Physics of Sound: What are the properties of sound?

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What is sound? It is a form of energy that travels in waves, like the ocean, from an object to an ear. When something vibrates, it sends out waves in the air. Objects can be identified by the kind of sound they make. The object making the sound is called the sound source, and your ear is a sound receiver. How can your ear tell sounds apart? The ability to identify sounds and tell sounds apart is called sound discrimination.

If we could see sound, this is what it would look like.

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How do we use sounds every day?

  • To give each other information.

  • To send warnings to each other. Sound travels long distances quickly even when we cannot see (like in the dark). In fact, sound moves at 340 meters per second (which is faster than an airplane) and is almost one lap around the track.

  • To communicate a need. For example, babies cry when they need something.

Other animals use sound every day to communicate with each other too.

  • For example, monkeys make different sounds for different predators. (One sound for snake, other sounds for leopard, eagle, etc.)

  • Baby animals make sounds to tell the mother they are hungry (kittens meowing).

What are properties of sounds? Examples include: Loud, soft, high, low, scratchy, and ringing.

What can a sound tell you about the object that made it? For example, what are the properties of objects that make a loud sound, compared to objects that make a soft sound?

Sound travels from an object to an ear in waves, like ocean waves. When sound waves reach your ear, the little bones in there vibrate (shake).

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How an object feels, looks, tastes, smells, or sound is a property of that object. The loudness of sound is the volume (like raising the volume on the TV to make it louder) and pitch is how high it is. Longer objects make lowers pitched sounds, and shorter objects make higher pitched sounds (like a mosquito). High pitch is the same thing as high frequency, because the object is vibrating more frequently (faster).

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Communication tools that use sound

  • Voice

  • Musical instruments

  • Animal sounds

  • Sonar (a device that sends waves through water to measure or find something)

  • Morse Code: code for letters and animals using sound

Investigations

In the drop challenge, we drop objects without looking, to describe the sound they make, and compare sounds. Then, we describe how we discriminated between sounds, and discuss sound properties. We then create a drop code. A code is a set of symbols representing letters, numbers, or other information used to communicate.

Playing with tuning forks, we discover that vibrations cause sound.

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Playing with instruments, we look at how shorter objects make higher pitch sounds, because they vibrate more frequently (faster). The shorter metal (the blue below) makes a higher pitch sound, and the longer one (the red), makes a lower pitch sound.

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Another thing that affects pitch is tension. The more tense (tight) is the string, the higher frequency sound it makes. With more tension, vibrations are faster and the pitch is higher.

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We experiment with how sound travels through air, liquids, and solids. We learn that sounds travels slowest in air, faster in liquid, and fastest in solids.

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Resources

1. Multilingual Monkeys: Video on monkey alarm sounds for predators

2.Video: Science of Sound

3. Powerpoint presentation on sound

4. Activities on sound for home

5. Physics of Sound Unit Summary

6. Monkey language

Practice at Home

1. How did you use sound today?

2. Strum a real or a homemade guitar (you can tie two pieces of fishing line or string tightly to something). What do you hear? What do you see happening to the string? (Remember, vibrations cause sound)

3. Fill up two glass bottles with different volumes of water. Draw the bottles. Blow in them. Which makes a higher pitch sound (the one with less air, or the one with more air)? (In this activity, what is the sound source (from where the sound is coming) and what is the sound receiver (to where the sound is going)?