Circular motion at GCSE provides some conceptual challenges for students; the most common alternative conceptions are listed below, along with a few resources to support student's learning.
- When objects move in a circular path they are ‘not’ accelerating because 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 acceleration is overlooked.
- When an object is moving in a circular path there is a force ‘away from’ the centre of the circular path. Experiences on roundabouts, fairground rides and the widespread use of the term centrifugal force help to reinforce this way of looking at things, but this is in contradiction to the fact that a force towards the centre is what is required to keep going around in a circle.
- If the force causing an object to move in a circular path is completely removed, the object will leave along a ‘radius or spiral off’ the circular path. Whereas in fact it will move off the circular path along a tangent.
Here are some ideas and resources for teaching this area of the curriculum.
Practical activities
From the Institute of Physics, Describing Circular Motion introduces students to the importance of circular motion and the need for a centripetal force to keep an object moving along a circular path. The activities include: observing circular motion, whirling bucket and centripetal force, discussing examples of centripetal forces, further demonstrations of centripetal force.
Videos
The two cartoon characters in Why Doesn't the Moon Fall Down? clearly and convincingly explain Newton’s reasoning behind the circular motion of the Moon. Show it to your students if they are unsure about how satellites like the Moon orbit the earth.
The YouTube video Circular Motion and Bowling Balls demonstrates a bowling ball moving in a straight line then a centripetal force is applied using a hammer resulting in circular motion. A very clear demonstration in a real world situation that allows students to understand where forces are applied to provide circular motion.
Website
The Astro Academy: Principia website provides resources including orbital experiments conducted by astronaut Tim Peake aboard the International Space Station; dynamic analyses of the results; ground-based analogue experiment guides for students and teachers; and a suite of further space science and education guides.
Further support for physics teaching ideas and practicals
Teaching practical science: physics
Effective GCSE practical work: Physics