Doppler effect

The Doppler effect was invented by a man who's name is Christian Doppler. He came up with the idea in 1842. It is when a car comes by holding down its horn. The pitch goes up and back down. Whats happens is when the car starts moving and making sound, the sound waves in front of the car get compressed. The sound waves at the back of the car spread out more. That is why the pitch goes up, and goes back down. The Doppler effect has many uses to it. We use it to predict weather, using microwaves, or electromagnetic waves. We also use it in LifeAlert systems.