2.4.2 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
• 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
• Exam Tip

  The method described here is a standard method for measuring reaction time, however there are numerous other methods possible, so don't be surprised if you are given a situation that you are not familiar with. Notice that this method does not directly measure a time. The distance that the ruler has fallen can be used to calculate a time accurately, but that is not required here.