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What is sound?

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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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Presentation Transcript
  • 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
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
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
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?
  • 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
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
The Human Ear
  • What happens when a sound wave reaches your ear?
quick check1
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?
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
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
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 check2
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
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
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 check3
Quick Check
  • Why might it be important to locate shipwrecks underwater?
  • Why doesn’t sonar work well in air?