Copyright © Houghton Mifflin Harcourt Publishing Company What are sound waves? A sound wave is a longitudinal wave that is caused by vibrations and that

Copyright © Houghton Mifflin Harcourt Publishing Company

What are sound waves?

• A sound wave is a longitudinal wave that is caused by vibrations and that travels through a medium.

• In a longitudinal wave, the particles of a medium vibrate in the same direction that the wave travels.

• As the wave passes through a medium, its particles compress together and then spread out.

Unit 2 Lesson 1 Sound Waves and Hearing

How do sound waves travel?

• Sound waves travel in all directions away from their source.

• They can only travel through a medium.

• All matter—solids, liquids, and gases—is composed of particles. The particles in matter make up the medium through which waves can travel.

• In a vacuum there are no particles to vibrate, so no sound can be made.




What determines pitch?


• Pitch is how high or low you think is a sound is. • In a given medium, the higher the frequency of a

wave, the shorter its wavelength and the higher its pitch.

• High-frequency waves have shorter wavelengths and produce high-pitched sounds.

• Low-frequency waves have longer wavelengths and produce low-pitched sounds.

What makes a sound loud?

• Loudness is a measure of how well a sound can be heard.

• The measure of how much energy a sound wave carries is the wave’s intensity, or amplitude.

• The greater the amplitude, the louder the sound.

• The smaller the amplitude, the softer the sound.

• Amplifiers can increase loudness by receiving sound signals and increasing the wave’s amplitude.




How is loudness measured?


• The softest sounds most humans can hear are at a level of 0 dB.

• Sounds that are 120 dB or higher can be painful.

• Rock concerts usually measure about 115 dB.

• Using earplugs to block loud sounds, lowering the volume when using earbuds, and moving away from a loud speaker are all ways to protect yourself from hearing loss.

• Doubling the distance between yourself and a loud sound can reduce the sound’s intensity by as much as one-fourth of what it was.

What is the Doppler effect?

• The Doppler effect is a change in the observed frequency when the sound source, the observer, or both are moving.

• When you and the source of sound are moving closer together, the sound waves are closer together. The sound has a higher frequency and higher pitch.

• When you and the source are moving away from each other, the waves are farther apart. The sound has a lower frequency and lower pitch.




What affects the speed of sound?

• There are two main factors that affect the speed of sound: the type (state) of medium the sound travels through, and the temperature of the medium.

Unit 2 Lesson 2 Interactions of Sound Waves

• Sound travels fastest through solids, slower through liquids, and slowest through gases.

• The more packed together the particles are, the faster the wave will travel.

• The speed of sound depends on the temperature of a medium.

• Sound moves faster at higher temperatures and slower at cooler temperatures.

• Reflection is the bouncing back of a wave when it hits a barrier. Sound waves reflect best off smooth, hard surfaces.


How do sound and matter interact?

• Some matter absorbs sound waves better than other matter.

• A rough wall will absorb sound better than a smooth wall will.

• Soft materials, such as rugs and drapes, will absorb sound better than hard surfaces will.


What is an echo?

• An echo is a reflected sound wave.

• The strength of the echo depends on the reflecting surface.

• Echoes can be reduced using soft materials that absorb the sound waves.

• Echoes can also be reduced using rough surfaces that scatter the sound waves.




How do sound waves interact with each other?• Interference happens when two or more waves

overlap and combine to form one wave.

• In music, beats happen when two sound waves with nearly equal frequencies interfere.



• Echolocation is the use of echoes to find food and other objects.

• Animals produce ultrasound, which are sound waves that have frequencies greater than 20,000 Hz, for echolocation. The frequencies of these ultrasonic waves are too high for humans to hear.

• The time it takes for ultrasound to bounce off an object and return to the animal tells the animal how far away the object is.

Unit 2 Lesson 3 Sound Technology


• Though people cannot send out or hear ultrasound, people can still use echolocation in various technologies.

• Sonar is a system that uses echoes to determine the locations of objects or to communicate.

• Sonar is used to map out ocean floors, find fish, avoid icebergs, and help visually impaired people navigate on land.


How do telephones transmit sound?• All telephones change sound into electrical

signals.

• Cordless phones change the electrical signal into radio waves that travel through air at the speed of light.

• The base picks up the radio waves and changes them back into electrical signals that are sent through wires.

• A computer sends these signals to the other phone, where they are changed back into sound waves.

• Cell phones use radio waves to send signals to phone towers. The towers transfer the signals to phone cables.




How is sound recorded and played back?Information in sound was recorded in the grooves of

records. Now it is stored on CDs or in computer files.

• A compact disc, or CD, is made of hard plastic.

• The information in sound waves is stored by pressing microscopic pits into the plastic.

• The detector changes the pattern into an electrical

signal, which is then changed back into sound waves.



How is sound recorded and played back?

• Sound is also recorded as a digital file in a computer.

• Digital files, such as MP3 files, store large amounts of information.

• More sound files can be stored in a computer or an MP3 player than on a CD.


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Copyright © Houghton Mifflin Harcourt Publishing Company What are sound waves? A sound wave is a longitudinal wave that is caused by vibrations and that