An experiment is easier to interpret when it isolates the factor you want to investigate. The independent variable is what you deliberately change; the dependent variable is what you measure. Other relevant conditions should be controlled or recorded. Suppose you compare how quickly sugar dissolves in water at different temperatures. Keep the water volume, sugar amount, container type, and stirring method consistent. Decide in advance what counts as “dissolved.” Repeat the comparison because measurements and conditions vary. Changing several factors at once makes it difficult to identify the cause of a difference. Even a careful test has limitations, so describe them. A result that disagrees with your prediction is information, not a reason to discard the observation. Use only safe materials and comfortable water temperatures. Practice: Write a testable question about a harmless everyday process. Identify the changed factor, measurement, controlled conditions, and one source of uncertainty.