Sound waves

Part 1 of 9Sound and vibration

• Vibrate to move backwards and forwards very quickly
• Sourcethings that vibrate make sounds
• Drumhitting a drum makes it vibrate, and hitting it harder makes it vibrate more and sound louder
• Voicevibrations of the vocal cords make the sound when you speak
• Loudspeakerits paper cone vibrates, which small objects placed on the cone show by bouncing

Part 2 of 9Loudness and pitch

• Variationsounds differ in loudness and pitch
• Pitchthunder has a low pitch and a crying baby has a high pitch
• Loudnessa bigger vibration gives a louder sound
• Guitarplucking the string with more force makes a louder sound

Part 3 of 9How 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.

Part 4 of 9Particle movement in a sound wave

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

Part 5 of 9Effects of sound vibrations

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

Part 6 of 9Media for sound

• Medium the substance a sound wave moves through
• Solids, liquids and gasesall can be a medium because they contain particles
• Gassound travels through air
• Solidsound travels easily through a table when an ear is placed on it
• Liquidsound travels through water, which whales and dolphins use to communicate
• Same wayin all three states the wave makes particles vibrate backwards and forwards

Part 7 of 9No sound in a vacuum

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

Part 8 of 9Modelling 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.

Part 9 of 9String telephone investigation

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