See it with fire

The candle flames rise and fall in a pattern. That pattern is compression and rarefaction made visible.

In every version: sound creates alternating zones of compression and rarefaction. The flames make those invisible zones visible.

Sound waves move by squeezing and stretching the particles they pass through. The squeezed regions are called compressions; the stretched regions are rarefactions. Watch them in the visualizer below.

Longitudinal Wave
Compression Rarefaction
Waiting for input

Parameters

Sound is not a sine curve

or

Key terms

When a sound wave moves through a medium, it creates two alternating zones: SPI Exam Topic

Compression
Particles squeezed together
High pressure
High density
tap to see
Rarefaction
Particles stretched apart
Low pressure
Low density
tap to see

Tap each card to learn about the underlying physics.

Pressure
Tap to flip
Pressure
How hard particles push against each other.
Compression: High pressure
Rarefaction: Low pressure
More particles crammed together = more collisions = higher pressure.
dense sparse
Density
Tap to flip
Density
How closely packed particles are in a space.
Compression: More dense
Rarefaction: Less dense
Same particles, different spacing. Nothing was added or removed.

In ultrasound

This is compression and rarefaction happening with an actual ultrasound transducer. SPI Exam Topic

Schlieren imaging makes the invisible pressure waves from an ultrasound scan visible.

Everything you learned on the previous tabs (compression zones, rarefaction zones, pressure differences, density changes) is exactly what's happening every time a sonographer places a transducer on a patient.

Quick check

Look at the pyro board. Where the flames shoot up, the air particles there are:
Concept Recall

When you pushed the piston forward, the particles:
Concept Recall

Drag each label to the correct zone:
Bunched particles
Spread particles
Compression
Rarefaction
Compression zones have ___ pressure.
Concept Recall

In a rarefaction zone, particles are:
Concept Recall

Review Complete

You've finished the compression and rarefaction check-in.