Interactive practical

Personal power

Weigh a climber, measure the height of a flight of stairs, time walking and running up it by hand, and calculate the work done and the power.

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GCSE Physics

Measuring personal power

CCEA 1370 — matched to your course.

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Practical focus

Estimate mechanical power from the gain in gravitational potential energy during stair climbing or repeated step-ups.

Practical method

Aim

Estimate your useful power output when running up stairs, P = \(\dfrac{\text{mgh}}{t}\).

Variables

Independent variable: the activity or person (or the speed of climbing)
Dependent variable: power output
Control variables: the same staircase (same vertical height); the same timing method; starting from rest at the bottom.

Apparatus

Bathroom scales
Metre rule or tape measure
Stopwatch
A safe staircase

Method

Measure your mass on the scales.
Measure the height of one step and count the steps to find the total vertical height h.
Time how long it takes to walk or run up the stairs safely.
Calculate the gain in gravitational potential energy E = mgh and power P = \(\dfrac{E}{t}\).
Repeat three times and use a mean time.

Sample results

A 60 kg student climbs 15 steps of 20 cm (h = 3.0 m); g = 9.8 N/kg.

Trial	Time / s	Power / W
1	4.9	360
2	4.7	375
3	4.8	368
Mean	4.8	368

Analysis

E = mgh = 60 × 9.8 × 3.0 = 1764 J. With a mean time of 4.8 s, P = 1764 ÷ 4.8 ≈ 368 W, about 370 W. This is the useful power that increases gravitational potential energy; the body's total power is much higher because energy is also transferred to thermal stores.

Errors and improvements

Problem	Effect	Improvement
Reaction time when starting and stopping the stopwatch	Time uncertain by about 0.2 s	Use a longer staircase or light gates
Measuring along the slope instead of vertically	Height too large, power too large	Measure vertical step heights
Scales read in kg not newtons	Wrong weight if g is forgotten	Multiply mass by g = 9.8 N/kg

Risk assessment

Hazard	Risk	Control measure
Running on stairs	Tripping and falling	Walk briskly rather than run; keep the staircase clear; use the handrail
Overexertion	Feeling unwell	Stop if unwell; take part only if fit to

Common mistakes

Using the diagonal length of the stairs.
Forgetting to multiply mass by g.
Using minutes instead of seconds.

Worked analysis

A 55 kg student climbs 2.5 m in 5.0 s. E = 55 × 9.8 × 2.5 = 1347.5 J; P = 1347.5 ÷ 5.0 ≈ 270 W.

Common misconception

Running up the stairs faster does not increase the energy needed; it increases the power, because the same energy is transferred in less time.

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