# AQA P3 EVERYTHING YOU NEED TO KNOW! REVISION NOTES

KEY POINTS YOU NEED TO KNOW FOR AQA P3 EXAM.

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• Created on: 16-04-11 12:08

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P3 REVISION NOTES!
MOMENTS!
The moment of a force F about a pivot is F x d, where d is the perpendicular distance from
the pivot to the line of action of the force.
CENTRE OF MASS!
The centre of mass of an object is the point where its mass may be thought to be
concentrated.
When a suspended object is in equilibrium, its centre of mass is directly beneath the point of
suspension.
The centre of mass of a symmetrical object is along the axis of symmetry.
MOMENTS IN BALANCE
For an object in equilibrium: the sum of the anticlockwise moments about any point is equal
to the sum of the clockwise moments about any point.
STABILITY
The stability of an object is increased by making its base as wide as possible and its centre
of mass as low as possible.
An object will tend to topple over if the line of action of its weight is outside its base.
CIRCULAR MOTION
For an object moving in a circle at constant speed:
The object accelerates continuously towards the centre of the circle
The centripetal force on it increases as:
1. The mass of the object increases.
2. The speed of the object increases
3. The radius of the circle decreases.
GRAVITASTIONAL ATTRACTION
The force of gravity between two objects:
Is an attractive force
Is bigger, the greater the mass of each object,
Is smaller, the greater the distance between the two objects.
PLANETARY ORBITS
To stay in orbit at a particular distance, a small body must move at a particular speed
around a larger body.
The larger an orbit is, the longer the orbiting body takes to go round the orbit.
SATELLITES
The satellite in a geostationary orbit has a period of 24 hours and stays in the same position
directly above the earth's equator.
Geostationary orbits are used for communication satellites.
Monitoring satellites are usually in low polar orbits.
ALL geostationary satellites orbit above the equator.
REFLECTION

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