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2.1Unit 6: Sound, the Earth and eclipses

Sound waves

5 min read 11 parts Lesson 1 of 5 1 quiz

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Lesson summary

2.1 Sound waves — CHECKPOINT EARTH AND SPACE 0893 notes: Explain that sound comes from vibrations, travels as a wave through particles and cannot travel through a vacuum.Vibrate = to move backwards and forwards very quicklySource — things that vibrate make soundsDrum — hitting a …

  • Loudspeaker
  • Wave direction
  • Very loud sounds
  • Very quiet sounds
  • Solids, liquids and gases
  • Tight string

Section 1 of 11Sound and vibration

  • Vibrate = to move backwards and forwards very quickly
  • Source
    • things that vibrate make sounds
  • Drum
    • hitting a drum makes it vibrate, and hitting it harder makes it vibrate more and sound louder
  • Voice
    • vibrations of the vocal cords make the sound when you speak
  • Loudspeaker
    • its paper cone vibrates, which small objects placed on the cone show by bouncing

Section 2 of 11Loudness and pitch

  • Variation
    • sounds differ in loudness and pitch
  • Pitch
    • thunder has a low pitch and a crying baby has a high pitch
  • Loudness
    • a bigger vibration gives a louder sound
  • Guitar
    • plucking the string with more force makes a louder sound

Section 3 of 11How a sound wave travels

  1. A vibrating object moves forwards and pushes the air particles in front of it.
  2. Those air particles vibrate backwards and forwards in time with the object.
  3. They make the particles in front of them vibrate.
  4. The vibration passes from particle to particle as a sound wave.
  5. The wave reaches the ear and the ear detects the vibration.

Section 4 of 11Particle movement in a sound wave

  • Particles
    • they vibrate backwards and forwards along the direction in which the wave travels
  • Wave direction
    • the wave moves away from the source, but the particles do not travel with it
  • Speed
    • sound travels through air at about 343 metres per second
  • Energy
    • sound waves transfer sound energy, and the vibration passes to other objects, which then vibrate

Section 5 of 11Effects of sound vibrations

  • Very loud sounds
    • their vibrations can damage the ears
  • Very quiet sounds
    • their vibrations may be too small for the ears to detect
  • Pitch
    • a sound at a certain pitch can cause damaging vibrations even when it is not very loud
  • Objects
    • vibrations from a high-pitched sound can break glass

Section 6 of 11Media for sound

  • Medium = the substance a sound wave moves through
  • Solids, liquids and gases
    • all can be a medium because they contain particles
  • Gas
    • sound travels through air
  • Solid
    • sound travels easily through a table when an ear is placed on it
  • Liquid
    • sound travels through water, which whales and dolphins use to communicate
  • Same way
    • in all three states the wave makes particles vibrate backwards and forwards

Section 7 of 11No sound in a vacuum

  • Needs
    • to hear a sound there must be a vibration and a medium with particles
  • Vacuum
    • a space with no particles, so there is nothing to vibrate and no sound wave can travel
  • Space
    • space is a vacuum, so sound cannot travel through it and the Sun could not be heard
  • Bell jar
    • an electric bell in a jar can be seen vibrating, but its sound cannot be heard once the air is pumped out

Section 8 of 11Modelling a sound wave with a spring

  1. Stretch a slinky spring across a smooth flat surface.
  2. Mark positions on the spring with chalk or pieces of paper to represent particles.
  3. One person holds one end still.
  4. Another person moves the other end backwards and forwards.
  5. Observe that the wave travels along the spring while each mark only moves backwards and forwards.

Section 9 of 11String telephone investigation

  • Set-up
    • two cups joined by a long string, with one person speaking quietly into one cup and another listening at the other
  • Tight string
    • the voice is heard because the sound wave passes through the string
  • Slack string
    • the sound is not heard or is much weaker
  • Gripped string
    • gripping the string stops the vibrations, whatever position it is gripped at
  • Conclusion
    • sound needs vibrations passing through a medium to travel
  • Fair test
    • speak with the same loudness each time, for example by using a recording

Section 10 of 11More from the specification

  • Compression
    • A region in a longitudinal sound wave where particles are crowded together, corresponding to higher local pressure and density.
  • Rarefaction
    • A region in a longitudinal sound wave where particles are spread furthest apart, corresponding to lower local pressure and density.
  • Oscillation
    • The repetitive back-and-forth vibrating movement of particles about a mean resting position.
  • Frequency and Pitch
    • Frequency is the number of complete vibrations per second in hertz (Hz); higher frequencies produce higher pitched sounds.
  • Amplitude and Loudness
    • Amplitude is the maximum displacement of particles from equilibrium; waves with greater amplitude carry more energy and sound louder.

Section 11 of 11More from the specification

  • Production of sound by vibrations
    • Sound is produced whenever an object vibrates rapidly back and forth.
      • (such as vibrating drum skins or guitar strings)
  • Longitudinal wave nature
    • Sound travels as a longitudinal mechanical wave where medium particles oscillate parallel to the direction of wave propagation.
  • Frequency and pitch
    • High-frequency vibrations produce high-pitched sounds, whereas low-frequency vibrations generate low-pitched sounds.
  • Need for a material medium
    • Sound waves require particles to transmit vibrations and therefore cannot propagate through a vacuum.
  • Group
    • A column of the Periodic Table.

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