In a closed glass tank which is filled with water to the brim, there are two spheres, one of cork and one of lead. The cork sphere is fixed to the bottom by a thread to prevent it from rising further; the lead sphere hangs from a thread fixed to the top of the tank. The lengths of the threads are such that the lead sphere is hanging just above the cork sphere. Explain what happens from the point of view relative to the tank and from the point of view relative to the Earth, if the tank is now suddenly moved to the right.

           __________________
          |        |         |
          |========|=========|
          |========|=========|
          |========|=========|
          |========O=========|  <----- lead sphere
          |==================|
          |========O=========|  <----- cork sphere
          |========|=========|
          |========|=========|
          |========|=========|
          |________|_________|

I agree with Charlie's analysis and solution.

I think the kool-aid example does not apply, since the much smaller size of the particles would lead to drasctic re-sizing of inertia vs. viscous forces that would make the kool-aid and sugar look like they were still, but the forces are there none-the less.

Also, it is not the compressablility of the air that makes the balllons move into the turn in your car, it's the change in the vector of the net accleration field - again per Charlie.

Boyancy forces oppose the net gravity field, but since acceleration can equate to gravity, that's why it happens.

Posted by Kenny M on 2006-01-07 18:57:50