# Waves: Overview

Editor: Thomas Riggs
Date: 2018
From:
Publisher: Gale, a Cengage Company
Document Type: Topic overview
Length: 1,140 words
Content Level: (Level 3)

Full Text:
Page 97

# Waves: Overview [Includes Video]

When we think of waves, we usually think of the kind we see in the ocean. But waves are all around us. Invisible waves in the air carry sound, heat, and other forms of energy. A wave can be defined as a disturbance that transmits energy from one place to another.

There are two main types of waves: mechanical and electromagnetic. Mechanical waves move through a physical substance, or medium, such as air or water. When you pluck a guitar string, for example, you create a mechanical wave as the string vibrates back and forth. This vibration disturbs the air molecules around the guitar. Eventually, this disturbance causes your eardrum to vibrate. These vibrations are then converted to an electrical signal that travels to your brain, and your brain interprets it as sound.

Electromagnetic waves are different from mechanical waves in that they move through an electric and magnetic field. They can move through a physical medium, such as water, but they can also move without a medium, making them able to travel through the emptiness of space. The light that travels to Earth from the Sun is an example of an electromagnetic wave. Heat from the Sun also travels through electromagnetic waves. The only two types of electromagnetic waves that can be sensed by people are visible light and heat; all other types are invisible. Instead, technology is used to detect these invisible waves and convert them into information.

## Features of Transverse and Longitudinal Waves

Waves travel in two basic forms: transverse and longitudinal. Transverse waves move up and down along an S-shape Page 98 curve. The vibrations of a guitar string are an example of a transverse wave. Before you pluck a guitar string, it is at equilibrium. After you pluck the string, it moves back and forth across this equilibrium position. The farthest it moves from equilibrium in the positive direction is called the wave's crest. The farthest it moves from equilibrium in the negative direction is its trough. The length between each crest or trough is known as the wavelength.

The sound from a plucked guitar string starts in the form of a mechanical wave. © 2018 CENGAGE®. © 2018 CENGAGE®.

Longitudinal waves follow a coil shape. An example of a longitudinal wave is sound traveling through air. Unlike transverse waves, longitudinal waves do not have crests and troughs. Instead, they have compressions and rarefactions. Compressions occur when the coils are closer together, creating higher pressure. Rarefactions occur when the coils are farther apart, creating lower pressure. The wavelength of a longitudinal wave is the distance between two compressions in a row or two rarefactions in a row.

## Frequency and Amplitude

Scientists measure waves using frequency and amplitude. The frequency is how many wavelengths occur in a given period. A low-frequency wave might have only one or two Page 99 wavelengths per second. A high- frequency wave might have trillions of wavelengths per second. When the period is one second, the frequency is measured in units called hertz (Hz). For example, if a sound wave cycles through five wavelengths per second, its frequency is 5 Hz.

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WORDS TO KNOW
Amplitude:
A measurement of the change in pressure caused by a sound wave. A high-amplitude sound wave will create a lot of pressure, producing a sound that is louder and more forceful than a low-amplitude sound wave.
Compression:
A region of a longitudinal wave in which the particles are close together.
Crest:
The point on a transverse wave farthest from equilibrium in the positive direction.
A wave that does not require a physical medium to travel. Light and heat are examples of electromagnetic waves.
Electromagnetic spectrum:
The range of frequencies or wavelengths that electromagnetic radiation can travel over. X-rays and ultraviolet light have very short wavelengths. Radio waves and microwaves have longer wavelengths.
Frequency:
The number of wavelengths, or wave cycles, a wave passes through in a given period.
Longitudinal wave:
A coil-shaped wave in which the particles move in the same direction as the wave.
Mechanical wave:
A wave that requires a physical medium to travel, such as sound.
Medium:
A material through which a wave can travel.
Rarefaction:
A region of a longitudinal wave in which the particles are far apart.
Transverse wave:
An S-shape wave in which the particles move perpendicular to the direction of the wave.
Trough:
The point on a transverse wave farthest from equilibrium in the negative direction.
Wavelength:
The length of one wave cycle.

When you pluck a guitar string, the pitch of the sound you hear depends on the frequency of the wave that is created. Page 100 The higher the note you play, the faster the string vibrates. Higher notes create shorter, more rapid waves. Your brain interprets these higher-frequency waves as having a higher pitch. Lower notes vibrate more slowly, creating longer waves. Your brain interprets these lower-frequency waves as having a lower pitch.

Compression and Rarefaction in a Longitudinal Wave © 2018 CENGAGE®. © 2018 CENGAGE®.

Amplitude is a measure of the amount of energy a wave carries. In the example of the guitar, when you pluck a string with great force, the wave it creates is taller, or has a higher amplitude. Your brain interprets high-amplitude sound waves as being loud. If you pluck the string softly, the wave it creates is shorter, or has a lower amplitude. Your brain will interpret these low-amplitude sound waves as being soft.

## Electromagnetic Spectrum

Much of the technology we use today relies on electromagnetic waves, or electromagnetic radiation. Televisions, Wi-Fi, Bluetooth, and microwave ovens all rely on electromagnetic waves to work. Scientists classify electromagnetic waves according to their frequency. When we put all of the electromagnetic wave frequencies in order from lowest to highest, it is called the electromagnetic spectrum.

Electromagnetic Spectrum