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Boats, canoes, ships, kayaks, and rafts all have one thing in common- they are used for transport on seas and rivers, because they float.
It's easy to figure out that if they are made out of wood they will float, because wood floats in water. However, when you see a huge cargo ship or a cruise-liner that looks like a floating building on the water, you can't help but wonder why this massive chunk of metal doesn't sink.

The Archimedes Principle

A long time ago in ancient Greece, a mathematician named Archimedes was taking a bath. When he got in, a certain amount of water got displaced and overflowed over the rim of the tub.

Buoyancy Definition

Archimedes figured out that if the weight of the object being placed in the water is less that the weight of the water displaced, the object will float. This is known as buoyancy or the Archimedes principle.

How Ships float?

A ship made out of metal is able to remain lighter than the amount of water it displaces, because it is not a complete solid. The very bottom of the ship, called the hull, is hollow and therefore adds support to the ship without adding any mass.

When a ship is fully loaded, there is a maximum amount of weight it can carry before the weight of the ship increases past the amount of water it displaces.

If a ship has excess water during a storm, it is simply pumped back out into the ocean and it's once more safe from sinking.

How Life Jackets work?

Life jackets use buoyancy too. Since your body is mostly water, holding on to a light life jacket is enough to keep you afloat in the deep.

The material inside a life jacket traps air when the jacket is covered in water. This trapped air weighs much less than the water it displaces. So, the life jacket floats and its buoyancy is strong enough to support your weight too.

Things to do -
The next time you are in a swimming pool, try floating. Lie flat on your back and try to keep afloat. You will notice that you are more buoyant when you inhale, than when you exhale. Can you figure out why?
For more such interesting Physics videos and articles visit our Physics for Kids category.

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What is Buoyancy? - Physics for Kids | Mocomi

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Boats, canoes, ships, kayaks, and rafts all have one thing in common- they are used for transport on seas and rivers, because they float. It's easy to figure out that if they are made out of wood they will float, because wood floats in water.

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1. Buoyancy doesn't depend on the volume because ships are big and they float.
2. Some metal objects float because they have air inside.
3. Some heavy objects float (example: boat)
4. Empty objects have air and they float.
5. Wood floats.
6. People float because they have air in their lungs.

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1.If depends on the weight of the object.
2. If the water weighs more than the object, the object floats, but if the water weighs less than the object it sinks.
3. Depending on the material it is made of, an object can sink or float. Metal usually sinks, but a ship floats because it has air in it and a big base.
4. If objects have air in them, they float.
5. Displacement is the movement of water when you put an object in the recipient.
6. The displacement happens because of the volume of the object.