Longitudinal Wave
Jean Brainard, Ph.D.
Say Thanks to the Authors
Click http://www.ck12.org/saythanks
(No sign in required)
To access a customizable version of this book, as well as other
interactive content, visit www.ck12.org
CK-12 Foundation is a non-profit organization with a mission to
reduce the cost of textbook materials for the K-12 market both
in the U.S. and worldwide. Using an open-content, web-based
collaborative model termed the FlexBook®, CK-12 intends to
pioneer the generation and distribution of high-quality educational
content that will serve both as core text as well as provide an
adaptive environment for learning, powered through the FlexBook
Platform®.
Copyright © 2015 CK-12 Foundation, www.ck12.org
The names “CK-12” and “CK12” and associated logos and the
terms “FlexBook®” and “FlexBook Platform®” (collectively
“CK-12 Marks”) are trademarks and service marks of CK-12
Foundation and are protected by federal, state, and international
laws.
Any form of reproduction of this book in any format or medium,
in whole or in sections must include the referral attribution link
http://www.ck12.org/saythanks (placed in a visible location) in
addition to the following terms.
Except as otherwise noted, all CK-12 Content (including CK-12
Curriculum Material) is made available to Users in accordance
with the Creative Commons Attribution-Non-Commercial 3.0
Unported (CC BY-NC 3.0) License (http://creativecommons.org/
licenses/by-nc/3.0/), as amended and updated by Creative Commons from time to time (the “CC License”), which is incorporated
herein by this reference.
Complete terms can be found at http://www.ck12.org/terms.
Printed: January 28, 2015
AUTHOR
Jean Brainard, Ph.D.
www.ck12.org
C HAPTER
Chapter 1. Longitudinal Wave
1
Longitudinal Wave
• Describe a longitudinal wave.
• Identify compressions and rarefactions of a longitudinal wave.
• Define P waves.
You’ve probably played with Slinky spring toys like these. They’re simple toys, but they can move in very interesting
ways. Pushing in on the end of a spring toy, for example, gives it energy that moves through the spring in a
longitudinal wave.
What Is a Longitudinal Wave?
A longitudinal wave is a type of mechanical wave. A mechanical wave is a wave that travels through matter, called
the medium. In a longitudinal wave, particles of the medium vibrate in a direction that is parallel to the direction
that the wave travels. You can see this in the Figure 1.1. The person’s hand pushes and pulls on one end of the
spring. The energy of this disturbance passes through the coils of the spring to the other end. You can see a video of
a longitudinal wave in a spring at this URL: http://www.youtube.com/watch?v=ubRlaCCQfDk .
MEDIA
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/82386
1
www.ck12.org
FIGURE 1.1
Compressions and Rarefactions
Notice in the Figure 1.1 that the coils of the spring first crowd closer together and then spread farther apart as the
wave passes through them. Places where particles of a medium crowd closer together are called compressions, and
places where the particles spread farther apart are called rarefactions. The more energy the wave has, the closer
together the particles are in compressions and the farther apart they are in rarefactions.
P Waves
Earthquakes cause longitudinal waves called P waves. The disturbance that causes an earthquake sends longitudinal
waves through underground rocks in all directions away from the disturbance. P waves are modeled in the Figure
1.2.
FIGURE 1.2
Q: Where are the compressions and rarefactions of the medium in this model of P waves?
A: The compressions are the places where the vertical lines are closest together. The rarefactions are the places
where the vertical lines are farthest apart.
Summary
• A longitudinal wave is a type of mechanical wave, or wave that travels through matter, called the medium. In
a longitudinal wave, particles of the medium vibrate in a direction that is parallel to the direction that the wave
travels.
2
www.ck12.org
Chapter 1. Longitudinal Wave
• Places where particles of the medium crowd closer together are called compressions. Places where particles
of the medium spread farther apart are called rarefactions.
• Earthquakes cause longitudinal waves called P waves, which pass through underground rocks.
Explore More
Watch the animation of a longitudinal wave at the following URL, and then answer the questions below. http://w
ww.phy.hk/wiki/englishhtm/Lwave.htm
1. In which direction is the wave traveling?
2. What does the red line represent?
3. Describe how the red line moves.
Review
1. What is a longitudinal wave?
2. Draw a sketch of a longitudinal wave. Use arrows to show the direction of the wave and the direction of the
vibrating particles of the medium. Add labels to identify the compressions and rarefactions.
3. Describe P waves.
References
1. Christopher Auyeung. Diagram of a longitudinal wave . CC BY-NC 3.0
2. Christopher Auyeung. Primary waves are longitudinal waves . CC BY-NC 3.0
3