- principle of conservation of momentum
- calculations for one-dimensional problems
For many students, calculations of momentum and impulse will have been the most challenging encountered during GCSE. By A level it is hoped that they have a much clearer understanding of force, energy and motion but for many previous difficulties may cause anxiety. It is worth ensuring students can correctly place momentum in the context of other physical properties; units in particular can cause some difficulties. The resources listed offer one route that might be useful to consider.
It starts with some review material and progresses to quantitative experiments that students can use to check predicted changes in momentum. A distinction between perfectly elastic momentum changes - where no external forces act and there is no shift from kinetic energy to other stores - and inelastic collisions, which might involve chemical explosions or permanent shape changes.
The use of simulations is discussed and there are links to practice questions that might be useful. Discussion of causes and effects - often in the form of a flow chart - can help students understand the ideas and then describe them verbally. Thorough practice and a methodical approach to problems set in class are, for most students, the best way to achieve familiarity with the quantitative problems they will encounter in exams.
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
Several of the examples in this Catalyst article use the ideas of momentum and how this relates to road safety. It would be a good reminder of the basics or introduction to the topic.
These are straightforward calculations and A level students should be encouraged to suggest how the real data might vary from the simplified versions described here. This is a valuable opportunity to discuss how we always eliminate some complications simply to make solving a problem realistic.
As well as giving practical ideas about hands-on activities, this guidance from the IoP includes suggested difficulties and ways to address them successfully. The specific examples about why a collision/interaction might not be elastic, in terms of energy changes, are particularly useful for students. Some of the practicals may seem a little alarming to less-experienced colleagues; for example most schools no longer keep an air rifle for firing into a pendulum of known mass! There are equivalents, however, using less intimidating foam dart guns as suggested on Dr Dav's teaching blog.
The worked examples and problems will be helpful when setting consolidation questions for students.
It should be pointed out that this resource is intended to be focused on the maths, not the physics; of course with mechanics this is a technicality. The examples are sometimes a little dated but this is only apparent with comments such as Steve Ballestros as the example of a famous golfer.
The two most useful sections in terms of momentum are from p32 (about golf) and p58 (car accidents; both of those references are to the PDF, not the text itself. They include challenging content and are probably best saved for able students as extension. It should be emphasized that these are much more complex than anything they might face in the exam; instead their relevance is about seeing the context of the ideas and how specified content is extended for real-world situations.
As with the previous resource, the slightly dated nature of the commentary should not stop you using the worked examples and problems in this textbook. For example on page 67 and page 72 (PDF references) there are straightforward questions that should help all students, not just the most able, build their confidence with momentum calculations. Printing these sections is probably the best approach; the practical suggestions are reasonable but often a duplication of other resources in this list (this is not surprising as the IoP were involved in their creation).