Measuring reaction time with a ruler drop, turning distance into time, and analysing repeat and caffeine data.
What you will learn
- Carry out a ruler drop test with the right controls
- Calculate a reaction time with t = √(2d ÷ g)
- Spot an anomaly and calculate a mean
- Draw a fair conclusion from before and after data
The ruler drop
Your reaction time is the time between a stimulus and your response.
You can measure it with nothing more than a metre ruler:
- The catcher rests their forearm on a table edge with thumb and first finger apart, level with the zero mark of a ruler held vertically by a partner.
- The partner lets go without warning. The catcher grips it as soon as they see it move.
- Read the distance at the top of the thumb. A longer distance means a longer reaction time.
- Repeat several times, use the same hand each time, and take a mean.
Independent variable: whatever you change (for example a drink with caffeine, or practice). Dependent variable: the distance the ruler falls. Control variables: same person, same hand, same ruler, same dropper, no distractions.
The dropper must vary the moment they let go. If the catcher can guess the timing, they are not reacting at all.
The rest of this lesson and its 9 practice questions are locked.
In this lesson
- The ruler drop
- From distance to time
- Means, anomalies and caffeine
- Try it: Your first reaction time
9 practice questions, marked as you go; about 25 minutes in all.
Key terms
Anomaly
In this unit: Homeostasis and response
How the nervous and hormonal systems keep the body's internal conditions steady: reflexes and reaction time, blood glucose and diabetes, reproductive hormones and contraception, the brain, eye, temperature and kidneys, and plant hormones.