Materials Required:
- Onion
- Cutting board
- Knife
Procedure:
- Set a small onion on a cutting board or plate. Ask one of your parents to slice the onion in half with a sharp knife.
- Hold the cut onion next to your nose and take a little sniff. You will begin to shed tears. Do you know what causes this reaction?
This is what happens:
Onions contain a strong-smelling oil inside their cells. When you cut into the onion, some of this oil forms a vapour which goes into the air, and is detected by your nose. The nerves inside your nose are very sensitive to the vapour.
At times when you are not weeping, your eyes still have small amounts of tears, which help to keep them clean and moist. The tears flow over your eyes, then into small openings in the corners of your eyes. From here, the fluid is routed into your nose. When you cry, however, the tiny canals cannot handle the great amount of liquid, and tears roll down your face in big drops.
