Sound Waves (from ReadWorks)

Both of these sounds travel through air. How are they different?

​Sound Waves

(from ReadWorks)​

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​This text is adapted from an original work of the Core Knowledge Foundation, and taken from the ReadWorks site.

Light and sound can both travel through mediums. A medium is a substance that light or sound can travel through, like a solid, a liquid, or a gas. However, there is a difference. Sound must have a medium to travel through—a solid, liquid, or gas. Light, on the other hand, does not need a medium. Light can travel through the emptiness, or vacuum, of outer space. Sound cannot.

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​The speed at which light and sound travel is also different. Light travels much faster than sound. There are important ways that light and sound are similar. They are both forms of energy that travel in waves. There are also other similarities.

​Light waves can be different lengths. Some are long and some are short. It is the length of a light wave that makes it appear to be a particular color.

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Perhaps you are wondering whether sound waves differ from one another. Imagine these two sounds—a baby crying for its mother and an adult yelling. Both of these are sounds. The sound waves of each travel through the same medium, air, so they are alike in that way. But a baby crying surely sounds different than an adult yelling! The baby makes a high-pitched, “screeching” sound. When an adult yells, it is a low- pitched, deep tone. Could this difference in pitch, or how high or how low a sound is, come from different kinds of sound waves?

​The answer is yes and it has to do with the length of the sound waves! It helps if we first understand how vibrations affect sound waves. Faster vibrations produce shorter sound waves, which make sounds with a higher pitch. The baby’s screeching sound vibrates very rapidly, making shorter, but more, sound waves. Can you think of some other sounds that have a high pitch? Slower vibrations produce longer waves, which make sounds with a lower pitch. A yelling voice makes longer, fewer waves so you hear a lower pitch. Pitch describes the highness or lowness of a sound. Can you think of some sounds that have a low pitch? Try changing your voice pitch. Can you speak in a high, squeaky voice? Can you speak in a low, rumbling voice?

Which sounds are high-pitched?

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Which are low-pitched?​

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Multiple Choice

Choose the sound that has a high pitch.

Multiple Choice

Choose the sound that has a low pitch.

Multiple Choice

Sound and light are both forms of energy that travel in what?

• A. waves

• B. a vacuum

• C. a gas

• D. pitch

Multiple Choice

Describe how vibrations affect the length of sound waves.

• A. Faster vibrations produce longer sound waves.

• B. The boats make vibrations in the water and it makes the waves bigger.

• C. Slower vibrations produce shorter sound waves.

• D. Faster vibrations produce shorter sound waves.

Multiple Choice

How does the length of a sound wave affect the way it sounds? Support your answer with details from the text.

• A. The length of a sound wave makes waves in the air. I know this because it was written in the passage that sound needs a medium to travel through.

• B. The length of a sound wave makes a sound have a higher or lower pitch. I know this because it was written in the passage that shorter sound waves have a higher pitch.

• C. Longer sound waves have a higher pitch. I know this because it was written in the passage that pitch describes the highness or lowness of a sound.

• D. The length of a sound wave affects how long you say hi while waving to your friend. I know this because I tried it.

Multiple Choice

What is the main idea of this text?

• A. Waves at the beach are caused by the wind.

• B. Sound can have a low or a high pitch.

• C. Sound travels in waves like light, and those waves determine the pitch of the sound.

• D. Sound needs a medium to travel through.