Compression Wave: Definition & Overview

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  • 0:00 The Importance of Waves
  • 0:25 Slinky Example
  • 1:07 Features of Longitudinal Waves
  • 2:15 More Examples of…
  • 3:11 Lesson Summary
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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

This lesson will define longitudinal (or compression) waves, discuss the names for various features and parts of a longitudinal wave, and go through some examples of longitudinal waves in the world. A short quiz will follow.

The Importance of Waves

Waves carry energy, and in the case of earthquake waves, they carry huge amounts of energy. The first thing you feel when an earthquake hits is a longitudinal wave, and every sound you hear is a longitudinal wave. Waves are everywhere in nature and understanding them is an important part of explaining the world as a whole.

Slinky Example

Longitudinal waves, also known as compression waves when describing waves in mechanical terms, are waves where the vibration is parallel to the direction the wave is moving. That might be hard to picture, which is why we need some help from a Slinky.

It looks something like this:

A Longitudinal Wave in a Slinky

A longitudinal wave is what you get if you push a Slinky along its length, sending a pulse down it.

The other type of wave is called a transverse wave. A transverse wave looks something like this.

A Transverse Wave in a Slinky

A transverse wave is a wave where the vibration is at right angles to the direction the wave is moving. That's what you get if you move the Slinky from side to side, sending a wave along it.

Features of Longitudinal Waves

There are a few features we can label on a longitudinal wave, as shown in the diagram onscreen now:

Features of Longitudinal Waves

A compression is the part of the wave (or Slinky) that is pressed together -- this is like the crest or peak of the wave. A rarefaction is the part of the wave (or Slinky) that is the most spread apart -- this is like the trough of the wave.

You can see how these compressions and rarefactions can be considered as crests and troughs if we plot a graph of particle density against position for a (longitudinal) sound wave shown.

Longitudinal Wave Pressure Graph

As you can see from the diagram, the particle density varies in a perfect wave shape. This is how we know that longitudinal 'waves' are really waves.

This diagram allows us to measure another feature of longitudinal waves -- the wavelength. A wavelength is the distance from two similar parts of a wave—from a peak to the next peak or from a trough to the next trough. It is the length of one full wave, one full oscillation. Wherever you measure it, the number should come out the same.

Other Examples of Longitudinal Waves

Most waves in the universe turn out to be transverse waves, but there are a few examples of longitudinal waves.

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