Reaction Times

• Reaction times


  An important factor in thinking distances
• Measuring reaction times with the ruler drop test

  1. Sit with arm resting on table edge

  2. Get someone to hold ruler hanging between thumb and forefinger

  3. Ruler dropped without warning

  4. Close thumb and finger to catch ruler

  5. Measure distance ruler fell

  6. Calculate reaction time from distance and acceleration due to gravity
• Reaction times


  • Typical reaction time is between 0.2 and 0.9 seconds
  • Many different factors affect reaction time
• You can't measure reaction time with a stopwatch
• Other ways to measure reaction time

  • Computer-based test (clicking mouse when screen changes colour)
  • Ruler drop test
• The longer the distance the ruler falls, the longer the reaction time
• Acceleration due to gravity is roughly 9.8 m/s²
• Calculating reaction time from ruler drop distance

  1. Use formula: v = √(2as)

  2. Where v is change in velocity, a is acceleration due to gravity, and s is distance fallen

  3. Then use formula: t = Δv/a to calculate reaction time
• The ruler drop test is hard to do accurately, so many repeats are needed
• Using a blob of modelling clay on the ruler can help it fall straight down
• Use the same ruler and have the same person drop it for a fair test
• Investigating factors affecting reaction time

  1. Introduce distractions like music or someone talking

  2. Calculate mean reaction time with and without distractions