Skill Guide : P
Planning Table Example - Simple pendulum
Aim
To investigate how the length of a simple pendulum affects the time for one complete swing.
One complete swing is, for example;
b - c - b - a -b
For this experiment there is only one key factor,the length of the pendulum.
Planning table (condensed)
This doesn't take much time to write out, but anyone looking at it can easily see at a glance that you know what you are doing and have planned a fair test. You would need to have carried out some trial experiments, and thought about how a pendulum works, before being able to make a summary such as this.
| variable | value or range | how measured | |
|---|---|---|---|
| time | find out | for 20 swings | stopwatch |
| length | preset to | 20, 40, 60, ...160cm; 3 repeats | ruler |
| size of swing | same | No effect. about 10 degrees | protractor |
| mass | same | No effect. About 20-50g | electronic balance |
| air resistance | same | very small | |
| gravity | same | can't change. 10 N/kg. | |
Planning table (full)
| variable | value or range | how measured |
|---|---|---|
| Dependent variable (continuous): Time | ||
| Time for one complete swing | measured: The time for 20 swings will be measured. typical values: At most a few seconds per swing |
digital stopwatch records to .01s |
| Independent variable (continuous): Length | ||
| length of string | range: 20cm to 160cm, in steps of 20cm, number of results: 8 repeats: 3 repeats at each length. |
metre ruler accurate to 1mm |
| Control variables | ||
| size of swing | This will be kept small (about 10 degrees). The size of the swing does not have much effect on the time of swing. | protractor |
| mass of pendulum bob | Has no effect on the time of swing, so the mass used is not
very important, although the size will affect the air resistance. Value will be about 20-50g |
electronic balance |
| air resistance | A small, dense, metal bob will be used to minimise air resistance. | |
| pull of gravity | This will stay the same. The pull of gravity gets less as you
move away from the centre of the Earth, so would be slightly less
at the top of a mountain. Gravitational field strength at the surface of the Earth is about 10 N/kg. |
|
NOTE: An investigation such as this would be too simple to give access to high marks.