The Doppler Effect: How Motion Changes the Pitch of Sound and Light

Picture a train racing toward you, horn blaring.

As it approaches, the sound waves bunch up, making the pitch higher.

Once it passes, the waves stretch out, dropping the pitch.

This shift isn't just your imagination.

It's the Doppler effect.

And it's why moving objects seem to change their sound as they pass by.

But the Doppler effect isn't limited to sound.

It also affects light.

When a star or galaxy moves toward us, its light shifts to blue, called blueshift.

When it moves away, the light stretches to red, known as redshift.

Astronomers use this cosmic color code to measure the speed and direction of distant galaxies.

Why does this happen?

Imagine throwing pebbles into a pond while walking.

If you walk toward the ripples, they bunch up; if you walk away, they spread out.

Sound and light waves behave the same way.

The motion of the source or observer changes how frequently the waves hit your ears or eyes, altering

pitch or color.

The Doppler Effect isn’t just a cool science fact— it’s practical.

Police use it in radar guns to catch speeding cars.

Doctors use it in ultrasounds to track blood flow.

And astronomers rely on it to map the universe’s expansion.

So next time you hear a siren change pitch, remember: you’re experiencing a fundamental law of physics in

real time!