Circular motion

The topic of circular motion forms the basis of the orbits of stars, planets and satellites. The concepts allow us to model many physical scenarios from cars on roundabouts or racetracks, to modelling an aeroplane banking during a turn:

  • radian measure of angle and angular velocity

Mathematically students have to understand the relationship between radial and linear motion, and the key to this relationship is the radian measure. This is quite a mathematically simple measure, but students may never have considered in detail the fundamental aspect of an angle measured in radians and what it represents. For them to fully grasp circular motion it is important that they are comfortable with this method of representing angles:

  • application of F = ma = mv2/r = mrω2 to motion in a circle at constant speed

Angular velocity for motion at a constant speed leads on from the understanding of the radian. The idea that acceleration can lead to a change in direction is something that the students will be familar with, but may never have actually had to consider in detail. In this topic, this concept is key. We consider objects moving at a constant speed, but constantly changing velocity, which implies an acceleration. Students have to understand that for circular motion, this acceleration is directed toward the centre of the circle.

Whilst this list provides a source of information and ideas for experimental work, it is important to note that recommendations can date very quickly. Do NOT follow suggestions which conflict with current advice from CLEAPSS or recent safety guides. eLibrary users are responsible for ensuring that any activity, including practical work, which they carry out is consistent with current regulations related to Health and Safety and that they carry an appropriate risk assessment. Further information is provided in our Health and Safety guidance.

Links and Resources

Episode 224: Describing Circular Motion

The whirling bucket of water and the coin on a coat hanger are brilliant demonstrations for getting students to think about the direction of forces involved in circular motion. 

The ideas for developing the concept of centripetal force are useful and there are some excellent ideas for questioning students to check their understanding.

publication year
2000 - 2009

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Episode 225: Quantitative Circular Motion

This set of questions and explanations of the equations required for this topic is very useful and would complement exam questions on the topic.

There are also a couple of experiments designed to confirm the equation. The experimental error on the whirling bung is useful to get the students thinking about how to make reliable measurements.

publication year
2000 - 2009

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