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Sound

Sound. What is sound?. Any object vibrating in air creates sound waves by moving air molecules back and forth. Sound waves are longitudinal and are composed of compressions and rarefactions. Speakers. An alternating current is supplied to the coil.

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Sound

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  1. Sound

  2. What is sound? • Any object vibrating in air creates sound waves by moving air molecules back and forth. • Sound waves are longitudinal and are composed of compressions and rarefactions.

  3. Speakers • An alternating current is supplied to the coil. • This induces an alternating magnetic field which causes a force on the magnet. • The moving magnet causes the cone to vibrate and make sound.

  4. Speakers • If we increase the frequency of the alternating current, we increase the frequency of the sound.

  5. Properties of Sound • Sound waves travel through solids, liquids and gases. They cannot travel in a vacuum. • Sound waves travel faster through solids because the molecules are closer together.

  6. Echoes • A sound echo occurs when a sound wave is reflected off of a hard, smooth surface. • To prevent echoes you can cover walls with a soft material that is uneven (like in music studios).

  7. Summary • Sound waves are produced when a vibrating surface pushes and pulls on the surrounding substance. • Sound waves are longitudinal with alternating compressions and rarefactions. • Sound travels through solids, liquids and gases but not vacuums. • An echo is due to sound reflecting off of a smooth, hard surface.

  8. Speed of Sound

  9. Speed of Sound • The speed of sound depends on the substance it is traveling through. • In general, sound travels faster in solids and liquids.

  10. Speed of Sound • The speed of sound in air is approximately 340 m/s. • The speed of sound in water is approximately 1400 m/s.

  11. Example 1 • A person is standing in front of a large wall. They clap their hands and hear an echo 2 seconds later. How far away is the wall?

  12. Example 2 • Dolphins use echo-location to find fish. A dolphin sends a sound wave and hears the echo 1.3 seconds later. How far away is the fish?

  13. Summary • The speed of sounds depends on the substance and the temperature of the substance. • The speed of sound in air is about 340 m/s. • The speed of sound in water is about 1400 m/s.

  14. Musical Sounds

  15. Musical Sounds • Musical notes are sound waves that change smoothly and have a pattern that repeats. • Noise is sound waves that change randomly without any pattern.

  16. Instruments • Musical instruments, including your voice, create sound waves by vibrating air. • At certain frequencies, the vibrations become stronger. The instrument resonates at these frequencies.

  17. Waveforms • Sound waves are longitudinal but can be converted into transverse waveforms.

  18. Waveforms • The loudness of a sound changes the amplitude of the waveform. A large amplitude means a loud sound. • The pitch

  19. Summary • Instruments produce sound by vibrating the air around it. • The loudness of a note increases the amplitude of the wave. • The pitch of the note increases the frequency.

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