Quick answer: Conservation of energy says the total energy of an isolated system stays constant: energy changes form, such as gravitational or spring potential energy becoming kinetic energy, but is never created or destroyed. This AP Physics 1 lab on conservation of energy gives the aim, the equipment, the safety points, a step-by-step method, sample results and 8 analysis questions; the answers are on a separate page and the lab sheet is a free printable PDF.
How much power can a person produce climbing stairs? In this lab you time a climber at two different speeds, calculate the energy gained and compare the average power. It needs only a staircase, a tape measure and a stopwatch, so it works in school or at home.
Level: AP Physics 1 (algebra-based) · Curriculum: AP P1 Unit 3
Aim
To measure the gain in gravitational potential energy and the average power of a person climbing a flight of stairs at two different speeds.
Equipment
- A staircase of at least 15 steps (a school corridor or a public building)
- Metre rule or tape measure
- Stopwatch (or phone timer) and a helper
- Bathroom scales to find the climber’s mass
Safety
Use a dry, clear staircase with a handrail. Wear flat shoes with good grip. Walk down slowly after each run, never run down. Stop at once if the climber feels dizzy or short of breath.
Method
- Measure the height of one step in three places and take the mean. Multiply by the number of steps to find the total vertical height h.
- Find the climber’s mass m on the scales.
- Mark a start line level with the bottom step. The helper starts the timer when the climber moves.
- The climber walks up at a steady comfortable pace; the helper stops the timer as the climber reaches the top landing. Repeat for five trials.
- Repeat step 4 with the climber running up as fast as is safe, again for five trials.
- Rest between trials and record every time in the table.
Results
Sample data for a climber of mass 58 kg on a staircase of total height 3.50 m:
| Trial | Walking time (s) | Running time (s) |
|---|---|---|
| 1 | 14.2 | 8.2 |
| 2 | 14.8 | 7.9 |
| 3 | 14.5 | 8.1 |
| 4 | 14.6 | 7.8 |
| 5 | 14.4 | 8.0 |
| Mean | 14.5 | 8.0 |
Analysis questions
Question 1 Energy gained
Calculate the gain in gravitational potential energy of the climber in one ascent.Question 2 Uncertainty in time
For each set of trials, estimate the uncertainty in the mean time as half the range of the five readings. Express it as a percentage of the mean.Question 3 Walking power
Calculate the average power while walking.Question 4 Running power
Calculate the average power while running.Question 5 Same work, different power
Compare your two power values and explain why the energy gained is the same in both runs.Question 6 Body efficiency
The muscles of the climber are about 25 % efficient. Calculate the chemical energy used in the running ascent, and explain where the rest goes.Question 7 Sources of error
Suggest two sources of error in this lab and state whether each makes the calculated power too high or too low.Question 8 Improving the lab
Suggest two improvements that would reduce the uncertainty in the power values.
