1.4 Variables: What You Change vs What You Measure

Here is the single most useful idea in this chapter. In any experiment there are things you can change, and things you can observe to see whether your change made a difference. Scientists call these variables.

Go back to the puri. What could we change?

• the thickness of the rolled dough,
• the size (diameter) of the circle,
• the type of flour (atta, maida, …),
• the temperature of the oil,
• the way we slide the dough in (flat? at an angle? slowly?).

And what could we observe or measure to judge the result?

• Did it puff? — a yes/no observation,
• How long did it take to puff? — a number, in seconds,
• Is one side still thinner than the other? — yes/no,
• did the oil splatter, smell, or smoke?

Two Kinds of Variable The thing you deliberately change is the independent variable (the cause you are testing). The thing you measure to see the effect is the dependent variable (it depends on what you changed). Everything else you deliberately keep the same so it cannot mislead you — these are the controlled variables.

Use the sorter below to practise telling them apart. For the question “Does hotter oil make a puri puff faster?”, decide whether each item is something you change, something you measure, or something you should keep the same.

Change it, measure it, or keep it the same?

Click a card to cycle it through the three bins. Then press Check.