Download Getting to Know: Types of Waves

Getting to Know: Types of Waves
If you’ve ever been in an earthquake, it can be a frightening experience. Everything shakes for
a few moments. Pictures hanging on the wall may sway from side to side, and knick-knacks
on a shelf might fall to the floor. The energy that moves through Earth’s crust can move in
different ways. Sometimes earthquakes shake the ground back and forth, jarring everything
for a second or two. At other times it feels like energy is rolling by underneath you, similar to
how it feels to stand on a boat being tossed in the ocean!
What happens during an earthquake?
What you feel during an earthquake are waves. A wave is a disturbance caused by a vibration that carries energy away from the source. Some waves require a medium, or matter through which they move. Because substances are made of particles, waves cause the particles to move in a coordinated way. Although particles may move around, they will always return to their original position after the wave passes.
As a wave propagates from one location to another, it can cause particles to move either forward and then back or up and down. A longitudinal wave is a wave in which the particles move in a direction parallel (forward and back) to the direction of the wave’s motion. A transverse wave, on the other hand, is a wave in which the particles move in a direction perpendicular (up and down) to the wave.
Ocean waves cause water molecules to
move back and forth.
Misconception 1: I thought water waves carried water across the ocean.
Wave energy travels through the ocean, but it does not transport water molecules from
one place to another. In other words, both transverse and longitudinal waves cause
particles to move—but their overall position doesn’t change. Whether they move up
and down or back and forth, they always return to their original location.
Concept: Types of Waves
Getting to Know
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Earthquakes are caused by seismic waves. These waves travel through Earth’s crust. Earth’s crust is solid, but it is still made up of particles that can vibrate when a wave passes through it. Ocean waves are very similar to seismic waves. However, water waves are caused by wind blowing across the water’s surface rather than by a release of energy in Earth’s crust. Water waves also move through liquids rather than solids.
Can waves move through the air?
Waves such as sound waves can move through gases, like the air. Sound waves are longitudinal waves that compress and expand matter as they travel. Sound waves result from the physical vibration of an object. When a person plays a guitar, for instance, the vibration of the string causes the particles in the air to move back and forth. The energy from the plucked string travels through the air as the particles vibrate and collide with one another. Eventually, the sound waves pass into someone’s ear, where moving air particles bump against the eardrum. You can hear the sounds coming from a radio or TV because these devices have speakers. The speakers vibrate rapidly to produce sound waves.
Playing a guitar produces waves
called sound waves.
Radio and TV broadcasts also rely on electromagnetic waves, which radiate from a source and
do not require a medium to travel. Electromagnetic waves are transmitted by radio towers,
television stations, or satellites. They can travel through empty space, because they do not
need particles of matter to propagate them. Gamma rays, x-rays, and ultraviolet light also
travel in electromagnetic waves. We rely on electromagnetic waves to see; light energy is an
electromagnetic wave that radiates from the Sun and other energy sources.
Misconception 2: Light waves are different than other types of waves, because
they don’t look like ocean waves.
Light waves do not require a medium to move through, but the energy does move in a
wave pattern. The distance between each wave, however, is so tiny that you don’t notice
the movement of the energy as you do when you watch energy move through the ocean.
In this lesson, you will learn more about seismic, sound, and electromagnetic waves.
Concept: Types of Waves
Getting to Know
www.discoveryeducation.com
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© Discovery Education. All rights reserved.
Discovery Education is a subsidiary
of Discovery Communications, LLC.