# circular motion

## angles can be expressed as radians

the angle in radians is defined as the arc length/radius of the circle

for a complete circle the arc length is just the circumference of the circle

half a circle is worth pi r, 1/4 is worth 1/2 pi r etc

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## angular displacement and angular speed

Angular displacement is given by the equation 2pi t/T where T is the time for 1 rotation

Angular speed is defined as the angular displacement per second

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## centripetal acceleration

The acceleration towards the centre of the circle is known as the centripetal acceleration. For an object moving at a constant speed v in a circle of radius r it can be shown that a=v2/r. Centripetal means towards the centre of the circle.

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## centripetal force

Centrifugal force does not exist

Centripetal force always acts towards the inside of a circle

The centripetal force may be one of many things such as tension in a string, gravity, or an electric or magnetic field

The relationship between velocity and the centripetal force is F=(mv2)/r

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