# Compound pendulum question

1. Apr 12, 2016

### Motorbiker

• Thread moved from the technical forums, so no HH Template is shown.
I am doing the compound pendulum experiment but I am stuck on how to find the value of g from the graph

Here's a description of the compound pendulum:

The compound pendulum AB is suspended by passing a knife edge through the first hole. The pendulum is pulled aside through a small angle and released, whereupon it oscillates in a vertical plane with a small amplitude. The time for 10 oscillations is measured. From this the period T of oscillation of the pendulum is determined.

The method to find the acceleration due to gravity, is not really making much sense.

A graph is drawn with the distance d of the various holes a straight line is drawn parallel to the X- axis from a given period T on the Y- axis, cutting the graph at four points A, B, C, D. The distances AC and BD, determined from the graph, are equal to the corresponding length l. The average length l = (AC+BD)/2. In a similar way , l/T2 is calculated for different periods by drawing lines parallel to the X-axis from the corresponding values of T along the Y- axis. l/T2 should be constant over all periods T, so the average over all suspension points is taken. the acceleration due to gravity is calculated from the equation g= 4π2(l/T2).

I don't know what the given period is, do you just use any random period? For I/T2, do you just like draw vertical lines parallel to all the values of T and then average the T values?

2. Apr 12, 2016

### Staff: Mentor

This would so be so much easier to understand with a sketch of the setup and a picture of the graph.

3. Apr 12, 2016

### Motorbiker

I won't be able to upload a sketch of the setup since my printer isn't working at the moment.

Is it okay if I show you an accurate picture of the experiment and a picture of the graph?

4. Apr 12, 2016

### Staff: Mentor

That's a good start!