P3 Revision Notes:Moments

Notes on P3 AQA Moments

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• Created on: 26-03-12 17:45

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REVISION NOTES: PHYSICS 3
UNIT 1: MOMENTS
Turning Effects
Trying to unscrew a nut requires a spanner. It is common knowledge that a longer spanner makes it
easier ­ this is because less force is required to pull the nut out. Unscrewing a nut is an example of a
turning effect. The turning effect of the force is called the moment, which can be increased by:
increasing the size of the force
using a longer instrument
You can work out the moment using this equation:
Levers
The diagram below shows a crowbar being used to lift a safe.
Imagine that someone is pushing down on that crowbar, and that is what causes the push. The push
is the force applied by a person, whom we call effort, when trying to lift objects ­ the load around
a pivot (the point at which the crowbar turns).
Centre of Mass
We say that there is a point of an object where we can think of it as though the weight acts at that
single point. We call this the centre of mass or centre of gravity. The centre of mass is the point
of an object where its mass may be concentrated.

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REVISION NOTES: PHYSICS 3
UNIT 1: MOMENTS
A hanging object rests with its centre of mass directly below the point of suspension. This means that
the object is said to be in equilibrium. Because the centre of mass is directly below the point of
suspension, no turning effect is exerted by the weight, as shown with the left hanging flower basket.
When an object is moved from its original position and released, it will swing back into its
equilibrium position.…read more

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REVISION NOTES: PHYSICS 3
UNIT 1: MOMENTS
Stability
Objects have a certain amount of stability, where they can withstand a certain amount of tilting
before they topple over.…read more

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REVISION NOTES: PHYSICS 3
UNIT 1: MOMENTS
Circular Motion
An object attached to a piece of string, or similar material, when whirled round, will move in a
circular direction in the air. A good example of this is the hammer throw. The arrows on the image
below show this example of circular motion:
Therefore, the object is constantly accelerating towards the centre of the circle. So the force on the
object acts towards the centre of the circle.…read more

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REVISION NOTES: PHYSICS 3
UNIT 1: MOMENTS
Gravitational Forces
Any two objects exert a gravitational force on each other.…read more

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REVISION NOTES: PHYSICS 3
UNIT 1: MOMENTS
Planetary Orbiting
The Moon orbits the Earth in a circular orbit, and the Earth, along with the other planets, orbits the
Sun in a slightly squashed circle ­ an elliptical orbit. In each case, an object orbits an object far
larger than itself ­ and the centripetal force is present because of the gravitational forces of
attraction between the smaller object and the larger object.…read more

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REVISION NOTES: PHYSICS 3
UNIT 1: MOMENTS
environmental observations. These are much lower orbits ­ purely so that we can see as
much detail of the Earth as possible.…read more

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