# How does a cruise ship stay afloat?

## Why don't ships sink in the water even though they are much heavier than humans?

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### If I throw a piece of solid metal into the water, it goes under. A ship that is made of tons of steel and is actually much heavier than the piece of metal that floats. Why is that? Sabine from NeuĂ¶tting would like to know that.

The fact that a ship weighing thousands of tons can swim can be explained by the principle of Archimedes. Archimedes was a Greek mathematician who first discovered:

You can carry your weight more easily underwater than on earth. This is due to buoyancy, a force that is directed upwards. The buoyancy experienced by a floating body in a liquid is as great as the weight of the displaced liquid.

A body swims in water when its weight corresponds to that of the water it displaces. You know that when you step into a bathtub that is filled to a certain level, the water rises as soon as you sit in it. The edge climbs up a little. This water is what you have displaced through your body.

For example, if you throw a steel ball into the water, this ball has a certain surface area and displaces a certain amount of water. If you now build a hollow body from the same amount of steel, then it has a much larger surface, because you leave it hollow on the inside. You can build a larger surface and that in turn displaces more water. Due to the greater water displacement, this hollow body then has the buoyancy necessary for swimming.

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