How do boats float?

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HAVE you ever wondered why ships and boats that carry tonnes of weight can float in water but you can’t walk on water? Boats are a brilliant example of how science solves a simple problem. More than two thirds of Earth’s surface is covered in water so it’s just as well that science helps us take to the waves. How exactly do boats do their stuff?

The science behind floating was first studied by an ancient Greek scientist named Archimedes. He figured out that when an object is placed in water, it pushes enough water out of the way to make room for itself.

This is called displacement. Have you ever experienced displacement? If you got into the bathtub and the water level went up? That’s displacement. When you got into the tub, water got out of your way to make room for you, so the water level in the tub got higher.

When an object enters water, two forces act upon it. There’s a downward or gravity force that’s determined by the object’s weight. There’s also an upward force (buoyancy) that are determined by the weight of the water displaced by the object.

An object will float if the gravitational (downward) force is less than the buoyancy (upward) force. So, in other words, an object will float if it weighs less than the amount of water it displaces. This explains why a rock will sink while a huge boat will float.

The rock is heavy, but it displaces only a little water. It sinks because its weight is greater than the weight of the small amount of water it displaces.