What Causes the 'Doppler Effect' and How Is It Used in Real Life?

Imagine you're sitting on a park bench, and a fire truck is zooming past you with its siren blaring. When the truck comes toward you, the sound waves get squished together, making the pitch seem higher. Once it passes by and moves away, the sound waves stretch out, making the pitch lower. This change in pitch is called the Doppler Effect. It’s like when a friend runs toward you while calling your name, their voice sounds a bit sharper than when they run away.