Required Practical: Reaction Time

In this practical, we are investigating the effect of a factor on human reaction times.

A simple test that investigates reaction times is the ruler drop test. This practical involves two people (person A and person B) working as partners.

1. Person A sits upright on a chair and places their dominant arm across the table, with their hand hanging over the edge of the table

2. Person B holds the ruler vertically, with the zero mark at the top of person A’s thumb

4. At a random time, person B drops the ruler for person A to catch

5. Person A catches the ruler as fast as they can, with their thumb and first finger

6. Person B records the measurement on the ruler in a table, such as the one below

AttemptDistance (cm)

7. The test is repeated several times

8. Person A swaps places with person B to test the reaction time of person B

  • This allows us to compare reaction times

9. Calculate the mean from the experiments and convert the result values to reaction time using a conversion table, such as the one below.

Distance (cm)Reaction time (s)
  • The lower the number is, the faster the reaction time

We can use the conversion table to complete the results table

AttemptDistance (cm)Reaction time (s)

In this experiment, the variables we should keep constant are:

  • Measuring the ruler from the top of the thumb each time
  • The distance between the thumb and the first finger
  • The hand used to catch the ruler
  • The room conditions (e.g. lighting and background noise)

If the control variables change, this can affect the dependent variable, which is the reaction time.

Investigating Other Variables

We can alter the experiment to investigate other independent variables. For example, we can investigate the effect of practice on reaction times. To do this, person A can catch the ruler many times, while person B records the results. We can then look at the results to see if the reaction times get faster with an increase in the number of tries.

We can investigate the effect of different chemicals on reaction time. For example, measuring the reaction time before and after drinking a caffeinated drink.

Before taking a caffeinated drinkAfter taking a caffeinated drink
Reaction time 1 (s)
Reaction time 2 (s)
Reaction time 3 (s)
Mean time (s)

We can also investigate whether using a dominant or non-dominant hand will affect reaction times. We use our dominant hand more, so we might expect reaction times to be faster with our dominant hand compared to our non-dominant hand.