The Swinging Pendulum

Secondary School Science Teaching Methods

Adam Johnston & Sharon Ohlhorst


A simple pendulum consists of a mass hanging at the end of some massless (at least in theory) hanging device which is suspended from some pivot point.  In practice, this will be some washers hanging from a length of string.  The opposite end of the string is then suspended from a pen or pencil that is fixed to a table or desk.


Your task is to determine the dependence of the period of the swing (i.e.: the time it takes for the pendulum to swing to and fro) on the 1.) length of the string, and 2.)  mass of the washers.  In your possession are the following:


C  string

C  washers (all identical mass)

C  paper clips

C  tape

C  a stop watch


Note that you do not have any kind of length or mass measuring devices.  You will have to develop your own system for making these measurements.


Before you begin, you should discuss how you will go about conducting an experiment that shows the dependencies of period to mass and period to length.  Within your experiments, you should be careful to only change one variable at a time B otherwise, you cannot determine which change produced a certain result.  You should also discuss how to make your collected data most reliable.  Consider how accurate you are when timing one swing of the pendulum.  Could your accuracy be improved if you recorded more than one swing of the pendulum?


If time permits, you might also check the dependence of period to amplitude (the amount of swing to and fro).  When not analyzing this, you should be sure to keep the amplitude constant as much as possible.


To organize your information, you should eventually create data tables, and then show your data in the form of graphs.  Such graphs should probably show either length or mass on the horizontal axis, and period on the vertical axis.  (This follows the convention of showing the Aindependent variable@ on the horizontal axis and the Adependent variable@ on the vertical axis.