20 m Sprint Timed Frame by Frame

Groups of three time 20-meter sprints two ways at once: with a stopwatch and by filming in slow motion to count frames. Comparing the two shows how much error hand timing has and gives reliable data for tracking speed.

How to play

1. Sprint-specific warm-up: skipping, butt kicks and build-up runs of 10 and 15 meters (5 min).
2. Groups of three: runner, hand timer at the finish and a filmer shooting slow motion at 120 or 240 frames per second, standing about 15 meters away at a right angle so the start and finish cones are both in frame (3 min).
3. Each runner does three sprints with 2 minutes of walking recovery; each sprint is filmed and hand-timed at the same time, and roles rotate (12 min).
4. On the video, count the frames from the first foot movement to the torso crossing the finish line, then divide by the frames per second (6 min).
5. Record both times on the worksheet, work out the group's average difference and explain why they don't match (4 min).

Rules

• Leave a clear stopping zone of at least 30 feet past the finish.
• The filmer and timer always stay outside the lane.
• No one sprints before finishing the warm-up.
• Only film the current runner, and delete the videos at the end of class.

Variations

Adaptations

• Wheelchair user: sprints in the chair on a smooth lane; the calculation is the same.
• Lower-limb injury: takes the analyst role and works out the times for the whole group.
• Low fitness level: does two sprints with longer recovery and compares only against their own times.

Learning goals

• Measure speed with a method more accurate than a stopwatch.
• Calculate and explain measurement error.
• Apply acceleration technique over short distances.

Equipment for a class of 25

• tablets or phones: 9
• cones: 18
• stopwatch: 9
• worksheets: 28

Teacher tip

At 240 frames per second each frame lasts about 4 thousandths of a second, but at 30 it's over 3 hundredths, so check each phone's settings before starting. Hand times usually come out faster because of the delay in pressing at the start.

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