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Why don't ships sink?
Ships don't sink because they take up a lot of space for their weight, and they push water away to make room for themselves.
When a ship goes into water, it pushes the water aside. The pushed water pushes back up on the ship with a force. This is called buoyancy. The more water a ship pushes away, the stronger the buoyancy it gets.
Ships are built hollow, like a bowl. Because they are hollow, they take up a huge amount of space for their weight. This means they push away a lot of water and get a strong push back up. If you threw a solid iron ball into water, it would sink right away, because it is small and solid, so it pushes away only a little water.
A nail sinks, but a huge ship does not. The reason is shape and empty space, not weight. A ship pushes away as much water as the part of it under the water, so it gets a push back up equal to its own weight, and floats steadily.
If water gets inside a ship, its weight goes up and the empty space inside disappears. Then the push from the water isn't enough, and the ship can sink. That is why ship hulls are built strong and able to keep water out.
Quick facts
- Water pushes up on everything that goes into it, and this is called buoyancy.
- Ships are built hollow, so they take up a lot of space for their weight.
- Things that take up more space push away more water and get a stronger push back up.
- If a ship pushes away water equal to its own weight, it stays steady in the water.
- If water gets inside a ship, its weight goes up and it can sink.
- Archimedes is the scientist who discovered buoyancy.
Check what you remember
4 questions — all of them come from the quick facts above. There is no score and no wrong turn.
1. What is the force called that pushes objects up in water?
2. Why do ships take up so much space?
3. Who discovered buoyancy?
4. What happens if water gets inside a ship?
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