Investigating Factors Affecting Reaction Time (WJEC GCSE Biology: Combined Science)

• Reaction time is the time taken to respond to a stimulus; reactions are usually very quick responses typically taking less than a second to occur
• Reaction time can be affected by factors such as age, stress or use of drugs (such as caffeine)
• In this practical, you will investigate the hypothesis that reaction time improves with practice
• Reaction time can be measured in this way using the principle that the further down the length a ruler is caught, the slower an individual's reaction time
• The experiment can be repeated several times to calculate a mean average distance caught and this can be equated to a reaction time

Variables

• Independent variable - the person catching the ruler
• Dependent variable - reaction time (measured using catch distance on a ruler)
• Control variables should be considered in this experiment such as:
  • The person catching the ruler using their dominant hand each time
  • Dropping the same ruler from the same height and angle each time, with the ruler orientated in the same direction (0 cm facing down)
  • Ruler size

Apparatus

• 30 cm ruler
• Volunteers x5

Method

1. Each volunteer needs to sit in a chair with a good upright posture 
2. Ensure the volunteer places their forearm on the table so that it extends over the edge 
3. Ask the volunteer to place their thumb and fingers finger on either side of the bottom of the vertically placed ruler with the number “0” at the bottom and the “30” near the top
4. Tell the volunteer that the ruler will be "dropped" without warning. The volunteer needs to catch the ruler with their thumb and forefinger as soon as they sense it dropping
5. Drop the ruler. When your volunteer catches it, record the number on the ruler displayed just over the thumb. The lower the number, the faster the reaction time
6. Conduct five trials with the same volunteer
7. Repeat the experiment with at least four other volunteers and record your results in a suitable table. Use a conversion table to convert the measurements into reaction times

Reaction time diagram

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

Analysis and evaluation

• The conversion of the ruler drop measurement in cm to a reaction time is an example of translating data from one form to another
• You should discuss the extent to which your results support the hypothesis that reaction time improves with practice
• An evaluation of this practical may include suggestions and changes to the method such as:
  • Using a computer to record reaction times; this is more accurate as it removes human error from measurements
  • Reaction time can also be recorded in milliseconds which is more precise than in seconds
• There are sources of error in this practical which include:
  • An inability to see exactly where on the ruler the volunteer's fingers catch the ruler
  • The ruler is not being placed in the same position above the volunteer's fingers each time