Sonic boom

A sonic boom is the sound you hear when something is moving faster than the speed of sound. Imagine you are throwing a pebble into a pond. As the pebble travels across the water it makes a series of waves. The waves move away from the spot where you threw the pebble. Now imagine a jet plane flying very fast in the sky - like a pebble in the pond, it has to push the air out of the way as it moves so it makes a series of waves in the air. These waves take time to travel away from the jet and when they finally reach your ears, you hear it as a "boom" sound! That is a sonic boom.