The minimum acceptable would be 5 sets of results. Unless the procedure is particularly time consuming more would be expected.
Don't forget you must measure and record the value of all the control variables as well. Some will only need to be measured once if they can't change. Others, such as temperature, may need to be measured at the start and end of an experiment to show they haven't changed by much, if at all.
There must be some sort of sensible order or pattern to the results you have decided to take. e.g. use values from 10.0 to 100.0 cm in steps of 10.0 cm.
Always try to be as accurate as possible. Take as much time and care as is necessary to get good results. It is better to have fewer results which are very accurate than lots of rushed inaccurate results.
Always repeat observations and measurements.
Double check each measurement as you take it to reduce human error. Repeat the whole experiment at least twice, three times if you can.
Observations must be detailed and written clearly and precisely using scientific words.
Measurements must be organised logically in tables.
Tables must;
All numbers must be recorded to the accuracy you measured them to,
including trailing zeroes.
e.g. if you are measuring length with a ruler you can measure to the nearest
millimetre.
60mm or 6.0cm or .060m are all correct, but
60.0mm, 6cm or .06m all show the wrong accuracy.
Have a look at the table below as an example of how to lay out a table. All the results have been made up. Note that the distances are not exactly 10.0 cm apart as they were planned to be. In many experiments it can be too fiddly and time consuming to get the values exactly right. This does not matter but it is important to record the actual value.
angle of slope = 40°
mass of trolley = 1014g
| distance (cm) |
speed (m/s) | average speed (m/s) |
||
|---|---|---|---|---|
| 1st | 2nd | 3rd | ||
| 10.1 | 1.1 | 1.1 | 1.2 | 1.13 |
| 20.3 | 1.5 | 1.7 | 1.6 | 1.60 |
| 29.7 | 1.9 | 2.0 | 1.9 | 1.93 |
| 40.0 | 2.2 | 2.4 | 2.2 | 2.27 |
| 50.2 | 2.5 | 2.5 | 2.5 | 2.50 |
| 59.8 | 2.8 | 2.8 | 2.6 | 2.73 |
| 70.4 | 3.1 | 3.0 | 2.9 | 3.00 |
| 80.1 | 3.1 | 3.2 | 3.2 | 3.17 |
| 91.0 | 3.2 | 3.5 | 3.3 | 3.33 |
| 99.6 | 3.5 | 3.5 | 3.7 | 3.57 |