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.

 

[PJC01]

The Eötvös experiment is a classical physics experiment designed to test the universality of free fall, which states that all objects in a vacuum fall with the same acceleration regardless of their mass. The experiment was first performed by Hungarian physicist Loránd Eötvös in 1889 and has since been replicated numerous times with increasingly precise results.

To address your question, the concept behind the Eötvös experiment is to measure the difference in the gravitational accelerations of two objects with different masses. The centrifugal forces on the two objects, as you mentioned, cancel out due to the equal and opposite forces acting on them. This allows us to focus solely on the difference in gravitational accelerations.

In order to obtain high accuracy in the experiment, careful adjustments and measurements are indeed necessary. The positions of the objects must be precisely adjusted so that the gravitational forces acting on them are equal, allowing for a balanced system. This is typically achieved by using a torsion balance, which is a sensitive instrument that measures the small differences in gravitational accelerations.

Additionally, the experiment is typically conducted in a vacuum to eliminate any potential external forces that may affect the results. This allows for a more controlled and accurate measurement of the gravitational forces.

Over the years, advancements in technology and improvements in experimental techniques have allowed for increasingly precise results in the Eötvös experiment. This includes using more sensitive instruments, such as the Cavendish balance, and conducting experiments in microgravity environments.

Overall, the Eötvös experiment has been a crucial tool in testing the universality of free fall and has provided valuable insights into the fundamental laws of physics. I hope this helps to clarify the concept behind the experiment and how physicists are able to obtain high accuracy in their results.