How do you control other variables in an experiment?

In one line

The rule

Controlled variables are all the factors in an experiment that are kept constant to ensure that only the independent variable affects the outcome. (NCERT, Class 6/8)

Let's understand it simply

Imagine you want to find out if a new cricket bat helps you hit the ball farther. If you use different balls, play on different grounds, or have different bowlers, you won’t know if the bat made the difference. So, you keep everything else the same: same ball, same ground, same bowler. Only the bat changes. This way, you know any change in how far the ball goes is because of the bat, not something else.

How it works

1. List all possible variables: Think about everything that could affect your result (like sunlight, water, soil in a plant experiment).
2. Pick your independent variable: Decide what you want to change (for example, amount of sunlight).
3. Identify controlled variables: These are all the other things that could affect your result (like water, soil type, pot size).
4. Keep controlled variables constant: Make sure these do not change for any group in your experiment. For example, give all plants the same amount of water, use the same soil, and same type of pot.
5. Check regularly: Keep checking that these variables stay the same throughout the experiment.

The story behind it

Scientists started controlling variables to make sure their results were fair and could be trusted. If they did not, others could not repeat their experiments and get the same results. This idea became a key part of the scientific method, which is used all over the world today.

Where you see it in real life

• Cooking: When testing a new recipe, you keep the amount of salt, oil, and cooking time the same, and only change one ingredient.
• Cricket practice: To test a new bat, you use the same ball, same bowler, and same pitch for all tries.
• Growing plants: In a school experiment, you give all plants the same water, soil, and pot, but change only the sunlight.
• Pressure cooker: To test if a new lid cooks faster, you use the same amount of dal, water, and flame.

Why it matters

• Fair results: Controlling variables makes sure your results are because of what you changed, not something else.
• Repeatable experiments: Others can do the same experiment and get the same result.
• Better science: It helps scientists trust each other's work and build new ideas.
• Used in exams: Questions about experiments often ask you to name controlled variables.

Common mistakes

• Forgetting a variable: Sometimes, students forget to control something important, like water in a plant experiment.
• Changing more than one thing: If you change more than one variable, you cannot tell which one caused the result.
• Not checking during the experiment: Sometimes, a variable changes by mistake (like someone adds extra water to one plant).

Remember it

Keep everything the same except what you are testing. Only one change at a time!