Investigating reflex actions

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

A suitable investigation could be the effect of caffeine or the amount of background noise in the room. 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 they must catch it.
  5. The number level with the top of person A's thumb is recorded in a suitable table. Repeat this ten times.
  6. Swap places, and record another ten attempts.
  7. 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.
Catch distance (cm)Reaction time (ms)

Important: 1 millisecond (ms) is one thousandth of a second. (1/1000 s)

Example results

AttemptDistance on ruler (cm)
With noiseWithout noise

What affect does noise have on the speed of reaction, measured in centimetres? Use data to support your answer. [3 marks]

When the person tried to catch the ruler without noise, they could catch it sooner than if there was noise in the background. [1 mark]

For example, the first set of data, with noise the distance was 25 cm, compared to without noise where it was 18 cm. [1 mark]

This suggests that noise increases the reaction time of the person in this experiment. [1 mark]

Tip - Make sure you include data to support your answer, as you are asked to do in the question.

Move on to Test