This is an investigation that is usually considered too simple for GCSE so you will probably have done it before, lower down in the school. It is a very easy investigation to understand and carry out. Here we take a closer look at it and see how we would write it up to fulfil the marking criteria.
There is only one key variable and not much that needs to be controlled. Trying to produce an adequate theory to explain what happens using GCSE level scientific knowledge is also difficult. For this reason it would not normally be considered for the highest marks. There are lots of other similar investigations using pendulums or oscillating objects that could be carried out that would give access to the highest marks.
Pendulum Investigation writeup
Java based animation at NTNU JAVA Virtual Physics Laboratory
This is a very good demo. You can change the length, starting position, mass and even the gravitational force!