Science Project “How to Float a Metal Coin” Complete School Projects on Air, Water, Weather and Temperature for Class 8, 9, 10 and 12 Students.

How to Float a Metal Coin

Materials Required:

1. A 1-yen coin (Japanese currency)
2. A bowl filled with water
3. A paper clip
4. Liquid detergent

The 25-paisa coin has aluminium 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. 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. 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 “hydrophobic” which repel water molecules. Metals like aluminium 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.