Question about Eötvös experiment

[davidchen9568]

I do not understand the concept. Let the centrifugal forces on the two objects are F1 and F2. The rod will not rotate because net torque is 0. That is, F1r1=F2r2. That Does that mean we have to carefully adjust the positions of objects (before experiment) so that m1gr1=m2gr2? Then we conclude F1/m1=F2/m2 (to very high accuracy)?

If it's like what I said, how can phycisits obtain very high accuracy? Even if m1gr1 does not exactly equal to m2gr2, I believe the system can balance somewhere, thus create a error far larger than 1/20,000,000.

So how was that done?

Article on Wikipedia: http://en.wikipedia.org/wiki/Eötvös_experiment

 

[256bits]

The system does balance somewhere and you record it.
Then you switch places of the two masses on the rod, or rather it is easier to turn the whole apparatus 180 degrees around.
A null result, meaning that the rod does not twist in the opposite sense, confirms the equivalence principle.

 

[TurtleMeister]

G₁ and G₂ depends of the passive gravitational mass of m₁ and m₂ respectively. F₁ and F₂ depends on the inertial mass of m₁ and m₂ respectively.

If the ratio of F1 to F2 would differ from the ratio of G1 to G2, the rod would rotate. The mirror is used to monitor the rotation.

For example: if the passive gravitational mass of m₁ were made to be less than the inertial mass of m₁, then gr1 would become greater, and gr2 would become less. (The balance point would change.) So applying the force F₁ and F₂ would cause the rod to rotate.

Edit:
Greater accuracies and sensitivities have been achieved since the EotVos experiments. You may want to check out http://www.npl.washington.edu/eotwash/.

 

[davidchen9568]

Thanks a lot for the link. I will read them.