When a pendulum swings through a small angle (about 7° or less) the time taken for one swing i.e. the periodic time, is given by the formula:

T = 2pi*sqrt(L/g) where L is the length of the pendulum and g is the acceleration due to gravity.

- Press the Get Ruler button.
- Measure and record the length of the pendulum.
- Press the Start Swing button.
- At a suitable position of the bob (eg left hand side), press Start Clock.
- After 20 swings press the Stop Swing button. This will also stop the clock. Record the time for the 20 swings.
- Press the Reduce Length button. The length is reduced by some random amount.
- Repeat steps 1 to 6 at least six times.
- Reset if necessary to get sufficient readings

**Results:**

Record the results in a table with headings as indicated here:

Length of pendulum(m) | Time for 20 swings(s) | Time (T) for 1 swing | T^{2}

**Graph:**

Plot a graph (on graph paper) of L (y-axis) against T². Note: Start both axes at zero. A straight line graph through the origin shows that length is proportional to periodic time squared. Note: The slope of the line is L / T²

**Calculations:**

From the graph, pick two suitable points (far apart) to calculate the slope of the line. The value of g is calculated using the formula: g = 4(pi)²(slope)

- Ensure that your eye is level with the centre of the bob when measuring length to avoid parallax error
- Use a split cork to hold the string (keeps length constant and is easy to measure from bottom of cork to centre of bob)
- Do not cause the pendulum to swing through an angle greater than 7 degrees approx.
- Ensure that the pendulum swings in one plane only - avoid circular movements
- Use a long pendulum as much as possible to keep measurement errors (length and time) relatively small