Sound Sound is a type of energy that you can hear. Sounds are made by something vibrating.

Vibrate Vibrate means to quickly move back and forth. Sound changes if an object vibrates faster of slower.

Wavelength is a back and forth motion started by a form of energy. A Sound wave with a high frequency looks like this. A sound wave with a low frequency looks like this.

How Sounds Are Made Objects that move back and forth don’t always make a sound. A sound is only made if the object moves back and forth quickly. When an object vibrates, it makes nearby air molecules vibrate, too.

How a Guitar Makes Sound When a string moves, it pushes nearby air molecules. These push against other air molecules next to them. The string pushes out over and over again. This causes the air molecules to move out in waves. You hear sound when these waves move inside your ears.

Diagram of the ear.

How the individual arts of the ear help you hear. 1. The auricle (outer ear) catches the sound wave. 2. The ear canal produces ear wax, which keeps dirt out of the inner ear. 3. The ear hammer, anvil, and stirrup turn the sound waves into vibrations by “beating” the ear drum, and making it vibrate.

4. Sound enters the inner ear as vibrations. 5. The vibrations travel through the cochlea, which is filled with liquid. 6. As the vibrations move through the cochlea, they send a signal to the brain. 7. The brain understands these signals as sound.

Sound Moves Through Matter An object that vibrates in empty space does not make a sound. Sound cannot move through empty space. Sound only moves through a solid, liquid, or gas. Sound moves fastest through solids. Sound moves slowest through gases.

The Pitch of Sound Pitch is how high or low a sound is. If an object vibrates fast, it makes a high pitch sound. For example, a small bell. If an object vibrates slow, it makes a low pitch sound. For example, a large drum.

Pitch ≠ Volume Pitch is how high or low a sound is. Volume is how loud or soft a sound is. Example: If you ring a small bell strongly, it has a high volume. If you rind a small bell gently, it has a low volume. Important: The high pitch does not change either way you ring the bell.

Musical Instruments…. Musical instruments make sounds in different ways.

Some make sound by air vibrating in a tube. Short tube has a high pitch. Long tube has a low pitch.

Some make sounds by vibrating strings. A short string has a high pitch. A long string has a low pitch. A thin string has a high pitch. A thick string has a low pitch.

Changing Pitch Pitch can be changed by changing how fast an object vibrates. Try This: Stretch a rubber band tightly, pull it, notice how fast it vibrates, and the high pitch. Stretch the rubber band less tightly, pull it, notice it vibrates slower, and the pitch is lower.

Discussion Question A piano has many wire strings of different lengths. The strings make sounds when small hammers hit against them. Describe how a piano can make sounds with different pitches.

Let’s Review You stretch a rubber band and pull on one side. The rubber band makes a sound. Your stretch the rubber band more, and pull on it again. It makes a different sound. What changes about the sound? During a rainstorm, you hear thunder. What causes the sound? Sound will travel fastest through __________. Layla bounces a basketball on a floor made of wood. Why does she hear a sound each time the ball hits the ground? A trumpet can make sounds with different pitches. What happens when the sound changes from a low pitch to a high pitch? Pitch Air moving back and forth Wood The wood makes the air move The air vibrates faster

Let’s Try More… Which of the objects below is translucent? horseshoe magnet; rubber eraser; waxed paper; aluminum soda can 2. The illustration show light that strikes a mirror. Most of the light is __________. 3. Adam rings a bell, and the bell makes a sound. When he touches the bell, the sound stops. Why does the sound stop? 4. Which object is opaque? air; glass; metal; water Waxed paper Reflected The bell stops moving metal

5. Molly listens to a band playing music. She hears many instruments 5. Molly listens to a band playing music. She hears many instruments. The flute makes the sound with the highest pitch. Why is its pitch higher? 6. Which of these shows what happens to a light that strikes a convex lens? a. b. c. d. 5. The air in the flute moves back and forth fastest 6. d

What are some sources of sound in nature? What are some sources of sound made by people?