Look at a boat on a lake. It is big, and it does not sink. What holds it up? Here are the clues. Let us find them.
A solid lump of clay sinks in water. So does a lump of iron.
But if you mold that clay so it looks like a boat, it will float.
Even heavy material can make a boat that floats. The boat has to be hollow and full of air, not a solid lump.
Here is the first clue. Water pushes up on anything that is in it.
Here is the next clue. What keeps a boat afloat? The push from the water against a boat's bottom.
Why does a big ship stay up? Its inside holds lots of air.
An empty ship rides high in the water. Load it with cargo, and the same ship sits lower.
A submarine dives when it lets water fill its ballast tanks.
Life jackets help a person float. Children should wear one, and so should everyone else in a boat.
Water play and swimming need a grown-up watching. Always ask first.
Words to know
- hollow: empty inside
- cargo: a ship's load
- ballast: water tanks
- afloat: floating
