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Consider the following situation:

Two balls are inside a jar with diameter $D$. The balls are uniform in mass and both have the same diameter $d$.

enter image description here

Express the forces that acts at the colored dots in the figure.

Could any body give me a hint? It seems to me that I can't express one force without using the other.

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closed as off-topic by John Rennie, Danu, Chris White, Kyle Kanos, Bernhard Aug 29 '14 at 13:23

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Homework-like questions should ask about a specific physics concept and show some effort to work through the problem. We want our questions to be useful to the broader community, and to future users. See our meta site for more guidance on how to edit your question to make it better" – John Rennie, Danu, Chris White, Kyle Kanos, Bernhard
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You know there is a force $mg$ acting downwards at the centre of each ball. You known the balls aren't rotating so the moments of the forces add up to zero, and the balls aren't accelerating so you know the forces on each ball must add up to $mg$ upwards. So you can down a series of simultaneous equations relating the forces. – John Rennie Aug 29 '14 at 10:43
I solved the question. Thanks to both of you. – Udi Behar Aug 29 '14 at 11:27

Consider this for the upper ball:

enter image description here

The angle of the inclined plane is simply derived from geometrical considerations. Looks pretty easy to solve, right? Once you know the normal force of the inclined slope, reflect and apply it to the bottom ball to complete the problem.

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Very good approach. The right diagram makes all the difference. – Floris Aug 29 '14 at 12:13

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