Momentum
It has been suggested by some that the concept of momentum is more intuitive and accessible for students to grasp than acceleration and some courses have been designed to introduce momentum before acceleration. When studying motion it is common for students to muddle and merge speed, velocity and acceleration into ‘movement’ and not adequately differentiate between them. The view of the ‘momentum first’ teaching approach is partly that that momentum is more accessible as a measurement of ‘movementness’ rather than the rate of change of a rate of change (i.e. acceleration). Either way, there is a message here for teachers about making sure we are clear and separate these overlapping ideas otherwise the students will struggle.
The two key ideas when learning moment are the definition of the term and the concept of the conservation of momentum. Even though calculations at this level are usually in one dimension, it is very important to make sure that the vector nature of momentum is stressed when the term is introduced and defined. If direction is always considered it can make it easier to avoid some common mistakes that students make when considering collisions.
It is very common for questions to all be about trucks and cars and if we leave aside the potential gender bias here there is a danger that students can see the measurement and conservation of momentum as a specific and not universal thing, so a variation of contexts is encouraged. Students will benefit from plenty of practice with describing situations as well as calculations and equations. This video clip shows momentum being conserved in space; show it with no sound and ask your students to explain what is going on.
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.
Momentum Conservation
This single sheet states what is meant by conservation of momentum and gives a worked example. There are others available on the site, for example ‘Conservation of momentum and skaters’ and ‘Impulse and momentum 1’. They can be used for notes or for short discussion activities.
Force and Motion 14-16
The section to start with here is ‘Measures of quantity of motion’ where impulse is defined and used to introduce momentum, covering Newton’s second law. The practical ‘Predicting momentum’ can lead to a good discussion on momentum being a combination of mass and velocity. Then have a look at ‘Forces replace interactions’ and do the ‘Knocking down a block’ practical. Again this leads to good discussion on momentum in collisions.
Episode 220: Momentum and its Conservation
Starting with a demonstration and discussion followed by an experiment with the air track and light gates, this would make a good introductory lesson for the topic of momentum. Although written for A level students, the nature of the subject matter means that it also works for younger students. Even the student questions would be suitable for your students.
Investigating RTAs *suitable for home teaching*
This article uses the idea of momentum together with other concepts to look at road traffic accidents and relates these to road safety. Use it as reading exercise to finish off momentum and to introduce vehicle safety in your next lesson.
