Grade 11 · ⚛️ Physics · Mechanics · PHY-G11-M1.1
Measure your own walking speed
Time yourself over 10 metres at three different paces and calculate real velocities with v = Δx / Δt.
Why this matters
A minibus driver on Bole Road has to brake before a pedestrian crossing — but how far ahead? At 50 km/h, the bus needs about 35 metres to stop safely. Engineers calculate that with exactly the formulas in this experiment: v = Δx/Δt, then a = Δv/Δt for the brakes. The same idea sets bus schedules and decides where speed bumps go.
Watch the demo
Video by FuseSchool
The science
Position vs. displacement
Position is where an object is on a chosen axis — a coordinate x. Displacement is the change in position, Δx = x_final − x_initial. Distance is the total path length, which can be larger than the magnitude of displacement if the object turns around.
Velocity vs. speed
Average velocity v_avg = Δx / Δt is a vector — it has direction. Average speed is the total distance divided by time and is always non-negative.
Acceleration
Acceleration is the rate of change of velocity: a = Δv / Δt.
You'll need
- A flat 10-metre path (yard, hallway, or schoolyard)
- A phone with a timer or a wristwatch
- Chalk or tape to mark start and end
- A tape measure↳ Or a string you've marked every metre
Safety first
- Use a path away from traffic.
- When walking fast, watch out for obstacles.
Step by step
0/4 doneWhat you should see
Your three speeds differ clearly — something like 0.8, 1.3 and 2.0 m/s.
Why it happens
Because you walked in one straight line in one direction, your displacement equals your distance, so your average speed equals the magnitude of your average velocity. You've measured a real-world v = Δx / Δt with your own feet.
Didn't work? Try this
My times vary a lot between tries at the same pace.
Reaction time adds error. Use a longer path (20 m) or average three runs at each pace.
I got a speed above 3 m/s while walking.
Check your distance and that the timer started at the start line, not after it.
Still stuck? Ask the lab assistant
Check your understanding
1. A student walks 100 m east, then 40 m west. What is the magnitude of displacement?
2. Which quantity is always non-negative?
Your lab notebook
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