal. So its about the same risk as a plate with a lead glaze. Best not to eat acidic foods from it. I no longer eat from it at all, but will never get rid of it.
It's not hard to check if anything is rubbing off the plate, just put the geiger counter on your finger tips.
Hello Dr. Lewin, were you serious when you said that if you did not take the copper out of the chemical solution that the students would be dead soon? And also, where is the energy coming from with the blinking lights?
+Dr. Science Sc.D how many minutes into the lecture do I say this? What blinking lights?
+Lectures by Walter Lewin. They will make you ♥ Physics. It was around 36 minutes when you said that. And I am referring to the bouncy ball with blinking lights at 47 minutes.
+Dr. Science Sc.D "otherwise we ail all be dead by the end of the lecture" This was a joke - I made reference to the production of "fumes". What do you think is the energy source is of the bouncing ball?
I think the energy source is from gravitational potential energy but I'm unsure of why it is in still blinking, is it due to kinetic energy?
+Dr. Science Sc.D That is not a bad guess but it is incorrect
41:30 you lied, but undestandably because you totally forgot that all our food production on Earth is based on solar power. Photosynthesis is the base of almost all food on Earth.Only deep down in oceans near submerged volcanoes food is produced without sunlight.
what I said was not a lie, it's correct. I suggest you listen more closely to what I said.
You said that that solar energy plays very little role in world's economy, but food plays a big role(1) in world's economy and all our food is based on photosynthesis eg. solar energy. So that was a lie or just a fib based on the fact that you just forgot that all food is based on solar energy.
Don't get me wrong. I love this series. You're definitely one of the best physics teacher there is but even you are not fallible.
(1) You only need to think about deforestration of rainforests to get more grazing land for cattle or the way oceans are depleted from fish by overfishing. One big bad example how food production destroys ecology is king crab invasion in northern Norway. It could be possible to destroy king crab from North Sea but Norway's government opposes that just because it's lucrative business.
what I said was correct. I discussed the world energy consumption - please listen more carefully.
But food consumption is energy consumption. You yourself just in this lecture calculated what is the wattage of one human being. If we didn't produce heat ourself we would need more energy to heat our apartments on winter time.
I live in Finland and i was against the ban of incandescent lamps because they are more ecologyly produced than energy saving lamps including led lamps and their heat is not wasted here in Finland where when one needs light it's so cold that the heat from the lamps reduces the heating needed anyway. And during summer it's so light that one does not need lighting.
you are confused - listen more closely - en.wikipedia.org/wiki/World_energy_consumption
Thanks a ton sir.
To start with you are the best. I am 16 minutes into the lecture and have a dumb question. If friction causes the bike to accelerate and the force due to friction is a constant = u_k*N , then faster pedalling should result in lower acceleration since it would decrease the resultant force in the forward direction. I know I am wrong somewhere. Can you please help me out?
faster pedaling means you are doing more work. The wheels want to rotate faster thus the frictional force on the wheels in forward direction increases. Look at it this way: suppose the friction coeff was zero (smooth ice), no matter how fast you pedal you will not move at all.
Lectures by Walter Lewin. They will make you ♥ Physics.
Thank you for your reply.
Can i also think of it in this way. Since the wheels rotate faster the centripetal acceleration increases which means more N and thus the frictional force (u_k*N) in the forward direction increases?
The force that I exert on the road (via the chain and the wheels) increases when I push harder on the pedals even at the start when the wheels are not rotating and when the centripetal acc is zero.
Lectures by Walter Lewin. They will make you ♥ Physics.
Got it. Thank you Professor.
I think the blinking is caused by impulse when the ball bounces off the floor. There should be a 'generator' inside which powers the little bulb with a frequency, a generator which converts impulse of bouncing to electricity. I guess if you'd constantly bounce the ball, it would never stop blinking until that 'generator' or battery dies at some point. Correct?
there is a battery inside - at each bounce a switch triggers the connection for a few sec with the light bulb.
@@lecturesbywalterlewin.they9259 aha! Thanks for the answers
Cliff hanger resolved:rotational KE
How will having atmosphere affect the calculations (0:23)?
how will it affect the calculations?
DO you mean the drag force??
we calculate esc vel of stars and planets and ignore possible atmospheres. In the case of Earth the esc vel from 100 km above the earth (where atm can be ignored) is about the same as the esc vel from the surface (ignoring atm) it's about 11 km/s.
yes air drag
so why are you ignoring it even though you have already taught it in Lecture-12?
To take the atm into account in esc vel is not practical as it differs greatly for all objects. (ask NASA). Look up tables of esc vel of planets - atm have always been ignored and that's OK because the esc vel from above the atm is nearly identical than the "imaginary" esc vel from the surface. If a satellite is in a circular orbit around the Earth, it will escape the Earth if you multiple its speed with sqrt(2).
Dear Walter, you are a great teacher and I admire your work but even you failed me during this lecture. All my student life I wondered why planets orbit the sun. I understand the physics, the maths and the equations but it took me a long time to realize that satellites are in their orbits only because they just happen to have the right tangential velocity for their orbits. Nothing is pushing them. In other words, it's all about initial conditions from the time the solar system was created. If planets were traveling faster or slower they would abandon the solar system or collapse into the Sun and they would not exist. This may seem obvious, but it's a simple beautiful fact of nature worth mentioning in a physics class.
Dear Professor. Where can I find why rotational period of the Moon fits with its orbital period around the Earth? If possible with math and phys derivation.
Thank you Sir.
+Jordi GS The synchronization between spin period and orbital period is due to tidal interactions. You should search the web for articles that deal with this. Start with www.scientificamerican.com/article/is-it-just-a-coincidence/
+Lectures by Walter Lewin. They will make you ♥ Physics. Does it occurs with any moon around any planet?
+Jordi GS The time that it takes for the synchronization depends on masses and distances. Thus the answer to your question is "NO". PLEASE use the web to learn more about this. It's a classic in astronomy thus it should be well covered.
+Lectures by Walter Lewin. They will make you ♥ Physics. THANK YOU!!!!
+Jordi GS Tidal forces fall off very fast as 1/r^3. r being the distance between the 2 objects. Thus for large distances synchronization will never occur. In fact it is believed that the synchronization for the Moon happened billions of years ago when the Moon was much closer to the Earth.
Sir in last part of your lecture on escape velocity, circular orbit you asked a question when the ball fall then after hitting the ground it glows . Sir I think there must be some material that converts the energy lost at the impact of the ball to the ground to electric energy. Similar to the photoelectric effect when energy of radiation absorbed results ejection of electrons.
Sir am I right
NO
Lectures by Walter Lewin. They will make you ♥ Physics. Sir isn't the energy lost at impact of ball to the ground is responsible for charge formation inside the material of the ball that is consumed by electromagnatic radiation at last.
Sir if I am not right then what is the real answer
You will hate the real answer. I therefore prefer not to tell you.
Lectures by Walter Lewin. They will make you ♥ Physics. Sir please tell me. I never hate the facts and truth.
Lectures by Walter Lewin. They will make you ♥ Physics. Sir please tell me the answer. I went through the comments I found there is some switch... battery.... related answer. Please explain me the proper reasoning. I want the answer. Please