AQA Biology 4.5.2.1 · Combined 4.5.2
Reaction time
Drop a ruler, catch it, and turn the distance into a time. Then test whether one factor changes it.
Triple Science · Higher tier
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Catch!
Someone knocks a phone off the table and you grab for it.
If you had to guess, are you quicker to catch it when you’re wide awake, or when you’re tired?
Biology required practical 7
The ruler drop.
Reaction time is the time between a stimulus and your response. A partner holds a ruler vertically with 0 cm level with the top of your thumb and finger. Without warning, they drop it; you catch it. Read the distance at the top of your thumb. The longer the distance, the longer the reaction time. Test one factor: distraction, by doing mental arithmetic while you catch.
Pick a condition, then drop the ruler three times.
The conversion table turns a distance into a time. Check its units: here distance is in cm and time in s.
Planning one? Tap each part.
Typical reaction times range from 0.2 s to 0.9 s; for a simple stimulus like this, about 0.2–0.3 s. Alcohol, tiredness and distraction slow reactions; caffeine is a stimulant and speeds up the nervous system. The pathway itself: The nervous system.
Method · mean of repeats
mean = total of the repeats ÷ number of repeats
Written out
Measurements are affected by random error: results vary in unpredictable ways. Repeating and reporting a mean reduces the effect. Put every repeat in the same unit first: ms ÷ 1000 gives s, so 240 ms = 0.24 s. A distance in m or mm must go into cm before you use the table: m × 100; mm ÷ 10, so 120 mm = 12 cm.
Think again · further means faster?
“Further down the ruler means faster reactions.”
Your call
ChoosePupil A catches the ruler at 12 cm. Pupil B catches it at 30 cm. Who reacted faster?
Sort
Which variable?
Distraction investigation. Place each one.
Tap a card, then tap the box it belongs in. Tap a placed card to take it back.
Command words in this lesson
- Plan
- Variables, method, repeats, safety and ethics, and how you’ll show the results.
- Calculate
- A mean, with every repeat in the same unit.
- Use the table
- Distance to time, units checked first.
Key fact
A longer catch distance means a longer reaction time. Read times from the conversion table, repeat, and report a mean.
Key note · AQA 4.5.2.1 (Combined 4.5.2) · RP 6 / RP 7
Reaction time
- Reaction time: the time between a stimulus and a response. Typical values 0.2 s to 0.9 s; about 0.2–0.3 s for a simple stimulus.
- Ruler drop: 0 cm at the top of the thumb, drop without warning, read the catch distance. Longer distance, longer time.
- Use the conversion table, units checked. Repeat and report a mean to reduce random error.
- Change one factor, control the rest, act safely and ethically, and show the means as a bar chart.
Photograph this card. Tomorrow, cover it and say each line first.
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Not sure which unit the table wants?
Catch distances and the conversion table are teaching values.