Question

Explain the following:

A small boy balances a grown up man on see-saw.

Answer 1

The see-saw is balanced because the turning moments (torques) about its fulcrum are equal and opposite. The grown-up man has greater weight, so he sits closer to the fulcrum; the lighter boy sits farther away. Since moment = force × perpendicular distance, their moments balance: boy’s weight × his distance = man’s weight × his distance. Thus, the net moment is zero and the see-saw stays horizontal.