Learning Objectives

• Define a longitudinal wave and identify it as a type of mechanical wave.

• Describe how particles move when a longitudinal wave passes through a medium.

• Differentiate between compressions and rarefactions in a longitudinal wave.

• Explain how wave energy affects its compressions and rarefactions.

• Recognize earthquake P waves as an example of longitudinal waves.

Key Vocabulary

Longitudinal Wave

A mechanical wave where medium particles vibrate parallel to the direction the wave travels.

Mechanical Wave

A wave that requires a medium, which is the matter it travels through, to transfer energy.

Compression

The part of a longitudinal wave where particles of the medium are crowded closely together.

Rarefaction

The part of a longitudinal wave where the particles of the medium are spread farther apart.

P Waves

Longitudinal earthquake waves that pass through underground rocks in all directions away from the disturbance.

What Is a Longitudinal Wave?

• A longitudinal wave is a mechanical wave that travels through a medium.

• The medium's particles vibrate parallel to the direction the wave travels.

• A Slinky spring toy is a great example of this wave.

• Its coils move back and forth along the spring's length.

Compressions and Rarefactions

Compressions

• Compressions are the parts of a longitudinal wave where particles are crowded together.

• These are areas of high pressure and density within the wave's medium.

• A wave with more energy will have particles that are packed more tightly.

Rarefactions

• Rarefactions are the parts of a longitudinal wave where particles are spread apart.

• These are areas of low pressure and density within the wave's medium.

• A wave with more energy will have particles that are spread farther apart.

P Waves: An Example of Longitudinal Waves

• Earthquakes provide a powerful, real-world example of longitudinal waves.

• Earthquakes cause longitudinal waves called P waves, or primary waves.

• These are the first waves to be detected from an earthquake.

• P waves cause underground rock particles to move back and forth.

Common Misconceptions

Summary

• In longitudinal waves, particles vibrate parallel to the direction of wave motion.

• They are mechanical waves and require a medium like a solid, liquid, or gas.

• They consist of compressions and rarefactions.

• More energy results in more intense compressions and rarefactions.