Effect of Air Pressure in Working of a Straw

Aim:

The aim of this science fair project is to understand the effect of atmospheric pressure in the working of a straw.

Materials required:

  1. A straw.
  2. A glass jar with a lid.
  3. Some clay.

Procedure:

  1. Fill water in the jar.
  2. Make a hole in the lid and close it.
  3. Put the straw through the hole and use clay to seal the space around the straw.
  4. Suck on the straw. The water will not come out of the jar no matter how hard you try.
  5. Remove the lid and stick the straw into the water again and suck on it. This time the water will flow into your mouth.

Scientific explanation:

Straws work with the effect of change in air pressure. Normally when you put a straw in a bottle or glass and suck, you reduce the air pressure in your mouth. But air pressure outside is still the same. This higher air pressure will push down on the water and force it to climb up the straw into the low pressure region. When you have the lid sealed, the outside air cannot push down on the liquid to push it up the straw. Hence no matter how hard you suck, you will not be able to get the water into your mouth.