GCSE Physics Unit 3 - Waves, moments and stars

Notes covering;

  • transverse and logitudinal waves
  • ultrasound
  • sound waves
  • moments
  • centre of gravity and centre of mass
  • stability
  • birth, life and death of stars

Created for the AQA 2011 unit 3 exam - any changes to the specification since then are not included.

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  • Created by: Sarah
  • Created on: 03-01-12 18:41
Preview of GCSE Physics Unit 3 - Waves, moments and stars

First 47 words of the document:

Longitudinal waves have particles vibrating along the direction of travel of the wave,
e.g. sound waves.
Transverse waves have particles vibrating at right angles to the direction of travel of
the wave, e.g. light waves.

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Page 2

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If you ring an electric bell in a sealed bell jar, you will hear a ring. But when a vacuum
pump attached to the jar there is no sound because there are no particles for the sound
to pass through.
How does a loudspeaker work?
The cone of the loudspeaker vibrates.
The air next to the cone vibrates also.
Each particle passes on the vibrations.
Compressions and rarefactions are caused.…read more

Page 3

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Reflecting Sound
Refractions of Sound
"Sound travels better over the water at night"
During the day the temperature is constant.
Sound travels in straight lines.
At night the sea retains heat, so the air above the water is warmer.
The amount of refraction depends on the temperature of the air.
Sound travels in a curved path.
Sound is `focused' on the other side of the lake, so it sounds louder.
Ultrasonic Waves
Ultrasonic waves are partially reflected whenever they meet a boundary.…read more

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Checking unborn babies
The mother's stomach is covered in gel
A transmitter sends out ultrasonic pulses
Different parts reflect the pulses differently
Receiver picks up echoes and reflections
Computer screen displays image of the foetus
Xrays cannot be used as they might hurt the foetus.
3) Cleaning
Dentists vibrate plaque from teeth
Jewellery can be placed in an ultrasonic bath where dirt is shaken by ultrasonic
pulses to clean delicate mechanisms without taking them apart.…read more

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To increase the moment created with a spanner, we can
a) Increase the length of the spanner's handle
b) Increase the force exerted on the spanner
The Principle of Moments
Think of a seesaw. When both sides are balanced, the seesaw is stationary
the sum of the total clockwise moments is equal to the sum of total anticlockwise
moments. From here we can calculate weights or moments
E.g. Julie, weighing 400N, is sat on a seesaw 0.4m right from the centre.…read more

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We can decrease the chance of a body toppling by
Lowering the Centre of Gravity
Increasing the width of the base of the body
Why would the crane be unstable without the counterbalance?
The load would cause a moment, pulling the crane around and toppling it.…read more

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The Death of a Star a Star the size of the Sun…read more

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The atoms are forced together so strongly by the gravity that the WHITE DWARF is
very densely packed.
The Death of Stars Massive Stars
The death of a bigger star is different to that of our Sun.
If enough matter is left behind, it may be so dense and have such a strong
gravitational field that no light or electromagnetic radiation can escape it ­ a
BLACK HOLE.…read more


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