Does it float? Boat test
Some things float and some things sink. A piece of wood floats. A coin sinks. A boat can be made of heavy material, but it still floats. This is because its shape is wide and hollow, with air inside. A flat square of foil squeezed into a ball sinks. The same foil folded into a boat with high sides floats. If we put too much cargo in a boat, it sits lower and lower in the water. At last the water comes in and the boat sinks. To test a boat, we make a prediction first. Then we add cargo one piece at a time, and we count.
Foil boat test (with a grown-up). You need a bowl of water, a hand-sized square of foil and about 20 big buttons or flat stones for cargo. First guess: how many pieces will your boat hold? Fold the foil into a boat with high sides. Set it on the water. Add one piece at a time and count. Stop when it sinks. Write the number. Now make the boat wider and test again. Dry your hands and wipe the table. Never test boats at the river without a grown-up.