Extra Credit Project: The Reaction-O-Meter

What is the average reaction time of a human being?

This project must be done by individuals.

Your job is to construct a Reaction-O-Meter: a device which permits you to measure the interval between the time a person sees a motion and the time he reacts to it. The basic idea is as follows: one person (the "observer") holds a ruler-like piece of cardboard so that it hangs down vertically; a second person (the "subject") places his hand so that the bottom of the cardboard hangs between his thumb and first finger, without touching either finger. The "observer" releases the cardboard without warning. The distance the cardboard falls before the "subject" pinches his fingers together to catch it can be used to determine the time it took the "subject" to react.

Make a Reaction-O-Meter from a piece of cardboard or very stiff paper. You will need to mark the Reaction-O-Meter with a set of lines which indicate the distance -- or time -- elapsed during the fall. Explain how the marks on the Reaction-O-Meter may be used to calculate the subject's reaction time; provide 2 examples. Describe your method, step-by-step, as if you were writing a manual for future physics students.

Use your device to measure the reaction times of at least five different people. Make at least 5 trials for each person. Calculate the mean reaction time for each person

                   sum of all trial times
           mean  = ----------------------
                     number of trials

and the standard deviation in each person's times:

                                           [                      ] 2
                                sum of all [trial time - mean time]
                                           [                      ]
  standard deviation =  sqrt ( ------------------------------------- )
                                   number of trials minus 1

Are there significant differences between the reaction times of different persons, or do all people have reaction times which are consistent with each other?

One common "bar bet" is to hold a dollar bill so that it hangs down vertically from one's fingers, with its bottom edge between the open fingers of a victim. The bet is that the victim won't be able to catch the dollar bill before it falls past his fingers. Based on your measurements, is this a fair bet?

Submit a report which includes the measurements of all trials, as well as the results. Include your Reaction-O-Meter with the report. You may also include interesting items you discovered during the course of the procedure.

This page maintained by Michael Richmond. Last modified Nov 18, 1999.