A typical pendulum will be set up as shown:

As clearly seen in this diagram, the length  of a pendulum, L, should be measured to the centre of the bob (to its centre-of-gravity).

 

1. Clamping of Split Cork or Bung

This diagram shows the correct use of a clamp to hold a split cork (or split rubber bung in this case). Note how the ruler can be placed against it to measure the length of the string.

 

As can be seen from this image, if the split cork is clamped higher up it is difficult or impossible to measure the length of the pendulum accurately.

 

This diagram shows the correct way to clamp the split cork. When the jaws of the clap compress they will hold the string firmly between the two halves.

Incorrect alignment of the cork. Here tightening the clamp will not result in the sting being held more firmly.

 

2. Measuring Pendulum Length

When measuring the length of the pendulum we must measure to the centre of the pendulum bob.

 In this case the length of the pendulum would be recorded as 56.7 cm (half way between 55.7 cm and 57.7 cm)

 

Correct position to read the length of the pendulum – placing the eye at the level of the bob to avoid parallax error.

 

 

3. Positioning of Stand

The top picture shows the stand being used correctly. In the lower diagram the bob will not be able to extend beyond the edge of the table.

 

Practical Skills