4.2 Sound

Sound 4.2

• Sound is produced when something vibrates. When something vibrates, it passes the vibration to the surrounding environment such as air.
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Compressions and Rarefractions

• The vibrations create regions of space in which the air particles that are bunched together are called Compressions, and regions where they are more spread out are called refractions.
• Sound waves are alternating movements of compressions are rare fractions.
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Sound Waves

• A wave carries energy from one point to another.
• In a Transverse Wave, particles move at right angles to the direction of movement of the waves.
• Particles move back and fourth in the same direction, but don't move along the wave. They just pass the energy down the wave. This is called a Longitudinal Wave.
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How Fast would Sound Travel?

• The more closely the particles are packed in the medium, the faster sound will travel. This is because the sound does not have to move to bump into other particles.
• For example a sound will travel faster in a solid than a liquid or a gas because particles would have to run around looking for other particles in a gas as they are spread further apart than a solid or liquid.
• Solid (Fastest) Liquid (Medium) Gas (Slow)
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The Temperature of the Air and Hard and Soft Surfaces

• Sounds travel faster in warmer air than in cooler air because the articles in warmer air move with greater kinetic energy.
• Hard surfaces, such as a tiled bathroom, reflects sounds and makes an echo.
• Soft surfaces such as cushions and carpets and curtains absorb sound and convert to the energy to heat. Soft surfaces are used in cinemas and music halls to make sure no other noises interfere with the main sound.

Can Sound be Measured?

• the time difference between sending and receiving a sound can be measure using sonar (solar navigation and ranging) and this can also be used to measure the depth of objects in the sea.
• Different sounds can be compared by analysing the sounds using a cathode ray oscilloscope (CRO).
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• Caption: To find the distance of somethinf deep in the sea, use the sonar to caculate the time it takes to reach to the object and then return. Divide the time by 2, then multiply the answer by 1500.

Frequency and Pitch

• -A source that vibrates rapidly produces a sound of higher pitch/frequency.
• -The number of vibrations a sound makes each second is called the frequency of a wave. Frequency is measured in hertz (Hz).
• -The wave length of a sound is the distance between wave peaks, also know as successive peaks.
• -Loud sounds (Taller waves)
• -Quiet Sounds (Shorter waves)
• -High Frequency (Short wave length)
• -Low Frequency (Long wave length)

Frequency Pictures

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• Caption: The areas with more dots are called the compressions. The areas where there is a lot os space between each particle is know as the rarefaction.

Out of our Hearing Range

• Ultrasound is the term used for frequencies outside of our hearing range.
• Frequencies lower than our hearing range are called infrasound.
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• Caption: This is how Ultrasounds work to analyse a baby in a stomach