AQA GCSE Physics

Revision Notes

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:

Measuring Reaction Time 1, downloadable IGCSE & GCSE Physics revision notes

Measuring Reaction Time 2, downloadable IGCSE & GCSE Physics revision notes

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: Jonathan

Jonathan graduated with a first-class Master's degree in Theoretical Physics from Imperial College London. He has worked in education for more than a decade as a Maths and Physics Teacher, Tutor, Head of Physics, and most recently, as Assistant Headteacher. He is now an Educational Consultant and works with us to design and improve our Physics resources.
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