W=Fd
Forces and Motion

Episode 213: Preparation for work, energy and power topic

Teaching Guidance for 16-19 IOP TAP

In these episodes, students can perform some useful experiments with trolleys, weights, pulleys etc. It will help if you familiarize yourself with this equipment in advance, and ensure that the wheels of trolleys and pulleys are as frictionless as possible.

Be prepared to cope with experiments where the results appear not to show that energy is conserved; this will be because of energy tranfers due to friction. Your students should appreciate that no practical system can be perfect; turn the situation to your advantage by opening up a discussion on the idea of energy efficiency.

Also in these episodes, you will find that there are opportunities for datalogging . It is impossible to provide experimental recipes which match each commercial variety of datalogger, so you will have to be prepared to adapt to the equipment available to you. Check the manufacturer’s supporting documentation for suggested experiments.

Main aims of this topic

Work, energy and power


Students will:

  • use the following equations:
    • work done = force × distance moved in direction of force.
    • change in gravitational energy = mgh
    • power = work donetime taken, power = rate of energy transfer
    • power = force × velocity
    • efficiency = useful energy transferredtotal work done × 100 %
  • understand changes in the way that energy is stored before and after an event: from energy stored gravitationally to energy stored kinetically
  • equate work done in decelerating to rest with initial kinetic energy
  • apply these ideas to situations in which vehicles and passengers are accelerated or decelerated
  • understand and use the principle of conservation of energy (as applied to mechanical energy)

Prior knowledge

Students are likely to have a simple understanding of energy, and how it is transferred by a force. They will have met the idea of conservation of energy. In these episodes, you can extend these ideas to make them more quantitative.

Where this leads

A good grounding in ideas about mechanical energy is needed before going on to a consideration of momentum.

General ideas about energy and its conservation permeate the whole of physics (and, indeed, the whole of science). Many specific results in other areas of science turn out to be examples of energy conservation, e.g. Lenz’s law in electromagnetism, Bernoulli’s equation of fluid flow.

W=Fd
involves the quantity Force Distance
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