Measurement for our planet
Measurement for our planet


Measurement at home

Reaction Time

Catch me if you can!

Is your dominant hand faster or slower to react?

  • Does age affect reaction time?
  • What is gravity?

Estimated time: 20 minutes
No prior knowledge needed.


Equipment required

  • A 30 cm ruler
  • Two people
  • Use the results sheet or paper and pencil for results and calculation

Reaction time worksheet



  • Be careful not to drop ruler on people’s feet.


Watch the video

  1. Make one person Dropper, the other Catcher
  2. Catcher extends their forearm at elbow height with forefinger and thumb about 1 cm apart. Dropper holds the ruler at the top over the 30 cm at a height so Catcher has their thumb and forefinger either side of the zero cm mark.
  3. Catcher says when they are ready. Dropper then counts up, in their head, to a number between 3 and 5, using a different number each time. When the number is reached, they drop the ruler.
  4. Catcher catches the ruler as fast as possible by pinching it between forefinger and thumb. Ignore any times Catcher fails to catch the ruler.
  5. Write down the ruler cm value closest to Catcher’s pinch point, the NPL results sheet will help you record and calculate results.
  6. Do steps 2 - 5 five times and take the average.
  7. Convert drop distances to reaction times using the look up table on the results sheet, and find the range of results by subtracting the longest reaction time from the shortest one.
  8. Repeat the experiment using Catcher ’s other hand.
  9. Label results ‘dominant’ hand and ‘non dominant’ hand. (Dominant hand is the one that more comfortably holds a spoon or pencil.)
  10. Swap Catcher and Dropper roles to get more results.
  11. Enter results below.

Thoughts, tips and information

SI measurement units

  • second (s) for time
  • metre (m) for length

Challenge Topics

  • Human Biology, Measurement Science, Maths, Forces.
  1. How many measurements are needed to establish if there is a real difference in response time for your two hands? 
  2. Reaction time might also be affected by background noise, time of day and eating chocolate. 
  3. Practice can reduce reaction time by ‘training’ your body check out ‘muscle memory’. Sports people, gymnasts and dancers do this to improve accuracy of performance.

Enter your results

Please enter your results in the table below. You may enter as many results as you like. Each time you submit, cells will empty to indicate you have sent us the information.

These are optional – the age is to see if that affects reaction time, the name is so we could mention you in the end of week report and the postcode is to see where people are taking part. We won’t use this information for anything else.