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 Suggested Teaching Activities

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 a PC.

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

Setting up

Set up your apparatus as shown above.

 1 Connect a position or angle sensor to the interface. Connect the interface to the computer. 2 Get the computer ready to measure the position of the pendulum arm over 10 to 30 seconds. 3 Start the computer recording and the pendulum swinging. 4 Adjust the sensor to reset the computer to read zero when the pendulum is at rest. 5 Start recording on the computer only when you start to move the pendulum. 6 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 larger ones.

Questions

 1 Study the graph. How can you tell that the pendulum is at the mid-point of its swing? 2 With your graph on the screen, use the computer to read off the time for large and small swings. 3 Is there a simple pattern in the results? Why then are pendulums used in clocks? 4 Choose one of the peaks on the graph. Use the computer to read off the gradient at the different points shown in the diagram. Print the graph and label the points where: the pendulum speed is highest the pendulum speed is lowest the pendulum speed is increasing the pendulum speed is decreasing

Extensions
How does the mass of the ball affect the period of a swing? Do an experiment where you measure the periods of large, medium and small balls.

 Mechanics Distance and Time How steady is a pendulum? Impulse and Momentum

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