Why does a needle float in water?

Answer 1

It doesn't actually float, since its density is greater than water. It is kept from sinking by the surface tensionof the water. This phenomenon is created by the formation of polar bonds between the surface water molecules. To make this happen, the needle must be carefully placed on the calm surface of the water, usually held in a container like a glass tumbler (easier to keep the surface calm, than in a wider container like a bowl).

If you wish to prove this principle, here is a very successful method:

1. Place a piece of tissue, slightly larger than the needle is long, flat on the surface of the water.

2. Lay the needle carefully on the tissue.

When the tissue becomes saturated and sinks away from the needle, the needle will remain on the surface of the water. If you wish, once the tissue sinks, It can be removed (carefully) from the system with tweezers. Then you can amaze your friends with your imponderable, impossible feat, of floating a needle. This method will work with a paper clip as well. Any metal object, with smooth surfaces and not too heavy, may be used.

Tip: shape matters. Common pins have been used, but often they won't work because their heads breach the tension membrane.

More Information:

Surface tension. The needle is thin and light, so it just lays on the water. Surface tension is what we call a thin flexible membrane, formed by the polar bonding of surface water molecules, to each other. like a water bed for very light objects.

Answer 2

For something to float in water, it must be less dense than the water itself or filled with air. Obviously not filled with air, a needle is less dense than water, depending on the size of the needle.