A student is investigating how the height from which a ball is dropped affects the depth of the crater it makes in a tray of sand. Explain why the student should drop the ball from each height several times and calculate a mean depth for each height.

The student should drop the ball several times at each height to identify any anomalous results or outliers that may arise from accidental variations (e.g. a slightly different release angle or a small obstruction in the sand). By repeating the experiment, any such outliers can be recognised and excluded before the mean depth is calculated. Repeating the measurements and then averaging the results reduces the influence of random error, giving a more reliable estimate of the true mean depth for each height. The mean is therefore a better estimate of the actual depth produced by that height.