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Energy Transferred by Working
Energy and Thermal Physics

Paying for getting things done - Teaching approaches

Classroom Activity for 11-14

A Teaching Approach is both a source of advice and an activity that respects both the physics narrative and the teaching and learning issues for a topic.

The following set of resources is not an exhaustive selection, rather it seeks to exemplify. In general there are already many activities available online; you'll want to select from these wisely, and to assemble and evolve your own repertoire that is matched to the needs of your class and the equipment/resources to hand. We hope that the collection here will enable you to think about your own selection process, considering both the physics narrative and the topic-specific teaching and learning issues.

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A balanced diet

Energy Transferred by Working
Energy and Thermal Physics

A balanced diet

Classroom Activity for 11-14

What the Activity is for

Calculating energy intake and energy needs.

To establish that energy can be measured in joules and that having available too few joules to shift limits what one can do.

What to Prepare

  • a collection of food labels, showing energy per 100 g marked in joules, or a nutrition data table showing energy per 100 g only
  • a diary of a day's activity for the pupil, showing the number of minutes spent on each activity for one 24-hour period

What Happens During this Activity

This activity could usefully be carried out with spreadsheets, using technology to help keep track of the calculations.

Get each pupil to think about their energy needs first by getting each one to identify their different periods of activity during the 24-hour period, and then mapping theses according to the following categories.

activityenergy for each minute / kilojoule
sleeping5
sitting6
standing7
washing, dressing15
walking slowly13
walking moderately quickly21
walking up and down stairs38

Pupils should choose one of these for each period of activity, choosing the activity that they think most closely matches their actions. Then they can now calculate their energy demand for the day.

Next the pupils should map out their food intake for the 24-hour period and use the food labels to work out their total energy input during this time. Do their energy input and output figures indicate a balance?

With their energy balance figures at hand, it is interesting to discuss the effects of going into an energy surplus or deficit over the longer and shorter term.

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Paying for joules at home

Power
Energy and Thermal Physics

Paying for joules at home

Classroom Activity for 11-14

What the Activity is for

Exploring energy use in the home.

To establish that domestic appliances use energy at different rates and give rise to different financial costs.

What to Prepare

  • a collection of power ratings for domestic appliances.
  • a diary of a day's activity for the appliances, showing the number of seconds that it was used for during one 24-hour period.
  • a copy of a current electricity bill for you region, showing the cost for one unit (3.6 megajoule)

What Happens During this Activity

This activity could usefully be carried out with spreadsheets, using technology to help keep track of the calculations.

First explain that the power ratings on the appliances give the number of joules to be paid for one second of use. Then show how to find the total number of joules to be paid for, by multiplying the number of joules per second (the power) by the number of seconds. You'll need to take some care here, as many appliances will have a power in kilowatt, so thousands of joules a second.

Then compile a table of the number of joules to be paid for, and work out the costs for each appliance, using these rows headings for each appliance: appliance power/watt; time used/second ; energy cost/joule; money cost/pound.

Draw special attention to the way in which the common currency of joules allows the pupils to compare very different things such as the cost of ironing with the cost of running a hair-dryer, for example.

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One week's journeys

Energy Transferred by Working
Energy and Thermal Physics

One weeks' journeys

Classroom Activity for 11-14

What the Activity is for

To investigate the energy costs of travel.

To establish that energy is measured in joules and that some kinds of travel are more expensive than others.

What to Prepare

  • a diary of a week's travel activity for a pupil, showing the number of kilometres travelled by each mode of transport.

What Happens During this Activity

This activity could usefully be carried out with spreadsheets, using technology to help keep track of the calculations.

Draw up a table of the number of kilometres for each mode of travel and use this to find out how many joules have been expended for each one:

energy cost for one person to travel one kmkilojoule
bicycle65
walking232
running287
moped371
car (1 person – 30 mph)2264
car (5 people – 30 mph)506
car (1 person – 60 mph)3444
car (5 people – 60 mph)767
train470

Look for common patterns and differences among the pupils. You could make this into something of an exercise in the analysis of data: what hypotheses might explain the patterns?

Again, draw special attention to the way in which the common currency allows pupils to compare very different modes of transport.

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Choosing household lighting

Energy Transferred by Working
Energy and Thermal Physics

Choosing household lighting

Classroom Activity for 11-14

What the Activity is for

To establish that individual choices can make a difference, eg when comparing lamps.

What to Prepare

  • two mains lamps of equal brightness, one energy saver (compact fluorescent) and one filament, say 100 watt, complete with their packaging
  • this interactive (see below)

What Happens During this Activity

Compare the brightness of the two lamps. They should provide equal illumination, but the conventional filament lamp will cost more energy per second to run (about four times as much typically). Now compare how warm they feel by holding the hand a short distance away.

Show the interactive.

Making savings

Work out with the class how many such lamps they have in their homes. What savings could be achieved if they all swapped? Now work it out for the whole school. This will be a very good practice of estimating – always work to one significant figure only! How many people have to change so that we can shut down one 100 MW power station? Perhaps we could avoid all the arguments about wind turbines in remote areas of natural beauty if we all demanded a bit less energy.

Lamps are easy to compare as most homes are lit using electrical power. Whilst it would be very useful to compare lighting with heating, it'll only be a minority of homes that are all-electric, and so such comparisons are harder to do without much more conversion work. However, if your class can cope with the numbers and arithmetic, this is well worthwhile, if only to convince them that turning a light off to save energy is not the most effective of actions.

Resources

Download the interactive for this activity.

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