In a plant and light experiment, the amount of light can be the independent variable, plant growth can be the dependent variable, and the plant type, water amount, soil, and pot size should be controlled. In an exercise and heart rate experiment, exercise time or intensity can be changed while heart rate is measured. In a salt and ice experiment, the amount of salt can be changed while the ice melting time or temperature change is measured.
A strong experiment uses a clear chart to match each variable to its role before data collection begins.
Key Facts
- Independent variable = the factor you intentionally change in an experiment.
- Dependent variable = the outcome you measure or observe.
- Controlled variable = a factor kept the same so the test is fair.
- A fair test changes only one independent variable at a time.
- Change in measurement = final value - starting value.
- Average = sum of all measurements ÷ number of measurements.
Vocabulary
- Independent Variable
- The independent variable is the one factor the experimenter changes on purpose.
- Dependent Variable
- The dependent variable is the result that is measured to see how it responds.
- Controlled Variable
- A controlled variable is a factor kept constant so it does not affect the outcome.
- Fair Test
- A fair test is an experiment in which only the independent variable is changed while other important factors stay the same.
- Trial
- A trial is one repeated run of an experiment used to make results more reliable.
Common Mistakes to Avoid
- Changing more than one independent variable at once is wrong because you cannot tell which change caused the result.
- Calling the measured result the independent variable is wrong because the measured result is the dependent variable.
- Forgetting controlled variables is wrong because outside factors like temperature, time, or materials can change the results.
- Using only one trial is weak because random errors can make one result misleading.
Practice Questions
- 1 A student tests how light affects bean plant growth. Plants get 2 hours, 6 hours, or 10 hours of light each day, and their heights after 14 days are 5 cm, 12 cm, and 18 cm. Identify the independent variable, dependent variable, and two controlled variables.
- 2 A student measures heart rate after exercising for 0, 2, 4, and 6 minutes. The heart rates are 80, 104, 128, and 150 beats per minute. What is the change in heart rate from 0 minutes to 6 minutes, and what is the independent variable?
- 3 A student wants to test whether salt makes ice melt faster. Explain which variable should be changed, which result should be measured, and why the amount of ice and room temperature should stay the same.