This is not homework, but the question is really bugging me. [Link to Yahoo Answers Question](adsbygoogle = window.adsbygoogle || []).push({});

Here is the problem:

On a scale, you place a glass of water and a ball on each side of the scale. The scale is balanced at this point. If you take the ball on side B of the scale, and place it into the glass of water on side B and the ball floats, will the scale become unbalanced?

Although the posters on Yahoo Answers think that the scale will remain balanced, I think not. The scale only detects the forces acted on each side. Because the ball floats, there is a buoyant force from the displaced water that is preventing the ball to sink to the bottom, thus the ball's force of gravity is not acting on the scale.

For side A:

[tex]\Sigma F_A = F_{G}_{water} + F_{G}_{ball}[/tex]

For side B:

[tex]\Sigma F_B = F_{G}_{water} + (F_{G}_{ball} - F_{buoy}) = F_{G}_{water}[/tex]

Can someone please confirm/correct.

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# Bouyant Force on a Scale

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