How Do Boats Float

A boat made of steel is heavier than water, so how does it float? The secret is the boat's shape. A boat is hollow inside, which means it takes up a lot of space. It pushes aside a large amount of water. The water pushes back with enough force to hold the boat up. This upward push is called buoyancy.

Archimedes' Discovery

Over 2,000 years ago, a Greek scientist named Archimedes figured out why things float. He discovered that an object in water is pushed up by a force equal to the weight of the water it pushes aside. If a boat pushes aside water that weighs more than the boat itself, the boat floats.

Shape Matters

A solid ball of steel sinks because it pushes aside only a little water. But the same steel shaped into a bowl floats because it pushes aside much more water. Boats are designed with wide, hollow hulls to push aside lots of water. If a boat gets a hole and fills with water, it sinks because it can no longer push aside enough water.

Fun Facts

• A cruise ship can weigh over 200,000 tons and still float because of its huge hull shape.
• Concrete can float too if shaped into a boat. There are actually concrete ships in the world.
• Submarines control whether they float or sink by filling or emptying tanks with water.

Did You Know?

The legend says Archimedes discovered buoyancy while taking a bath. He noticed the water level rose when he got in. He was so excited that he jumped out and ran through the streets shouting Eureka, which means I found it!