Photoacoustic Doppler effect

The photoacoustic doppler effect is a special way sound waves can be used to study moving objects. It works like this: when a light (like a laser) hits something that is moving, it causes the object to vibrate, just like if somebody had hit it with a hammer or tapped it with their fingertips. Those tiny vibrations create sound waves that travel away from it, and those sound waves can be detected with special machines called microphones. The speed and direction of the object can then be determined based on how the sound waves change as they move away from the object.