What it shows
Average speed equals distance divided by time. Timing a short run shows differences in speed in a class, and also how reaction time of the timekeeper can add error.
The science
Average speed is total distance divided by total time. If the timekeeper starts the watch late or stops it early, the error is about 0.2 s, the human reaction time, which matters for a 5 s run. Using two timekeepers and the average reduces random errors in the data.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A flat track of 30 m marked with chalk
- Two stopwatches or phones
- A starter flag or a whistle
- A notebook
- A calculator
- Cones to mark the lines
Safety
For this project: Warm up first, run on a clear track and wear shoes. A teacher must supervise. Do not push for the fastest time; this is a speed study, not a fitness test.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Mark the start and the finish lines 30 m apart and place cones at both.
Station two timekeepers at the finish line, each with a watch.
The starter lifts the flag, and the timekeepers start the watches when it moves.
The runner sprints and each timekeeper stops their watch when the chest crosses the finish line.
Record both times and take the average for each runner.
Calculate the speed in metres per second and in kilometres per hour by multiplying by 3.6.
Make a table of the class speeds and find the mean and the range.
Draw a histogram with speeds in groups, such as 4 to 4.5 m per second.
What you should see
A histogram of speeds for the class with most students between 4 and 6 m per second. The two timekeepers’ readings differ by about 0.1 to 0.3 seconds.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is the formula for average speed?
Distance divided by time.
2How do you change m per s to km per h?
Multiply by 3.6.
3Why use two timekeepers?
It reduces timing errors.
4Why do electronic gates give better times?
They remove human reaction delay.
Take it further
Time 10 m splits to find where in a run the speed is highest.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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