Why do my hands make noise when I clap?

Answer

Dear Diederik,

When you hear something, it means that you are picking up rapid fluctuations or vibrations in air pressure with your ears. You can compress air, you notice that when you put your finger on the end of a bicycle pump and then press the pump. If you hang a weight on the bicycle pump, you could make this weight oscillate for a while by giving it a tug. On a small scale, air is like a very fast spring, and the mass that vibrates is the mass of the air itself. This resilience allows waves to propagate through the air. When you clap your hands there is a collision between your two hands which causes a shock. This shock creates a high pressure around your hands. This pressure causes the air to vibrate. These vibrations propagate at the speed of sound and your ears pick up on these vibrations. Your brain then gives meaning to these vibrations using signals it has previously picked up with your senses and stored in memory. You can clap with one hand, for example by knocking your hand against a door. Hollow objects can transmit vibrations better than solid objects. That’s why guitars and violins are hollow inside. You can also clap a little by hitting your fingers hard against your palm.