Circular Motion
The study of circular motion at GCSE provides some conceptual challenges for students. Even though they do not usually have to engage with the mathematical treatment of this until A level, there are some potential counter intuitive ideas that arise which can cause problems at GCSE. The most common are listed below.
1) When objects move in a circular path they are accelerating even though they are travelling at constant speed. Students often think this because they have learnt or assume that acceleration only means speeding up or slowing down and the fact that a change in direction is also an indicator of acceleration is overlooked or played down.
2) When an object is moving in a circular path there is a force towards the centre of the circular path. Experiences on roundabouts, fairground rides and the widespread incorrect use of the term centrifugal force as an outwards one help to reinforce some alternative ideas.
3) If the force causing an object to move in a circular path is removed, it will travel off in a straight line as long as not other forces act upon it. The belief that an object will curve or spiral off, even when no forces are acting upon it is widespread.
The first of this is perhaps most challenging to address in class as it stems from a potentially incorrect definition or understanding of acceleration and so a revisiting of what acceleration is may be the best way to explore this. The first resources here, a video that could be reproduced in a class if you had a bowling ball and hammer, helps to try and address 2) and 3) above.
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, SSERC 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
Circular Motion and Bowling Balls
This simple video with a bowling ball and rubber mallet shows a ball moving at roughly constant speed but as a force is applied (it is hit with the hammer) it changes direction but not speed.
The force can be seen to be acting towards the centre of the circular path and this causes the ball to accelerate (change direction) but not speed up or slow down.
Also, when the force is removed, you can see how the ball travels off in a straight line. You can easily reproduce this demo in class if you have a bowling ball and mallet.
Episode 224: Describing Circular Motion
This resource from the institute of physics was written to introduce AS physics students to circular motion so it sits nicely in the GCSE triple science framework, extending the previous work on forces. It describes a lovely series of demonstrations – you really must try for yourself the one with the jelly - which should get your students thinking and developing their own ideas.
Although most will already know about whirling a bucket of water around without the water falling out, it still has to be done! The table at the bottom of page 2 would make a useful cut and stick activity where students have to match the force to the example. Teachers will appreciate the practical tips and the background notes on the physics involved.
Although it's not listed here, a sparkler in a drill also makes for a lovely demonstration. Secure a sparkler firmly in the bit of a drill. Preferably use a cordless drill because you're going to want to do this outside. Bend the base of the sparkler (the part near the drill) over at 90 degrees. Then set light to the sparkler and start the drill. Students will see the circular trail left by the sparkler, but also be able to observe that the sparks fly off in straight lines. Very pretty physics!
Playing with Toys in Space *suitable for home teaching*
This film is really short but it’s super! It would make an excellent introduction to circular motion as there is effectively no gravity. Challenge your students to explain the motion of the car and then ask them again at the end of the topic to assess the progress they’ve made. Of course the centripetal force comes from the track rather than the car as suggested by the notes. The other half of the force pair is the force from the car on the track.
Flying Weightless *suitable for home teaching*
This article, written for GCSE level students, provides a good example of circular motion in action for “reading around the subject” and as such it would be useful to read as part of a piece of homework. Consider asking students to explain the article to an adult family member when they have read it. The adult then signs the homework diary to confirm that they have discussed the article with the student. The discussion will be worthwhile for all concerned and doesn’t require any marking.
Ladybird in Circular Motion
You’ll be amazed at what this ladybird (English for ladybug) can do. You’ll love the way she goes round in circles just to show you her velocity and acceleration and you’ll hardly be able to wait to show her off to your students! Engaging and fun, this simulation nevertheless contains all the right physics,You could start by selecting comparing linear motion with circular motion. Once you start with circular motion, try removing the vector labels for velocity and acceleration and asking your students to predict what they should look like.
Nuffield Physics: Questions Book V
Published in 1967 (!) this resource is not recommended for students but teachers will find that chapter one is packed full of great ideas for demonstrations, practical work and questions about circular motion. Two or three of these demonstrations would serve as a good introduction to the topic and teachers will appreciate the plethora of questions given as they can be used effectively with the students to really get them thinking. The bucket of water is a must of course and, although you may find it difficult to get hold of a record turntable these days, many physics departments will already have alternative turntables.
