Physics 211, Extra Credit for Week #2: due Mar 22, 1999

What is the average reaction time of a human being?

This project must be done by individuals.

Read Chapter 2, problem 42. It shows how one can use a piece of cardboard to measure human reaction times. One person holds the cardboard so that it hangs down between the fingers of a second person. The first person releases the cardboard without warning. The distance the cardboard falls before the second person pinches his fingers together to catch it can be used to determine the time it took the second person to react.

Make a Reaction-O-Meter from a piece of cardboard or very stiff paper. Figure out a way to use it which will yield consistent measurements. 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:

                                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 Mar 2, 1999.