# Physics Unit 3-Topic 1

Overview of topic 1 for Unit 3 physics- forces

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• Created by: Susie
• Created on: 02-04-12 13:35

## Moments

Moments

The turning effect of a force is called the moment.

The size of the moment is calculated using the following formula:

moment (Nm)=force (N) x perpendicular distance (m)

To increase the size of the moment we can: increase the force applied or increase the perpendicular distance between the line of action and the pivot.

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## Centre of Mass

The Centre of Mass

The Centre of Mass of an object is the point at which an object balances.

When an object is suspended from a single point, the C.o.M can be found directly below this point.

(when an object is in this position it does not exert any turning force because the C.o.M is directly below the pivot)

We can then hang the object from a different point and the C.o.M is found where the two lines meet.

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## The Law of Moments

The Law of Moments

The Law of Moments is very simple:

Total clockwise moments=Total anticlockwise moments

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## Centripetal Force

Gravity and our Solar System

The bigger the mass of an object...the bigger the force of gravity

• The orbit of any planet is known as an ellipse
• The sun is at one focus

As the distance beween two bodies increases, the force of gravity between the two decreases proportionally.

Tip:take the number of increase e.g. x4, square it (16) and then divide it by 1

= 1/16

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## Artificial Satellites

Communications Satellites: link up different countries so that TV, radio and telephone calls can be shared.

A geostationary communtications satellite has a geostationary orbit-> this means that the satellite take the same amount of time for an orbit as the earth does (i.e. 24 hours) and travels at this speed. This means that it is constantly above exactly the same point on the equator.

Monitoring Satellites: collect information about the atmosphere.

A Polar Monitoring Satellite has a low Polar orbit-> this means that it continously passes over both the North and South Poles and the Earth spins beneath it

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