Science Projects And Inventions

YOU  NEED:

• A 5-Paisa Coin
• A bowl filled with water
• A paper clip
• Liquid detergent

The 5 paisa coin has aluminum as an alloy. It is so light that it can be made to float in water. Now fill a bowl with water. Once the water is still, balance a yen on a paper clip and carefully lower the yen to the surface of the water. It will float. Now let a drop of liquid detergent fall on the water- The yen will sink instantly.

HOW DOES IT WORK?

The surface of water can support objects that would normally sink. This is known as water's "surface  tension." Here water molecules attract each other. Water molecules attract each other. Molecules on the surface are always attracted to those beneath them. And as such the water molecules hold on to each other and prevent other objects from entering the water's surface. If you want an object to float on the surface of the water, it has to be light and made up of molecules that are called "hydrophobia" which repel water molecules. Metals like aluminum are hydrophobic. The water's surface tension is greatly reduced once a drop of liquid detergent is put in the water. Interestingly, the molecules that detergents are made of are hydrophobic (which repel water) on one end while the other end is "hydrophilic," (which attract water). The hydrophilic ends point inwards and hydrophobic ends point outwards forming a thin film on the surface of the water. The detergent molecules do not attract other so strongly and come in the way of the water molecules in the surface too. The coin sinks because the surface tension is reduced.