How steady is a pendulum?

A pendulum is a clever timing device that was once used to help clocks keep time. If you were making a clock, you would need to know all about pendulums.

Does the time for a swing depend upon the size of the swing? How does the pendulum change its speed while it is swinging?

You can begin to answer these questions using a sensor connected to the computer.

One complete swing of a pendulum - there and back - is called a period. The size of a swing is called the amplitude.

Setting up

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	Set up your apparatus as shown above.
	Connect a Position or Angle sensor to the interface. Connect the interface to the computer.
	Get the computer ready to measure the position of the arm over 10 to 30 seconds.
	Start the computer recording and the pendulum moving.
	Adjust the sensor to get the computer to read zero when the pendulum is at rest.
	Try to fit the graph from a large swing on the screen. If you can, set the y axis so that you measure from say, -100 to +100 units.
	Get the computer to start recording only when you start to move the pendulum.
	Try to get the computer to let you keep two or more sets of swings on the screen.

Make a plan

Your task is to find out if the size of the swing affects the time for a swing. You will need to record several swings - some large and some small. Decide whether you will start with a large swing and then try smaller ones - or whether you will start with a small swing and then try larger ones.

Questions

Looking at your graph, how can you tell that the pendulum is at the mid-point of its swing?
With your graph on the screen, use the computer to read off the time for large and small swings. You'll need to find the difference between points along the time axis.
Is there a simple pattern in the results? Why then are pendulums used in clocks?

Extra

How does the mass of the pendulum bob affect the period of a swing? Do an experiment where you measure the periods of large, medium and small pendulum bobs.