Required practical

Reaction times

You could carry out a number of investigations to determine the effect of a specific factor on human reaction times.

A simple method to measure the effect is to use the ruler drop test.

Ruler drop test

  1. Work with a partner.
  2. Person A holds out their hand with a gap between their thumb and first finger.
  3. Person B holds the ruler with the zero at the top of person A's thumb.
  4. Person B drops the ruler without telling Person A and Person A must catch it.
  5. The distance on the ruler level with the top of person A's thumb is recorded in a suitable table.
  6. Repeat this ten times.
  7. Swap places, and record another ten attempts.
  8. You can use the conversion table to help convert your ruler measurements into reaction time or just record the catch distance in cm.
On the left-hand side two hands hold both end of a ruler from top to bottom. On the right hand side one hand has just let go and the second hand at the bottom has caught ruler.
1 cm50 ms
5 cm90 ms
10 cm140 ms
15 cm170 ms
20 cm200 ms
25 cm230 ms
30 cm250 ms
1 millisecond (ms) is one thousandth of a second.

Example results

You could carry out the experiment with and without background noise, or to investigate the effect of a drink containing caffeine on reaction time.

AttemptDistance on rulerDistance on ruler
With noiseWithout noise
125 cm18 cm
238 cm15 cm
336 cm22 cm
431 cm24 cm
538 cm13 cm

What effect does noise have on the speed of reaction, measured in centimetres? [2 marks]

There is a clear difference between length of ruler that passed through the fingers before they managed to catch it, with and without noise. [1 mark]

For example, the first set of data, with noise – an average of 34 cm was obtained, compared with 18 cm without noise. This suggests that noise increases the reaction times of the person in this experiment. [1 mark]

Tip: Calculate an average from all your data, unless there are obvious anomalous results, or outliers. If some pieces of data don't fit the pattern, exclude these from your calculation of the mean.