# Unit 3

AQA GCSE Physics unit 3

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### Page 2

Moments
A moment is the turning effect of a force around a pivot (or axis of rotation).

moment = force × perpendicular distance from the line of action of the force to the
pivot
(newton metre, Nm) (newton, N) (metre, m)
The load is the object you are trying to…

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Centre of mass
The centre of mass of an object is the point at which all of the mass of the object is said to be
concentrated.

To find the centre of mass for a regular shape you simply draw on the lines of symmetry of the
shape and where…

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Circular motion
An object will remain at a constant speed/not move if there is no resultant force acting on it.
However when something is moving in a circle there is a resultant force acting on it that
makes the object move in a circle ­ this resultant force is called…

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Gravity and planetary orbits
Any two objects are attracted to each other by gravity ­ they exert a gravitational force on
each other Isaac Newton discovered gravity, and he said that the force of gravity between
any two objects:
is an attractive force
gets bigger with the mass of each…

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gravitational attraction is stronger, and the planet has a smaller orbit, travels faster and takes
less time to complete an orbit.
The stronger the gravity the faster the circular motion.
The size of the force quickly decreases as the distance away from the sun increases. If you
double your distance…

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A satellite is just something which is lower in mass that orbits something higher in mass e.g.
the moon is a satellite of the earth, or the earth is a satellite of the sun.

There are four main purposes of satellites:
­ Monitoring the Earth e.g. weather/climate (Low polar orbit)…

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This type of satellite is ideal for collecting information
for weather prediction or surveillance (spying) because
1. It sees the whole surface of the planet each day.
2. It is close enough to the Earth to get detailed and reliable information

Geostationary satellites are too high to take good weather…

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compressions, which then pass them on again. They're known as longitudinal waves. This is
how sound waves travel along through solids, liquids and gases.

Longitudinal wave oscillate/vibrate parallel (in the same direction) to the direction of travel e.g
sound wave.
A vibrating object sends out sound waves through the air…

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A microphone connected to an oscilloscope can be used to show the waveform of a sound. It
converts sound waves into electrical waves which show up on the cathode ray oscilloscope.
To study sound need a signal generator, CRO and loudspeaker.

Amplitude ­ Is the height of the wave
The…

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