Nervous System (AQA GCSE Biology Combined Science): Revision Notes
Required practical - Investigating reaction times
What is this practical about?
This practical lets you investigate how different factors affect human reaction times. You'll mainly focus on how practice affects how quickly someone can react, but you could also test other factors like caffeine or exercise.
Reaction time is the time it takes for your nervous system to detect a stimulus and respond to it. This practical uses a simple falling ruler method that's been used by scientists for decades to measure human response times.
Aim
The main goal is to investigate the effect of practice on human reaction times. You want to see if people get faster at reacting when they do the test multiple times.
Equipment you need
You only need simple equipment for this practical:
- A ruler that's 1 metre long, marked in centimetres
- A partner to work with
You might also get a ruler with a paper scale that already shows reaction times, or a table to help you convert your readings.
Method - step by step
Here's exactly how to do the test:
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Set up your position: Sit on a stool with your weaker hand's forearm resting on the bench. Let your hand hang over the edge.
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Prepare to catch: Open your thumb and forefinger. The ruler will fall between them, and you'll need to catch it.
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Partner holds the ruler: Your partner holds the ruler upright so the 0 cm mark is level with the top of your thumb.
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The drop: Without warning you, your partner lets go of the ruler. Catch it as quickly as you can using just your thumb and forefinger.
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Record the measurement: Write down the reading on the ruler where the top of your thumb is, to the nearest centimetre.
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Repeat the test: Do steps 2-5 ten times in total.
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Swap roles: Change places with your partner and repeat steps 1-6.
Critical Setup Points:
- If you're right-handed, use your left hand (your weaker hand) for more consistent results
- Sit up straight and focus across the lab, not on the ruler itself
- The ruler should lightly touch your thumb so you can feel when it starts to drop
- Don't do any practice before starting - this would affect your results
Recording your results
Create a table like this to record your measurements:
| Drop number | Reading in cm | Reaction time in ms |
|---|---|---|
| 1 | ||
| 2 | ||
| ... |
Make sure to record your readings immediately after each drop to avoid forgetting the measurements. You'll convert the distance readings to reaction times later using the formula.
Calculating reaction time
The ruler falls because of gravity at a constant acceleration. You can convert the distance in centimetres to reaction time in milliseconds using this formula:
Worked Example: Converting Distance to Reaction Time
If the ruler falls 75 cm:
Step 1: Apply the formula
Step 2: Calculate inside the square root
Step 3: Find the square root
Step 4: Round to 2 significant figures
Remember to give your final answer to 2 significant figures (like 390 ms in this example).
Analysis
After collecting all your data:
- Convert all readings to reaction times using the formula or a conversion table
- Plot a bar chart with:
- Reaction time on the vertical axis
- Drop number on the horizontal axis
- Describe what your results show - do reaction times get faster with practice?
Other variables you could investigate
Alternative Investigations
Instead of practice, you could test:
- The effect of caffeine (having a cola drink)
- The effect of exercise
- Differences between dominant and non-dominant hands
Each of these variables could provide interesting insights into factors that affect human reaction times.
Key Points to Remember:
- Practice usually improves reaction times - people get faster with repetition
- Use the weaker hand for more consistent results
- The formula is: reaction time in ms =
- Don't practice before starting the real experiment
- Always give your final answers to 2 significant figures
- Repeat the test multiple times to make your results more reliable