Science in Punggol study guide · Article 0003 of 20

A fair test changes one relevant factor and measures its effect while keeping other important conditions the same. This makes it easier to decide whether the changed factor explains a difference in the results.

If two toy cars travel different distances but start at different heights, we cannot tell which difference caused the outcome. The investigation needs a clearer comparison.

On this page: Name what you change and measure · Keep other relevant conditions the same · Choose controls that answer the question · Worked question

Name what you change and measure

The changed variable is the factor deliberately varied. The measured variable is the outcome recorded. In a test of how a surface affects a toy car’s travel distance, the changed variable is the surface and the measured variable is distance travelled.

Name the measured outcome precisely. “The car” is too vague. “The distance travelled after the car reaches the test surface” tells us what to record and where measurement begins.

The investigation question determines the variables. A test about surface type is different from a test about ramp height, even if both use a car and ramp. Equipment alone does not define the question.

Keep other relevant conditions the same

For the surface test, use the same car, ramp and release point. Release the car without an extra push. Put each test surface in the same position and measure from the same reference point.

These controls reduce other possible explanations for the results. A stronger push or higher starting point could change travel distance, even if the surface stayed the same.

Keeping conditions the same does not mean making both setups identical. The intended changed variable must differ. If both surfaces are the same, the investigation no longer compares their effects.

Some conditions are difficult to control. Wind or rain may change during an outdoor test. A stable indoor space may make a small home comparison easier. Record conditions that could still affect the outcome.

Choose controls that answer the question

List conditions that could affect the measured result. Keeping the observer’s shirt colour unchanged is unlikely to help a toy-car test. Keeping the car and release point unchanged is relevant.

Different questions need different controls. Water, light, plant type and time may matter in a plant investigation. The car, starting position and surface conditions may matter in a movement investigation. Avoid using one memorised list for every experiment.

Measurement must also be consistent. Comparing one car’s stopping distance with another car’s distance after two seconds uses different rules. The numbers would not describe the same outcome.

Repeated trials can check consistency, but they cannot repair an unfair design. If several relevant factors change in every trial, their separate effects remain unclear.