Motion: describe how to measure distance and time in a range of scenarios

The idea

Measuring motion means choosing a method that suits the scale and setting. For a trolley on a bench, use a metre rule or tape for distance and light gates or a stopwatch for time. For a falling object, use a ruler or metre rule for drop height and light gates or a slow-motion camera for short time intervals. For a runner on a track, use a tape or marked track for distance and a stopwatch or timing gates for time. For a toy car down a ramp, mark start and finish lines, measure the length with a tape, and time with a stopwatch or light gates. Match the instrument to the quantity, repeat readings, and reduce reaction-time error by using electronic timing where possible.

What earns the marks

• Selects an instrument suited to the distance, such as a metre rule, tape measure or marked track.
• Selects a timing method suited to the interval, such as a stopwatch, light gate or timing gate.
• Describes marking clear start and finish points so the distance measured matches the time measured.
• Explains how to reduce timing error, for example by using electronic timing or repeating readings.

Common mistakes and how to put them right

• Uses a stopwatch for very short intervals where reaction time dominates.

  Put it right: Use light gates or a camera instead.

• Measures distance along a different path from the motion timed.

  Put it right: Align start and finish markers with the timed section.

• Reads a ruler from the end rather than from a clear scale mark.

  Put it right: Measure between two marked points.

• Takes a single reading and treats it as reliable.

  Put it right: Repeat and average to reduce random error.

Exam tips

• Name the instrument and say what it measures in each scenario.
• State how start and finish are defined so distance and time refer to the same motion.
• Mention one improvement that reduces error, such as light gates or repeats.
• Keep units consistent, using metres and seconds.