How to set up the pendulum experiment

 Tie a small object onto the bottom of the string. It has be heavy enough to make the string go tight. I used a rubber but you could try a small stone or a lump of Blu-Tack.

 Use a ruler and a pen. Measure from the MIDDLE of the object that you tied on. Put a mark at 20cm from the middle of the object, then 25cm, then 30cm, then 35cm etc.

Next hang your pendulum at the 20cm mark. Try to get it so that it doesn't catch too much as it swings. Pull it a couple of cm to one side (10 or 20 degrees - as shown in the photo) and let go.

One whole swing is across AND back, called the TIME PERIOD T. But you are going to time 10 whole swings. We'll call that 10T. The reason we do that is because T is very small and too close to your reaction time. Doing 10T means that there is less RANDOM ERROR in the experiment.