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

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Page 1

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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.

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…

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.…

Page 4

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2) 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…

Page 5

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13.1 Moments

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…

Page 6

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Centre of Gravity and Centre of Mass

We can use the fact above to find the centre of mass of a body.

1. Cut out an irregularly shaped piece of card.
2. Make several holes around the edge.
3. Using a clamp stand and pin, suspend the object so it…

Page 7

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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…

Page 8

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Use the Principle of Moments.

The Birth of Stars

Stars are formed when large clouds of dust and gas in space are pulled
together by gravitational attractive forces. Once the star begins forming, the large
mass of the star may attract smaller masses which begin orbiting the star such as…

Page 9

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The Death of a Star a Star the size of the Sun

Page 10

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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…


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