Specified practical work

Plan and carry out an investigation into the effect of a factor on human reaction times

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

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. 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. The shorter the distance or time the faster your reactions.
DistanceReaction time
1 cm50 m/s
5 cm90 m/s
10 cm140 m/s
15 cm170 m/s
20 cm200 m/s
25 cm230 m/s
30 cm250 m/s

Important: 1 millisecond is one thousandth of a second.

Example results

In a second test, noise was used to distract participants from catching the ruler.

AttemptWith noiseWithout noise
125 cm18 cm
238 cm15 cm
336 cm22 cm
431 cm24 cm
538 cm13 cm

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

There is a clear difference between the 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 – 30 cm compared to without noise – 20 cm. It suggests that noise reduces the response times of the person in this experiment. [1 mark]

Tip: Include at least two or three sets of data from the results.

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