3-NRG-03

Outcomes

• Pupils understand that work done is energy transferred.
• Pupils can draw and complete Sankey diagrams of energy transfers.
• Pupils understand that power is the rate of doing work.
• Pupils can perform simple calculations of work done and power developed.

Specification References

4.5 describe a variety of everyday and scientific devices and situations, explaining the fate of the input energy in terms of the above relationship, including their representation by Sankey diagrams

4.9 recall and use the relationship between work, force and distance moved in the direction of the force: work done = force × distance moved, W = F × d

4.10 understand that work done is equal to energy transferred

4.13 understand how conservation of energy produces a link between gravitational potential energy, kinetic energy and work

4.14 describe power as the rate of transfer of energy or the rate of doing work

Main Body of Lesson

• Remind pupils of their previous work on energy transfers and the conservation of energy.
• Explain that transferring energy from one form to another is the process of doing work.
• State formula for calculating work done = force × distance.
• Pupils calculate the work done dragging a wooden block across their benchtop.
• Introduce equation for calculating (change in) gravitational potential energy as a form of the work done equation.
• Give pupils examples where the same amount of work is done in different amounts of time (e.g. riding a bike up the same hill quickly and slowly).
• Introduce the concept of power as the rate of doing work (i.e. power = work done / time taken). A more powerful device is able to convert energy from one form to another quicker than a less powerful device.
• Pupils calculate the power they developed in the previous running-up-and-down-the-stairs task.
• Pupils draw a Sankey diagram for their travels up stairs.

Practicals/Demonstrations

• Pupils use newtonmeters to calculate work done (against friction) as they drag a wooden block across the benchtop.
• Pupils calculate the work done and the average power developed as they (repeatedly) climb a set of stairs.

Plenary

• Pupils sort a range of household devices (e.g. television, washing machine, power shower, oven, iPod, etc) into order of power consumption (slide available).

Additional Information

Resources Required

• Newtonmeters
• Wooden blocks with hooks

Safety/Hazards

• Overstretched newtonmeters can be hazardous.

Energy Outline

Energy (3rd Form)