Question

Which dam should be stronger, one that must hold back 100,000 $m^3$ of 10 m deep water or one that must hold back 1000 $m^3$ of 20 m deep water? Give reasons.

Answer 1

Liquid pressure is directly proportional to the depth of the liquid from the free surface. At the bottom of the dam, there is high water pressure. To protect the dam from the high water pressure, the bottom is made wide and stronger than the upper part. A dam is thicker at the bottom than at the top because the forces exerted are strongest close to the ground. Water pressure increases proportionally with depth, so the lower portion of the dam has greater water pressure exerted upon it. The increasing thickness of the lower dam also helps it to support its own weight. Thus, the dam which holds back 1000 $m^3$ of 20 m deep water should be stronger.