Transverse and Longitudinal Waves

Transverse and Longitudinal Waves

Middle School

​

Learning Objectives

• Describe how waves are responsible for the transfer of energy from one place to another.

• Compare and contrast the distinct characteristics of longitudinal and transverse waves.

• Identify and label the main parts of both longitudinal and transverse waves.

• Explain the difference between mechanical and electromagnetic waves based on their need for a medium.

Key Vocabulary

​

Longitudinal Wave

A wave where particles vibrate parallel to the direction of the wave's energy transfer.

​

Transverse Wave

A wave where particles vibrate perpendicular to the direction that the wave's energy is traveling.

​

Compression

An area in a longitudinal wave where the particles of the medium are crowded together.

​

Rarefaction

An area in a longitudinal wave where particles of the medium are spread farther apart.

​

Crest

The highest point of a transverse wave, representing the maximum upward displacement from the rest position.

​

Trough

The lowest point of a transverse wave, representing the maximum downward displacement from the rest position.

​

​

What Are Transverse Waves?

• Particles in a transverse wave vibrate perpendicularly to the direction of the wave’s energy.

• ​Imagine a rope wave: the rope moves up and down as the wave moves forward.

• The highest points of a wave are called crests, and the lowest points are troughs.

• Light, radio, and water waves are all examples of transverse waves.

Multiple Choice

In a transverse wave, how do the particles of the medium move relative to the direction of energy transfer?

• Parallel to the direction of energy transfer.

• Perpendicular to the direction of energy transfer.

• In a circular motion.

• They do not move at all.

​

​

What are Longitudinal Waves?

• Particles vibrate parallel to the direction of the wave's energy.

• ​Think of a Slinky moving back and forth in the same direction.

• This creates crowded compressions and spread-out areas called rarefactions.

• Sound waves and earthquake P-waves are examples that need a medium to travel.

Multiple Choice

What are the areas called in a longitudinal wave where particles of the medium are crowded together?

• Crests

• Troughs

• Compressions

• Rarefactions

​

​

Comparing Wave Characteristics

Wavelength

• ​This is the distance between two identical points on successive waves.

• ​​In a transverse wave, it is measured from crest to crest or trough to trough.

• ​In a longitudinal wave, it is the distance between two compressions or rarefactions.

Amplitude

• ​This relates to the amount of energy that a particular wave carries.

• ​​For a transverse wave, it is the distance from the rest position to a crest or trough.

• ​For a longitudinal wave, it relates to how packed particles are in compressions.

Multiple Choice

How is the wavelength of a longitudinal wave measured?

• From the crest of one wave to the crest of the next.

• From the highest point to the lowest point of the wave.

• From the start of one compression to the start of the next compression.

• From the midpoint of a rarefaction to the midpoint of the next crest.

​

Common Misconceptions

Misconception	Correction
Waves transfer matter from one place to another.	Waves transfer energy, not matter. Particles return to their rest position.
All waves require a medium to travel.	Only mechanical waves need a medium. Electromagnetic waves can travel through a vacuum.
Sound can travel through space.	Sound is a mechanical wave and requires a medium to travel through.

Multiple Choice

A P wave from an earthquake travels through underground rock. What type of wave is this and how do the rock particles move?

• Transverse; the particles move up and down as the wave travels forward.

• Longitudinal; the particles move back and forth in the same direction the wave travels.

• Transverse; the particles move back and forth in the same direction the wave travels.

• Longitudinal; the particles move up and down as the wave travels forward.

Multiple Choice

If you drop a rock in a pond, waves spread out. Which statement best explains why a leaf floating on the water bobs up and down but does not travel to the edge of the pond?

• The wave is a longitudinal wave, pushing the leaf up.

• The leaf is too heavy to be carried by the wave.

• The wave transfers energy through the water, but it does not carry the water or the leaf with it.

• The wind is holding the leaf in place against the wave's force.

Multiple Choice

A musician plays a loud note and then a soft note on a flute. Both notes travel to a listener as sound waves. What is the primary difference between the loud sound wave and the soft sound wave?

• The loud wave has a longer wavelength than the soft wave.

• The loud wave travels faster than the soft wave.

• The loud wave has a greater amplitude (tighter compressions) than the soft wave.

• The loud wave is a transverse wave, while the soft wave is a longitudinal wave.

Multiple Choice

Which of the following best describes the amplitude of a wave? 

• The distance between two consecutive crests of the wave.

• The number of waves passing a point per second.

• The distance from the rest position to a crest or trough in a transverse wave, or how compressed particles are in a longitudinal wave, relating to the wave’s energy

• The speed at which the wave travels through the medium. 

​

Summary

• Waves are disturbances that transfer energy, not matter.

• Transverse waves vibrate perpendicularly, while longitudinal waves vibrate parallel to the energy direction.

• Amplitude measures a wave's energy, and wavelength is the distance between identical parts.

• Mechanical waves need a medium; electromagnetic waves can travel through a vacuum.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

• 1

• 2

• 3

• 4