Reaction Time (OCR GCSE Physics A (Gateway)): Revision Note
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 is usually in the range of 0.2 - 0.9 seconds
e.g. someone waiting to react to something happening, like an athlete waiting for the start of a race
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
Examiner Tips and Tricks
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 it not required here.
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