Water play!

Water pushes up on an object. Whether it floats depends on its weight and how much water it pushes aside—not simply on whether it looks big or small. The wood, cork, and hollow duck here float; the rock, metal ball, and solid clay sink.

A ball of clay sinks. A hollow boat made from the same amount of clay can float. Try the clay in the first activity, then compare the two boats.

Adding cargo makes the boat sit lower. The wider boat can push more water aside before its rim reaches the water. Undo rewinds one ball; Start again empties the boat. Waves add a gentle rocking motion, without changing the load experiment.

This is a simplified water model with fixed example materials and dry, hollow boats. Try real objects together and compare your discoveries.