Torque:

$\overline{){\mathbf{\tau}}{\mathbf{=}}{\mathbf{rF}}}$

Sum of torque in rotational equilibrium:

$\overline{){\mathbf{\Sigma}}{\mathbf{\tau}}{\mathbf{=}}{\mathbf{0}}}$

Counterclockwise is positive.

Learning Goal: To make the connection between intuitive understanding of a seesaw and the standard formalism for torque. This problem deals with the concept of torque, the "twist" that an off-center force applies to a body that tends to make it rotate. (Figure 1)

Use your intuition to try to answer the following question. If your intuition fails, work the rest of the problem and return here when you feel that you are more comfortable with torques.

Marcel is helping his two children, Jacques and Gilles, to balance on a seesaw so that they will be able to make it tilt back and forth without the heavier child, Jacques, simply sinking to the ground. Given that Jacques, whose weight is W, is sitting at distance L to the left of the pivot, at what distance L_{1} should Marcel place Gilles, whose weight is w, to the right of the pivot to balance the seesaw?

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