Designing an experiment and taking measurements

The experimental protocol

A protocol is a precise list of the steps to be followed in order to test a hypothesis. It must be detailed enough to enable another person to repeat the experiment exactly and obtain comparable results.

Vary only one parameter

For the experiment to be reliable, only one factor at a time (the parameter being tested) should be varied, whilst keeping all others constant. These are referred to as the variable factor and the fixed factors.

Choosing the right instruments

Each physical quantity is measured using a suitable instrument.

Quantity	Instrument	Unit
Length	Ruler, metre	m (metre)
Mass	Balance	kg
Temperature	Thermometer	°C
Time	Stopwatch	s

Repeating the measurements

A single measurement may contain an error. It is advisable to repeat the experiment several times and calculate an average, for example (m1 + m2 + m3) / 3, to obtain a more reliable result.

Common pitfall

Failing to keep the other parameters constant completely distorts the results: it then becomes impossible to determine which factor is actually responsible for the observed effect.