perplexus.info :: Science : Two spheres in a tank

Two spheres in a tank (Posted on 2006-01-05)

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
          |========|=========|
          |========|=========|
          |========|=========|
          |________|_________|

Submitted by pcbouhid

Rating: 3.5000 (2 votes)

Solution: (Hide)

If the tank is suddenly moved to the right, inertia will cause the lead sphere to move to the left relative to the tank. The lead sphere tends to persist in its state of rest. It is true that the water tends to do the same thing, but the sphere, wich is so much heavier than the displaced water, dominates the situation. With the cork sphere, which is lighter than the water displaced, the reverse is true; hence, this sphere move to the right, even relative to the tank. If the tank is moved to and fro, the two spheres will also be observed to move to and fro relative to the tank, the cork sphere in the same direction as the tank every time, the lead sphere in the opposite direction.

Relative to the Earth, the tank and the two spheres always move to the same side, but for the lead sphere the oscillations are smaller, and for the cork sphere larger, than the oscillations of the tank.

Comments: ( You must be logged in to post comments.)

Subject	Author	Date
ANSWER:	GK2004	2006-08-31 21:59:45
RE: about sugar????????	Tonja	2006-02-04 03:05:26
re: about sugar	Hugo	2006-01-10 14:16:28
about sugar	Jer	2006-01-10 12:46:03
re(2): Agree with Charlie - more comments	Hugo	2006-01-09 08:42:13
re: Agree with Charlie - more comments	Kenny M	2006-01-08 19:13:24
Agree with Charlie	Kenny M	2006-01-07 18:57:50
Sugar in koolaid	Jim	2006-01-06 23:29:36
according to Einstein	Charlie	2006-01-05 13:25:03
re: First Thoughts (Second thoughts)	Sing4TheDay	2006-01-05 11:31:51
First Thoughts	Rollercoaster	2006-01-05 10:16:46

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