The Doppler Effect

Have you ever heard the tell-tale sound

Of a distant ice cream truck,

And you run outside with your crumpled bills

As you thank your precious luck?


You can hear that one familiar tune

That you’ve heard so many times,

And you know the truck’s approaching you,

For the pitch is bending high.


You take your prize with the gumball eyes

While the driver turns to go;

As he drives away the song acquires

A slightly eerie tone.


For the farther and farther down the road

The truck so quickly goes,

The lower and lower and lower than low

The song’s pitch seems to go.


What is the cause of this warping sound,

The truck’s lamenting moan?

What grief resides in its bending howl?

What is its hidden woe?


Does it wish to be a taco truck?

Is it tired from its load?

Does it curse its fate forever stuck

On a long, monotonous road?


Well, the truth of it is much profound,

But it’s not what you’d expect;

This bending pitch and warping sound

Is called the Doppler effect!


The ice cream truck approaches you

While on the curb you wait;

Meanwhile its fun and quirky tune

Ripples towards you in waves.


The moving truck gives every wave

A helpful, forward push;

Each wave has a shorter path to take,

So they reach you squashed and smooshed.


And as the waves compress, the frequency

Appears to rise,

And frequency is pitch, you see,

So the pitch appears to climb.


And the opposite of this is true:

As the truck rumbles away,

Each wave takes longer to get to you,

So the pitch bends down and fades…


This effect that Mr. Doppler found

Works for any kind of wave;

Radio, water, light, or sound,

It happens all the same.


Essentially, this Doppler Effect

Is a trusty speed radar;

Police even use it to detect

The speed of motor cars.


It’s also used in medicine

For measuring blood flow;

It can uncover evidence

Of heart defects unknown.


But even crazier is its use

In the field of astronomy;

It helps astronomers deduce

The movement of galaxies.


It’s been well used to supplement

And enrich our understanding;

According to the Doppler effect

The universe is expanding!