Energy Transferred by Working
Energy and Thermal Physics

A balanced diet

Classroom Activity for 11-14 Supporting Physics Teaching

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
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.

Energy Transferred by Working
appears in the relation dU=dQ+dW
is used in analyses relating to Working Engines Thermionic Emission
is a special case of Work
has the special case Potential Energy Kinetic Energy
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