AQA GCSE Biology · Homeostasis & Response
Reaction time required practical
Plan and carry out an investigation into the effect of a factor on human reaction time.
A partner drops a ruler without warning and you catch it. The shorter the distance it falls, the faster your reaction. Here the factor is which hand you use.
Equipment
- Metre ruler (or 30 cm ruler)
- Table and chair
- Ruler-drop conversion table (distance to time)
- A partner
Variables
- Independent you change
- Which hand catches the ruler (dominant or non-dominant)
- Dependent you measure
- Distance the ruler falls before it is caught (converted to reaction time)
- Control you keep the same
- Same person dropping and catching
- Same ruler and starting position
- Gap between thumb and finger
- Same surroundings, with no distractions
Method
- 1
Sit with your forearm on the table and your hand over the edge.
- 2
Your partner holds the ruler vertically with the zero mark level with the top of your thumb.
- 3
Without warning, your partner drops the ruler; catch it as quickly as you can.
- 4
Read the distance (in cm) at the top of your thumb.
- 5
Repeat five times with your dominant hand, then five times with your non-dominant hand.
- 6
Calculate the mean distance for each hand and convert it to a reaction time.
Worked example
Distance the ruler fell before being caught (cm).
| Trial | Dominant hand (cm) | Non-dominant hand (cm) |
|---|---|---|
| 1 | 15 | 19 |
| 2 | 14 | 21 |
| 3 | 16 | 18 |
| 4 | 13 | 20 |
| 5 | 17 | 17 |
| Mean | 15.0 | 19.0 |
| Reaction time | 0.17 s | 0.20 s |
Working
Mean = sum ÷ number of trials: (15 + 14 + 16 + 13 + 17) ÷ 5 = 15.0 cm
From the conversion table (or t = √(2d ÷ g)): 15.0 cm → 0.17 s; 19.0 cm → 0.20 s
Conclusion
The dominant hand caught the ruler after a shorter fall, so its reaction time was faster (0.17 s against 0.20 s). This may be because that hand gets more practice, so the nerve pathways are used more.
Risks
- Falling ruler could hit feet or handsDrop it only a short way and keep feet clear.
- If testing a substance such as caffeineCheck for health conditions first and use small, safe amounts, with a teacher’s approval.
Common mistakes
- Warning the catcher before dropping. The drop must be random or they can predict it.
- Starting the zero mark at different heights. It must be level with the top of the thumb every time.
- Changing the catcher between trials. People’s reaction times vary, so use the same person.
Better results
- Repeat more times and ignore any anomalies before calculating the mean.
- Use a computer reaction test, which records time directly and is more precise.
- Have a few practice goes first so any learning effect happens before you record results.
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7 exam questions on this practical.
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