Kappa, just like the spring constant k have to be experimentally determined. Apply a known torque and measure the amount of deflection.

Thank you! Cheers!

It wasn't easy, but the experiment was brilliant and actually worked quite well.

That is correct.

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!

That is correct.

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?

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.

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.

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?

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

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

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

it is the universal constant of gravity, it is experimentally derived.

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.