Three Stopwatches, One Time: Measurement Error

In each 30 m sprint, three students time the same runner at once and compare their times. The group discovers human timing error, how it changes with the start signal, and why the median is used.

How to play

1. Progressive warm-up with high knees and two 20 m build-ups (5 min).
2. Round 1: three timers at the finish clock each runner on a voice start; record all three times (6 min).
3. Round 2: the start signal is a dropped scarf; record all three times again (6 min).
4. Group math: the middle time (median) and the gap between the highest and lowest time for each sprint (4 min).
5. Conclusions: which signal makes the stopwatches agree more, and is it fair to compare hand-timed results? (4 min).

Rules

• Timers stay at the finish line and out of the lanes.
• Run in separate lanes and slow down in a straight line after the finish.
• Times are only for studying error, not for rankings.
• Anyone who doesn't want to run can time every round.

Variations

Adaptations

• Students with visual impairments: time using the voice start and hear the finish from the finish judge's clap.
• Limited mobility: take part as a timer, or race in a wheelchair on a wide, flat lane.
• Students who struggle with math: put the three times in order on a card and point to the middle one.

Learning goals

• Improve acceleration and short-distance speed.
• Understand measurement error and how to reduce it.
• Think about fairness when measuring sports results.

Equipment for a class of 25

• stopwatches: 9
• cones: 8
• log sheets: 3
• scarves: 3

Teacher tip

With a voice start, timers usually react late, so the time comes out short; with the scarf they agree more. Stopwatch apps on tablets work fine if you don't have handheld stopwatches.

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