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# Why does a heavier solid float on water?

Why does a heavier solid i.e. a plastic float on water?

An object floats or sinks in water depending upon the weight of the body and the weight of water displaced by the immersed part of the body. If the weight of the body is greater than the weight of water displaced by it, then it will sink.

If you feel that the weight of the body must be greater than an equal volume of water, and it does not sink, there must be a reason. This is what happens in the case of a ship. The ship is made up of steel. If you put a steel ball or a nail, it sinks. But when the steel is flattened and then shaped in to a boat, it floats. Why?

Because here the average density, which includes the cavity of the boat,  becomes less than the weight of water displaced. You can easily see that the ship will sink if water is allowed to enter into the cavity.

You can experiment with a steel bowl too. The bowl will float on water, it water is not allowed to enter the cavity.

So, it’s not just the density of the material, it is the average density that counts.

If the object is made in the shape of a bowl or a ship, water is not allowed to enter inside, and the weight of the ship is maintained less than the weight of water displaced by it.

Also refer to

http://en.wikipedia.org/wiki/Buoyancy

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