What is Sound?

Chapter 12Lesson 1

Pages 406-413

Our Goals…

• Explain what makes sound.• Describe how sound varies in pitch

and intensity.• Identify how the intensity of sound is

measured.

Sources of Sound• Vibration- a quick back-and-forth

movement• As things vibrate, the air around it

vibrates… these vibrations move through the air and we hear them as sounds.

• Vibrations can move through gases (air), solids, and liquids.

• Sound waves travel in all directions.• The vibrations that cause sound are

called sound waves.• Sound waves travel in all directions.• Sound waves make parts inside your

ear vibrate and then a signal travels to your brain, and you hear the sound!

Pitch

• Pitch is how high or low a sound is.• Smaller objects usually vibrate faster than

large ones, giving a higher pitch.• Big objects vibrate more slowly,

producing a lower pitch.• Faster vibrating objects produce sound

waves that are closer together… slower vibrating objects produce sound waves that are more spread out.

Intensity

• Intensity is the measure of how loud or soft a sound is.

• Sound waves have a certain amount of energy… a heavier object would have more energy, so it would produce sound waves with more energy… thus, producing a louder sound.

Measuring Sound Intensity

• Sound intensity is measured by using a unit called a bel… named after Alexander Graham Bell.

• For most sounds, the bel is too big a unit to be used, so most sounds are measured in decibels.

• A dB is one-tenth of a bel.

(dB)

100

90

80

70

60

50

40

30

20

10

0 Threshold of hearing

Rustling of leaves

Quiet restaurant

Highway traffic

Jet aircraft at 300 m altitude

Rally Robin!!

• You will mix and then partner up to trade information you learned in this lesson.

• The person with the shortest hair will go first.

Quietly take out your remotes

A quick back-and-forth motion

A. PitchB. VibrationC. DecibelD. Intensity

How high or low a sound is

A. PitchB. VibrationC. DecibelD. Intensity

How loud or soft a sound is

A. PitchB. VibrationC. DecibelD. Intensity

The unit used to measure the loudness of sounds

A. PitchB. VibrationC. DecibelD. Intensity

Vibrations cause sound.

A. TrueB. False

Sound can only travel through air.

A. TrueB. False

Which dog produces a higher pitch?

A.

B.

Which book would have a higher intensity when dropped

on the floor?A.

B.

The bel was named after Thomas Edison.

A. TrueB. False

Sound waves travel in one direction.

A. TrueB. False