Making Assumptions and relating them to both the model and the experiment
To be able to use the mechanics theory that I know, the following assumptions must be made, listed in order of importance.
* All motion is vertical – Although the horizontal motion could be taken into account, it cannot really be measured with the equipment we have, and since it isn’t wanted anyway it is best just to redo trials that result in some horizontal motion. This requires two further assumptions:
o There is no spin – spin causes the movement of the ball in other directions.
o The floor is perfectly horizontal – As it not being so would cause the ball to bounce in other directions (although in practise this can’t be helped anyway)
* There is no air resistance – As I cannot calculate air resistance using the theory I currently know, and the acceleration would no longer be constant. Since the ball is small, spherical and heavy, it should encounter little air resistance and be only lightly affected by it.
* The ball is uniform and perfectly spherical – The ball could appear to have different values of e because of having different densities or small deformations at different points on the surface, although the chance of these remaining unnoticed is minimal.
* Acceleration due to gravity is constantly 9.8ms-2 – Gravity must be constant so that the constant acceleration formulae can be used. Fortunately the gravity will deviate very little from this value so this assumption makes little difference.
Conducting the experiment
The experiment is set up by attaching two metre rules to a wall using a plumb line to ensure that they are vertical. For the first part of the experiment a ball was dropped from a number of heights, and the height it bounced back up to was recorded. For the second part the ball was dropped from different heights and the time taken for it to bounce three times was measured.
Any measurements in which the ball bounced at an angle of more than 10 degrees were ignored, as were any in which the ball hit the wall or when the person dropping the ball felt that they had accidentally given it some spin. In both parts results were taken for every 10cm between 1 and 2 metres, and 5 results were taken for each height. The heights that the ball bounced to were recorded by the height that the top of the ball reached, as this was easier to measure than the height that the bottom of the ball reached, so the results have been adjusted by 4.38cm, the diameter of the ball.