# Student power

##### Class practical

Students measure their personal power by running up a flight of stairs.

#### Apparatus and materials

Stopwatch

Metre rules, 2

Bathroom scales, calibrated in kg (or N)

Flight of stairs, not less than 3m in height, and preferably much more

#### Health & Safety and Technical notes

Those with health difficulties may need to be given other jobs to do. Check on students in advance of the lesson.

Before using this activity, the teacher must assess carefully the likelihood of the runner slipping or any other accident on stairs. If the risk is serious, consider substituting a properly-supervised climbing activity in the gym.

#### Procedure

a Measure the height of the staircase in metres.

b One student runs from the bottom to the top of the stairs, whilst another student times them with the stop-watch.

c Students who do not know their weight in newtons can use the scales to find their mass in kilograms and hence calculate their weight.

d Repeat the experiment, but with students walking up the stairs at a speed which they guess they could keep up for an 8-hour day.

#### Teaching notes

1 This experiment will generate noise and discipline problems unless it is well organized. Students will wish to compete against one another to find the 'most powerful person'. Plan in advance where students will stand and how other staff and/or students can pass by whilst the experiment is in progress.

2 Students measure their own useful power from:

Power in watts = ('weight in newtons' x height of stairs in metres) / time in seconds

Where the 'weight in newtons' = mass in kilograms x g (take g to be 10 N kg-1)

3 A very short staircase and a flying start can give astounding values of power which are quite misleading. A short burst of effort cannot be sustained. Adult males may come close to one kW for a short spurt to about 75 watts for continuous labour. So the rate of transferring energy is about the same as the energy transferred by a lamp.

Look at dietary charts (or packets of crisps or whatever) for energy transferred from food and calculate how many cream cakes it takes to climb the stairs or do a manual job for 8 hours. Or how many stairs can be climbed on one cream cake.

This experiment was safety-checked in January 2006