Investigating reaction times (AQA GCSE Biology): Revision Notes

Investigating reaction times

What is a reaction time investigation?

Reaction time is how quickly your nervous system responds to a stimulus. Scientists can investigate what factors affect human reaction times through controlled experiments. The most common method uses a simple ruler drop test.

The core practical: effect of practice on reaction times

Aim of the investigation

The main goal is to find out if practising the ruler drop test makes people react faster. This helps us understand how the nervous system can improve with repetition.

Equipment you need

• Ruler - 1 metre long, marked in centimetres
• Partner - to work with during the experiment
• Data table - to record your measurements

Method: step by step

Setting up:

1. Sit on a stool with your weaker hand resting on the bench
2. Let your hand hang over the edge of the bench
3. Open your thumb and forefinger ready to catch

During the test: 4. Your partner holds the ruler upright so the 0cm mark lines up with the top of your thumb 5. Focus straight ahead across the lab, not at the ruler itself 6. Your partner drops the ruler without warning 7. Catch the ruler as quickly as possible using your thumb and forefinger

Recording results: 8. Read where the top of your thumb is on the ruler (to the nearest cm) 9. Repeat this test 2-5 times for each person 10. Swap roles so both people get tested

Important tips for accurate results

Recording your data

Create a table like this to organise your measurements systematically:

Drop number	Reading (cm)	Reaction time (ms)
1
2

Calculating reaction time

The formula

When a ruler falls, it accelerates due to gravity. Scientists have worked out this formula using physics principles:

$\text{Reaction time in ms} = \sqrt{2000 \times \text{cm}}$

Example calculation

Remember: Always round your final answer to 2 significant figures (like 390ms in this example).

Why this formula works

The ruler falls at a constant acceleration because of gravity. The further it falls, the longer you took to react. The square root relationship comes from physics equations about falling objects under constant acceleration.

Analysing your results

Processing the data

1. Convert measurements: Use the formula to change each cm reading into reaction time
2. Create a bar chart: Put reaction time on the vertical axis and drop number on the horizontal axis
3. Look for patterns: Describe what your results show about the effect of practice

What you might find

• Reaction times often get faster with practice
• The improvement usually levels off after several attempts
• Individual differences exist between people

Other investigations you could try

Scientists can investigate other factors that affect reaction times:

• Caffeine: Does drinking cola or coffee make you react faster?
• Exercise: Do reaction times change after physical activity?
• Age: How do reaction times compare between different age groups?

Safety considerations

Remember!