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
- Work with a partner.
- Person A holds out their hand with a gap between their thumb and first finger.
- Person B holds the ruler with the zero at the top of person A's thumb
- Person B drops the ruler without telling Person A and they must catch it.
- The number level with the top of person A's thumb is recorded in a suitable table. Repeat this ten times.
- Swap places, and record another ten attempts.
- You can use the conversion table to help convert your ruler measurements into reaction time or just record the catch distance in cm.
| Catch distance (cm) | Reaction time (ms) |
| 1 | 50 |
| 5 | 90 |
| 10 | 140 |
| 15 | 170 |
| 20 | 200 |
| 25 | 230 |
| 30 | 250 |
| Catch distance (cm) | 1 |
|---|---|
| Reaction time (ms) | 50 |
| Catch distance (cm) | 5 |
|---|---|
| Reaction time (ms) | 90 |
| Catch distance (cm) | 10 |
|---|---|
| Reaction time (ms) | 140 |
| Catch distance (cm) | 15 |
|---|---|
| Reaction time (ms) | 170 |
| Catch distance (cm) | 20 |
|---|---|
| Reaction time (ms) | 200 |
| Catch distance (cm) | 25 |
|---|---|
| Reaction time (ms) | 230 |
| Catch distance (cm) | 30 |
|---|---|
| Reaction time (ms) | 250 |
Important: 1 millisecond (ms) is one thousandth of a second. (1/1000 s)
Example results
| Attempt | Distance on ruler (cm) | |
| With noise | Without noise | |
| 1 | 25 | 18 |
| 2 | 38 | 15 |
| 3 | 36 | 22 |
| 4 | 31 | 24 |
| 5 | 38 | 13 |
| Attempt | |
|---|---|
| Distance on ruler (cm) | With noise |
| Without noise |
| Attempt | 1 |
|---|---|
| Distance on ruler (cm) | 25 |
| 18 |
| Attempt | 2 |
|---|---|
| Distance on ruler (cm) | 38 |
| 15 |
| Attempt | 3 |
|---|---|
| Distance on ruler (cm) | 36 |
| 22 |
| Attempt | 4 |
|---|---|
| Distance on ruler (cm) | 31 |
| 24 |
| Attempt | 5 |
|---|---|
| Distance on ruler (cm) | 38 |
| 13 |
Question
What effect 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.