Have you ever wondered how different sounds are made
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What is sound? - PowerPoint PPT Presentation

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Have you ever wondered how different sounds are made?. What is sound?. Vibration. The back-and-forth motion is called a vibration. What can you notice if you place your fingers against your throat while you talk or hum?

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What is sound?

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Have you ever wondered how different sounds are made?

What is sound?


  • The back-and-forth motion is called a vibration.

  • What can you notice if you place your fingers against your throat while you talk or hum?

    • Vocal cords in your throat vibrate when air moves past them. This allows you to speak.

  • Consider the bell of an alarm clock. When the alarm goes off, the bell vibrates. How does the sound reach your ear?

Sound Waves

  • Think about what happens when an ocean wave rolls under a floating object.

    • In some ways an ocean wave is like a sound wave.

  • A sound wave is a wave that transfers sound through matter and spreads outward in all directions.

Energy Transfer

  • Study this picture. The blue dots show what happens to air particles when the bell rings.

    • Energy from a vibration causes air particles to move.

    • Air particles bump into one another.

    • Some air particles are crowded and some are spaced apart.

    • The air particles move back and forth.

Quick Check

  • Can a sound wave move through water? Explain.

  • When you pluck a string, it vibrates and makes a sound. How can you stop the sound?

You know that sound travels through air. Sound can also travel through solids, liquids, and other gases.

How does sound travel?


  • An echo is a repeated sound that occurs when sound waves bounce off a surface.

  • Dolphins use echoes to navigate and find prey. The sounds they make are reflected by underwater objects, like fish.

The Speed of Sound

  • Sound does not travel at the same speed through all materials.

    • Sound travels:

      • slowest in a gas (air)

      • faster through a liquid (water)

      • fastest through a solid (glass or metal)

  • Sound cannot travel through a vacuum

    • A vacuum does not contain matter.

    • Without matter there can be no sound waves.

The Human Ear

  • What happens when a sound wave reaches your ear?

Quick Check

  • A friend shouts from the far side of an empty gym? You hear the word several times. Why?

  • Why can’t sound travel through outer space?

If all sounds come from vibrations, why don’t they all sound the same?

How does sounds differ?

  • Try tapping your desk and then slapping your desk.

    • Were the sounds the same?

    • Do you think the sound waves you produced were the same?

Wavelength and Frequency

  • The wavelength is the distance from the top of one wave to the top of the next wave.

  • In sound waves, wavelength is the distance from one area of crowded particles to the next.

  • Frequency is the number of vibrations a sound source makes in a given amount of time.

    • When you strike a small bell, it vibrates quickly.

    • The vibrations produce sound waves with a high frequency.


  • The frequency of a sound wave determines its pitch.

  • Pitch is the highness or lowness of a sound.

  • High sounds have high frequencies (beat of a mosquito’s wings)

  • Low sounds have low frequencies (croaks of a toad)

Amplitude and Volume

  • The amount of energy in a sound wave is related to its amplitude.

    • Sound waves with high amplitude are made by objects that vibrate with a lot of energy.

  • Amplitude affects the volume, or loudness, of sound.

    • As an airplane takes off, sound waves with high amplitude fill the air creating a loud sound.

    • When you whisper, your vocal cords vibrate just a little. The sound waves have low amplitude and the volume is low.

Quick Check

  • You tune a guitar. One string makes a sound that is too low. How can you fix this?

  • Why do flutes and tubas make different sounds?

What is sonar?

  • Sonar is a technology that uses sound waves to detect underwater objects.

  • Sonar stands for SOundNavigation And Ranging.

  • It works by sending out sounds and receiving echoes.

Using Echoes

  • A sonar device measures the time difference between the sound and its echo and then makes an image of the object.

  • How do we use sonar?

    • Sailors use it to measure how deep the water is.

    • Fishers use sonar to find schools of fish.

    • Scientists use sonar to map the ocean floor.

    • Others use it to search for shipwrecks.

Quick Check

  • Why might it be important to locate shipwrecks underwater?

  • Why doesn’t sonar work well in air?

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