Quick answer: On a distance-time graph the gradient is the speed, and a flat line means the object is stationary. This Physics 9-10 lab on motion graphs gives the aim, the equipment, the safety points, a step-by-step method, sample results and 7 analysis questions; the answers are on a separate page and the lab sheet is a free printable PDF.
A graph is only useful if you can draw it from real measurements. In this lab you time a walker over marked distances, plot distance against time, and use the gradients to tell steady motion from speeding up.
Level: Physics grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: IGCSE 1.2
Aim
To plot distance-time graphs for a steady walk and a walk that speeds up, and to use their gradients to find speed and acceleration.
Equipment
- Corridor or playground at least 12 m long
- Tape measure and masking tape or chalk
- Two stopwatches or phones
- Graph paper and ruler
Safety
Walk, do not run. Check that the floor is dry and clear of bags, and stay away from doors that could open into the walker.
Method
- Mark the start line and then every 2.0 m up to 10 m.
- Run A: the walker walks as steadily as possible. Timers note the time as the walker passes each mark.
- Run B: the walker starts very slowly and walks faster and faster along the corridor, passing the last mark at about the same time.
- Record both sets of times and plot distance (y-axis) against time (x-axis) for both runs.
Results
Times recorded by one group:
| Distance (m) | Time, run A (s) | Time, run B (s) |
|---|---|---|
| 0 | 0 | 0 |
| 2.0 | 2.6 | 4.0 |
| 4.0 | 5.3 | 6.5 |
| 6.0 | 7.9 | 8.3 |
| 8.0 | 10.6 | 9.7 |
| 10.0 | 13.2 | 10.8 |
Analysis questions
Question 1 Shape of the two graphs
Describe the shape of the distance-time graph you expect for run A and for run B.Question 2 Speed in run A
Calculate the gradient of the run A graph using the points at 0 m and 10.0 m.Question 3 Speeds in run B
Calculate the speed over each 2.0 m interval of run B, to 2 decimal places.Question 4 Interpreting run B
Explain what the speeds from the previous question show about run B.Question 5 Estimating acceleration
The mid-time of the first interval is 2.0 s and of the last interval 10.25 s. Estimate the average acceleration of the walker in run B.Question 6 Reliability of the timing
The timing by hand has an uncertainty of about ±0.2 s. Calculate the percentage uncertainty in the total time for run A.Question 7 Improving the lab
Suggest two changes that would make the results more precise.
