- calculation of work done for constant forces, including force not along the line of motion
- calculation of exchanges between gravitational potential energy and kinetic energy
- principle of conservation of energy
The first thing to be aware of is that the recommended language for discussing energy has been changing recently. Currently the KS3 and GCSE specifications have caught up, but the students will probably not yet be familiar with it. The focus is very much on calculations, which fits very well with the quantitative approach needed at A level. The biggest change is that light, sound and current are best described as pathways or processes that explain the shifting of energy between stores. Equations can and should be used to describe the energy stored elastically, in motion and so on. For more information, the IoP's Supporting Physics Teaching resource (listed as 11-14 but current students will not have been taught in this way) is a good place to start.
When discussing work done, it is worth reminding them that energy has been shifted to another store - usually kinetic and/or thermal (work done against friction). Some will need to be reminded that lifting an object means overcoming the weight, while others will appreciate the link between Work done = force x distance and GPE = (mg)h. You may also want to revisit their use of trigonometry when forces acting at an angle to the motion are considered.
Falling objects, or objects thrown upwards to a maximum height, offer many opportunities to link kinetic and gravitational energy store calculations. Any still relying on triangles to rearrange equations will soon struggle. Doing any classroom measurements, for example with lightgates, will show how important air resistance is with most examples. Ignoring it means that the numbers do not seem to follow the principle of conservation of energy.
This principle is one that students must be able to state clearly and explain. Challenging them to justify the common phrase of 'losing energy' will help them to appreciate that rather than energy being lost or destroyed, we are often losing track of it - an important distinction. (Page 5 of this SEP resource explains it well.) Occasionally students will need to be reminded of the difference between energy conservation from a physics point of view, and the 'everyday' use which revolves around turning off lights.
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
This introductory lesson suggests questions you might use to gauge the current understanding of your class. For many the concepts will be familiar, but the practical work allows them to extend their skills while demonstrating the principles involved. The investigation guidance - with associated prompts - uses basic equipment to show a block pulled up a slope by a hanging/falling weight. This means they will need to practise resolving forces along and into a slope, a familiar exam question.
In this resource students consider what happens to the initial kinetic energy of a moving object. Links to braking vehicles are considered and there are practical guidelines for a useful investigation; you may see this as a chance to consolidate scientific vocabulary from your specification glossary.
As a quick reference to consider the combination of equations in specific circumstances, your students may find this list from SchoolPhysics useful.
In this resource it is the sequence of practical work that is important. Students are guided in reducing causes of energy 'loss', each of which results in a closer match between the calculated values. This explicit process is one they will wish to revisit for other practicals, where they can consider ways to eliminate sources of error to improve data.
At the end of the document there are problems which could be set for homework, along with model answers and explanation.