-: DETERMINING THE SURFACE TENSION OF WATER :-

Surface tension is a force that occurs at the surface of a liquid. The surface of a liquid due to the inward pull of its molecules acts like a stretched elastic membrane. This membrane can support light objects. For example, a blade can float on the surface of water. You can measure the surface tension of water by this simple project.

MATERIALS REQUIRED

• To measure surface tension, you have to make a balance device. For making the balance, take a wooden block and glue a wooden strip at Its center. Make the beam of the balance by using another wooden strip and using a pin as a pivot. 

• Take the iron ring and make a small bag of cloth. Tie three threads to make a pan of the balance.
• Take the plastic sheet and put a tiny hole in the centre with a needle. Tie a knot in a thread and use it to suspend the plastic sheet from one end of the balance.

• Use small nails on the other end to balance the plastic sheet. 

• Now, bring the bowl full of water and put it under the plastic sheet in such a way that it just touches the surface of water.You will see that the balance is disturbed. 

•  Now, add small nails in the pan until the plastic sheet suddenly breaks away from the surface of water. This extra weight is nothing but a measure of the surface tension of the water - the force with which it attracts the plastic.
• You can repeat the experiment by using mustard oil, kerosene oil, alcohol, etc. instead of water and measure their respective surface tensions also. 

More Example :-

• A razor blade or a sewing needle can be made to float on the surface of water, although these things are heavier than water. Put the blade or needle on a piece of blotting paper and then place it gently on the surface of water in a glass. The blotting paper soon gets drowned into the water and the blade or needle remains floating on the surface of water. This is due to surface tension.

• The nib of a pen is slit at the tip to provide the continuous flow of ink by surface tension.