Experimental Design

• In any experiment, only the independent variableThe variable that is deliberately changed by the experimenter. should be changed. All other variables must be controlled.
• The dependent variableThe variable that is measured as the outcome of the experiment. is measured to see how it responds to changes in the independent variable.
• If control variablesVariables that must be kept constant to ensure a fair test. are not kept constant, the results will be invalid because you cannot tell what caused any changes observed.

Planning an Investigation

• Preliminary research should be conducted before the main experiment to understand the theory, choose appropriate apparatus, and identify variables.
• Preliminary studies are small-scale trial runs that help identify additional variables, find the best way to control them, and refine the method.
• The choice of apparatus and techniques should be based on the underlying physics of the investigation.
• A hypothesisA testable prediction about the relationship between variables, based on theory or prior knowledge. should be formed from preliminary research and tested by the experiment.

Investigative Approaches

• Use a wide range of equipment confidently, including traditional apparatus and ICT tools such as data loggers.
• Execute experimental steps in the correct sequence -- missing or reordering steps can invalidate results.
• Fine-tune your technique: adjust apparatus or method to obtain a suitable range of readings.
• Consider external influences that could affect results, such as room temperature fluctuations, air currents, or electromagnetic interference.
• Monitor changing conditions by measuring variables that might change during the experiment (e.g. record room temperature at start and end).