Reaction Time Experiment: The Ruler Drop Test (with Mean, Median and Range)

How quickly can you react? A ruler, a partner and about twenty minutes are enough to measure it, and to practise the statistics that turn raw numbers into a conclusion.

The ruler-drop test

You need: a 30 cm ruler with clear centimetre marks, a partner, a calculator and a data table.

Your partner holds the ruler vertically, with the 0 end between your thumb and finger, but not touching.
Without warning, your partner lets go. You catch it as fast as you can.
Read the number at the top of your thumb. That’s how far the ruler fell, in cm.
Do five catches with your writing hand, then five with your other hand.

A shorter distance means a faster reaction.

Turn the numbers into a conclusion

Suppose a student’s catches (in cm) with their writing hand are 14, 16, 12, 15, 13, and with their other hand are 19, 22, 17, 21, 18.

Mean: add and divide. Writing hand: (14 + 16 + 12 + 15 + 13) ÷ 5 = 14 cm. Other hand: (19 + 22 + 17 + 21 + 18) ÷ 5 = 19.4 cm.
Median: the middle value when ordered. Writing hand: 12, 13, 14, 15, 16, so 14. Other hand: 17, 18, 19, 21, 22, so 19.
Range: biggest minus smallest. Writing hand: 16 − 12 = 4 cm. Other hand: 22 − 17 = 5 cm.

Claim: my writing hand reacted faster. Evidence: it averaged 14 cm versus 19.4 cm, and even the slowest writing-hand catch (16 cm) beat the fastest other-hand catch (17 cm). Reasoning: the writing hand is more practised at fine control.

That last piece of evidence, where the ranges barely overlap, is what makes the claim strong. If the ranges overlapped heavily, you’d say the difference might not be real.

Pool the class data

Plot each student’s mean on a class line plot with dots. Look at the shape. Is it clustered or spread? Does the class result agree with individuals? A bigger sample gives a more reliable answer.

What’s happening in your body

When your partner lets go, your eyes see the ruler fall. The signal travels to your brain, then your brain sends a signal along nerves to the muscles in your fingers. That journey takes time. It’s usually about 0.15 to 0.25 seconds, and a ruler falls about 11 to 31 cm in that time. Dropping a ruler is a rough clock based on gravity: the longer it falls, the farther it drops.

Make it fairer

Don’t let the catcher watch the partner’s hand.
Vary the time between “ready” and the drop so it can’t be guessed.
Use the same ruler and the same starting spot every time.
Keep distractions out: no talking.

What next?

Use the class numbers to practise graphing. Our lesson Which graph tells the truth? shows how the same numbers can be drawn honestly or misleadingly. The reaction-time test itself is How fast are our reaction times? in the Data Detectives unit. For mean, median, mode and range practice, our free pack is Mean, Median, Mode and Range. Sign up for three lessons free.