Catch it!


This experiment tests your reactions. Try it with a friend to find out if you're half asleep or superhero material!


It takes time for you to react. Messages travel from your eyes, along your optic nerves into your brain. These messages then travel from your brain back down to your hands. Nerve impulses travel at anything between 1 and 120 metres per second, so your reaction time can never reach zero! The experiment tests how long it takes these messages. The brain is translating visual information (falling ruler) into the voluntary (or conscious) motor commands and actions (grasping finger movements) that lead to the ruler being caught. The shorter the time, the faster your reactions.

Practice will specifically affect the ‘associative centres’ in the brain, so that you can respond faster to what’s happening in your visual world. Falling rulers in this case. The flow of information along the ‘visual’ and ‘motor’ nerve pathways is relatively constant even with lots of practice. It all comes down to ‘attention’ or ‘…being on the ball!’

You will need:

  • 30cm ruler
  • Friend
  • Results pdf document


  1. The experimenter holds the ruler at the top (30cm mark)
  2. The subject gets ready to catch the ruler by placing their index finger and thumb either side of the 0cm mark. They must not touch the ruler.
  3. The experimenter drops the ruler. Make sure you give no clues as to when you will do it. The subject must try to catch it as fast as possible.
  4. Note down the measurement just above the subjects first finger where the ruler was caught.
  5. Repeat five times, then take the average reading by adding up all the results and dividing by five.
  6. Swap places and repeat the experiment.
  7. Look up your results on our table.


  • How do you convert the distance to time?

    You can calculate your own reaction time using the following equation:

    t=√(2 x d ÷ 9.8)

    Where d = distance in metres, t means time. Incidentally, 9.8 is the acceleration of the ruler by Earth's gravitational pull, so if you're trying this elsewhere you will have to use a slightly different figure!

    The formula above came from the common displacement/acceleration equation used in physics:

    d = v0t + ½at2

    Where v0 = initial velocity (m/s), as the ruler was not moving before it was dropped v0 is 0. We already have a as the Earth's gravity, so the formula becomes:

    d = ½ x 9.8 x t2

    To simplify it we multiply both sides by 2 to get:

    2 x d = 9.8 x t2

    Then we can divide both sides by 9.8 to get:

    2 x d ÷ 9.8 = t2

    And finally, we take the square root of both sides to find t:

    t = √(2 x d ÷ 9.8)

  • What can I try next?

    Here’s a few suggestions for your next experiment; do reaction times vary for people of different ages (children versus adults), if you use your dominant hand versus non-dominant hand, if you are tired or alert (try a caffeinated drink), for men or women, depending on your mood or after an alcoholic drink (this one is for adults!). Why not send us your experiment design and conclusions?