Physics 16.6 Torsion (10 of 14) Determining G with the Cavendish Torsion Pendulum
ฝัง
- เผยแพร่เมื่อ 28 ส.ค. 2024
- Visit ilectureonline.com for more math and science lectures!
In this video I will find the universal gravitational constant G=?, using Cavendish's experiment of torsional balance.
Next video in this series can be found at:
• Physics 16.6 Torsion ...
![[UNCUT] The Loyal Pin ปิ่นภักดิ์ EP.4 (4/4)](http://i.ytimg.com/vi/d3l5rxl5CVo/mqdefault.jpg)
I just came to see if any flat earthers were spouting off in the comments section.
My work is done here.
You guys are very helpful. Without this video my presentation would be a fail. Thanks alot.
Wow , you already made video about , so I don't need to ask for it
Very impressive!. Very nicely done
Thank you! Cheers!
Great presentation. Very concise and informative. I see that frequency, torque and period are all functions of kappa. Can you tell me where the kappa term comes from? What section of a physics book would that be under?
Kappa, just like the spring constant k have to be experimentally determined. Apply a known torque and measure the amount of deflection.
Thank you so much. Very clearly explained.
Was this the same way Coulomb's constant was determined?
Coulomb forces are MUCH stronger, so that was easier to perform. The hard part there was to discover the value of a single charge, which was performed with the incredible Millikan experiment.
@@MichelvanBiezen Please could you do a video on that too?
If Newton made G based formula much earlier then this experiment then how did Newton put G on his equations without knowing the value of G
Every equation in physics needs a constant to turn it from a relationship (or proportionality) into an equation. Newton realized that the force of gravity was inversely proportional to the distance, and was proportional to the product of the masses. To make it into an equation, you need a constant (even if you don't know what the constant is). Then you start devising experiments to determine the value of the constant, which is then refined and made more accurate over the years. So you don't need to know the value to make the equation.
@@MichelvanBiezen thanks !! So what number of Gravitational constant he ( Newton ) did estimated for his equation ? During that day ?
At the time Newton had no way to calculate the value. However before Cavendish's experiment gave us an accurate value, initial values were found by estimating the average density of the Earth.
@@MichelvanBiezen thank you sir
Wonderful.
But Professor, how accurate the value G can be when this experiment is done in an environment full of other objects, and every two object absorb each other? And also inaccuracies in measuring tools and measurement readouts?
Thank you.
It wasn't easy, but the experiment was brilliant and actually worked quite well.
Maybe instead of M should be M + m ?
because if m = 2.5724 * kg
then it is G = 6.6740829 * ( 10 ^ -11 ) * N * ( m ^ 2 ) / ( kg ^ 2 )
while if m = 2.329 * kg
then it is G = 6.684215 * ( 10 ^ -11 ) * N * ( m ^ 2 ) / ( kg ^ 2 )
Otherwise it is very well explained , the laudable
The video is correct as is. Thank you for checking.
How much is the small mass in the experiment ?
Cavendish experiment has been made ago more than 200 years ago, later a corrections have been made
expression for gravity constant is 4 * ( pi ^ 2 ) * ( A ^ 3 ) / ( T ^ 2 ) = G * ( M + m )
You can view my video for the approximate calculation of the system masses " My empirical correction of third Kepler law for entertainment ; Silvio Sponza " and read my video explanation
Hi sir, at 2:23 why do we need to multiply torque by 2? Haven't u done it in the first line?
The first doubling is because we have 2 sets of masses. But that torque is the torque required to move the small mass through an angle from the equilibrium point to the maximum angle. Doubling a second time will give us the torque required to move from the + maximum angle to the - maximum angle, (twice the distance).
@@MichelvanBiezen Ahh..Thanks a lot!
He couldn't isolated gravity from that room.. so wires balls and all objects are under g force.. no point what about centrifugal force.. plus altitud.. and magnetic force regarding the field... no sense just formulas. .. that do not get you anywhere...
The experiment ended up to be hugely succesful and accurate.
@@MichelvanBiezen compare to what...?do you know that no one knows why gravity as that value?
Most of the constants in physics are experimentally determined (like G), but we don't know why they are that value.
@@MichelvanBiezen thx for your answer and your time I'm really appreciated...have a great day
'He couldn't isolated gravity from that room.. '
Exactly. That is why a torsion balance was used.
Centrifugal force would not have been an issue, neither would altitude. A magnetic field able to move a 158kg ball would be detectable and measurable, most assuredly.
The fact that our understanding of Newtonian gravity allows us to send space craft into orbit around nearby planets with a high degree of precision leads me to believe that our understanding of Newtonian gravity, while not complete, is profound.
I am having trouble understanding why you doubled the torque to calculate delta torque. Your derivation differs as a result by a factor of 2 from what is shown here: en.wikipedia.org/wiki/Cavendish_experiment
Also what is delta theta in your diagram? Is it 2 theta because of both sides? That might explain the difference in interpretation.
Also where did you find the 7.45mm and 852s? I find values for T as 20 min or 1200s and no values for the arc length.
Thanks!
Torque = F x distance. Since we have two small masses and 2 large masses we have to account for the torque caused by each pair and thus total torque = 2 x F x d
I don’t completely understand d*(delta)(theta) and how you measure it??
d is the distance from the center of the rod to the center of one of the spheres on the rod.
delta indicates "change in the following quantity"
delta theta indicates change in the equilibrium angle position after the fixed masses are introduced, from the original resting position.
Does d span only half of the rod?
That is correct.
i dont understand something. The torsion force is tangential but the gravitational force is not, then, how can I equate these equations?
The gravitational force is between the spheres, not the spheres and the Earth, therefore they are in the same plane as the torsion force.
@@MichelvanBiezen Thank you for answering. I know they are in the same plane, but torsion force is tangential to the circle the small spheres make when they rotate, but the gravitational force is not tangential, gravitational force point in the line that join the big and the small mass. Then how can I equate both forces?
Thank you, this this great video!! I got one answer. why ecuation is T=2π^2√(I/K), and not T=2π^2√(m/K)? how I and not m? why you not considerate cilinder mass I=1/12ML^2?
Question 1: I is the moment of inertia and the equation is correct. Question 2: we ignore the mass of the bar which is insignificant to the masses of the 2 spheres.
Michel van Biezen so what k(kapa) stands for? in case of that moment of inertia
@@justinjames577 kappa is the torsional constant of the wire that supports the rod and masses. It has the units Newton-meters per radian. It is the rotational equivalent of the spring constant for a linear spring.
That period T was calculated without the big Ms right?
That is correct.
from where the value of G has come
it is the universal constant of gravity, it is experimentally derived.
Nothing compared to the other non helping Videos here on youtube.