# 5.8.3 Reaction Time

### Measuring Reaction Time

• The reaction time is defined as:

A measure of how much time passes between seeing something and reacting to it

• The human reaction time for someone who is alert – i.e. someone waiting to react to something happening, like an athlete waiting for the start of a race – is usually in the range of 0.2 – 0.9 seconds
• A simple method for measuring human reaction time is illustrated below:

Dropping a ruler provides a simple and fun way of measuring someone’s reaction time

• Person A holds a 30 cm ruler vertically, such that the bottom end of the ruler hovers over the top of the hand of Person B
• Person A should release the ruler unexpectedly
• As soon as Person B sees the ruler move, they should close their hand, catching it
• The ruler is marked at the point at which it was caught by Person B – i.e. in line with the top of their hand
• This gives a measurement of the distance the ruler fell
• The greater the distance, the longer the reaction time

### Author: Ashika

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.
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