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 notesMeasuring 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

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