AQA A2 Physics - Circular Motion Revision Notes

Notes for AQA A2 Physics specification b:physics in context for the Circular Motion part of it. Not the name given in textbook but covers topics such as 'what goes around comes around' etc

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  • Created on: 27-04-11 18:49
Preview of AQA A2 Physics - Circular Motion Revision Notes

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Circular Motion
Round and Round:
Objects moving in a circle with a constant speed must have a force acting on it, directed towards
the centre of the circle. This is called the centripetal force. It is not a specific force, but a name
given to force that causes an object to stay in circular motion. Common examples of centripetal
force are: normal reaction, weight, tension, or components of these forces.
2 2
F = mv
r m r
o F = Centripetal Force
o m = Mass
o v = Constant Linear Velocity
o r = Radius of Circle
o = angular velocity
An object in circular motion is constantly accelerating
o Acceleration is rate of change of velocity
o Velocity is speed in a given direction
o Object is constantly changing direction, therefore constantly accelerating
o Direction is always a tangent to the circle
Angular Velocity ( )
Angular Velocity is the rate of change of angle with time
o Measured in radians
2 radians = 360 degrees
When an object moves at a steady speed along the arc of a circle or radius r travelling a
distance s in a time t
= r
o v = Velocity
o r = Radius
o = angular velocity

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Period and Frequency
The time period (T) of an oscillation is related to the frequency (f) by the equation
o T=1 f
o T is time taken for full circle
Showing the objects steady angular speed can be found from
o T = 2
Back and Forth
On a swing, the centripetal force is provided by the difference between the seat reaction (R) and
the rider's weight (mg)
R - mg = mv
Reaction of the seat on the rider is then given…read more

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The frictional force of the wall must be equal to the
weight of the rider, for the rider to stay in vertical
equilibrium. The reaction of the wall on the rider
provides the centripetal force.
Big Wheel
Although they rotate slowly, a centripetal force is still
required. Throughout the ride, the centripetal force will be
the same value, however the forces that combine to
total this are constantly changing.…read more

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Moment of Inertia
- Resistance to change in angular motion is measure by the moment of inertia about a
chosen axis for the object. A ratio of torque-to-acceleration.…read more

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Rotational Kinetic Energy
There are two types of kinetic energy need to be considered when looking at something in circular
motion: translational and rotational. Translational kinetic energy is the linear energy need to move
an object from point A to B. Rotational energy is the energy used to make an object to rotate.
When a circular object rolls down a slope, both these types of kinetic energy are involved,
therefore the loss of GPE is turned into both types of kinetic energy.…read more

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The Waltzer
o Rotating buckets are mounted on a track attached to an oscillating segmented
o Motion is complex- a combination of vertical SHM, horizontal circular motion and
oscillation of the bucket
o Rider can alter the angular speed through changing the moment of inertia
Moving away from the centre of rotation
Moment of inertia decreases Angular speed decreases
Moving in towards the centre of rotation
Moment of inertia increases Angular speed increases
Swinging ride
o Two cars swing symmetrically in opposite directions
o…read more


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