Unit 14 Lesson 1 - WordPress.com · 14.11.2017 · Unit 14 Lesson 1 What Is Sound? Waves of Sound...

Unit 14 Lesson 1 What Is Sound?

Waves of Sound

Copyright © Houghton Mifflin Harcourt Publishing Company


Waves of Sound


• A wave is a disturbance that transmits energy. There are some waves that you cannot see.

• Vibrations are the back-and-forth movements of an object.

• Sound is a series of vibrations traveling in waves.

14.1 VIDEOS/Science - Transmission of Sound - trimmed 1.mp4


Waves of Sound



Waves of Sound


• All sound vibrations travel in compression waves.

• As a compression wave moves, molecules of air or other matter are pushed together, or compressed.

• The molecules spread apart, and sound energy moves away from its source as this bunching and spreading of molecules repeats.


Waves of Sound



It Sounds Like …


• Pitch and volume are two ways to measure sound.

• The highness or lowness of a sound is its pitch.

• Frequency is the number of vibrations that occur during a unit of time. High-pitched sounds have high frequencies. Low-pitched sounds have low frequencies.

14.1 VIDEOS/001 - Pitch and Frequency.mp4


It Sounds Like …


• The loudness of a sound is its volume. Volume is measured in units called decibels, abbreviated dB.

• The softest sounds humans can hear are near 0 dB. The humming of a refrigerator is about 40 dB, while heavy city traffic is about 85 dB.

• Listening to high-decibel sounds for a long period of time can cause hearing loss.


It Sounds Like …


• Listening to high-decibel sounds for a long

period of time can cause hearing loss.


It Sounds Like …



Looking at Waves


• People use diagrams to describe sound. Waves consist of curving lines that go up and down as they move away from the sound source.

• Each high point of a wave is called a crest. Each low point of a wave is called a trough.

• The distance from one crest to the next is the wavelength.


Looking at Waves


• Amplitude describes the amount of energy in a wave.

• The volume of a sound and the amplitude of its wave are related.

• Loud sounds, such as jet engines, have large amplitudes. Soft sounds, such as a pin falling on a hard surface, have small amplitudes.


Looking at Waves


• Amplitude is measured by finding the distance from a wave’s highest or lowest point to its midline, or the horizontal line across the middle of a wave.


Looking at Waves



The Travels of Sound


• Sound travels in waves. However, sound can only travel if there are particles that the waves can cause to vibrate.

• Most sounds move through the air. Air and other gases have particles that vibrate as sound energy hits them.

• Liquids and solids are also made of particles, so sound waves can also move through these materials.

14.1 VIDEOS/Science - Transmission of Sound - trimmed 2 wavelength-frequency.mp4




• Sound waves travel through different kinds of matter at different rates.

• The speed at which sound waves pass through solids, liquids, and gases has to do with how their particles are arranged.




• Particles in solids are packed

closely. Particles in gases are far apart. Particles in liquids are in between.

• Sound travels through gases more slowly than it travels through liquids and solids.




• If there are no particles to move, then sound cannot travel.


Sound All Around


• Understanding the properties of sound allows people to control sound.

• Sound insulation contains tiny air cells. Sound is absorbed as the cells trap sound waves, keeping sound inside a room.

• For example, sound engineers place speakers in certain places in movie theaters and performing arts centers so the audience can hear clearly.


Sound All Around


Unit 14 Lesson 1 - WordPress.com · 14.11.2017 · Unit 14 Lesson 1 What Is Sound? Waves of Sound...

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