A fair test: which paper towel soaks up most?
Dip paper towels and a cloth in water and measure how much each soaks up. First see how an unfair test can fool you, then make it fair by changing only one thing at a time.
Core concept
In short: Learn to test fairly: change one thing, keep everything else the same.
In a fair test we change only one thing (the variable we are testing) and keep everything else the same, so we know what caused the difference
Topic: Scientific learning
Scientists find things out by asking a question, testing it and measuring the results. Our question: which towel soaks up the most water, a thin paper towel, a thick paper towel or a cotton cloth? To find out, we dip a sheet of each in water, squeeze it out into a measuring cylinder and read how many millilitres (mL) it held. But many things can change the result: the towel, the size of the sheet and how long it stays in the water. These are called variable: Something that can change in an experiment. Change one, measure another, and keep the rest the same. All key words. If we change more than one of them at once, we cannot tell which one made the difference. A fair test: A test where you change only one thing, so you know what caused the result. All key words changes only the variable we are testing and keeps all the others the same.
What you will learn
- Name the variables in an experiment.
- Explain why changing two variables at once makes a test unfair.
- Plan and carry out a fair test, changing one variable at a time.
- Use measurements to answer a scientific question.
Before you start
- Read a scale in millilitres (mL).
Materials
- Thin paper towels, thick paper towels, a cotton cloth, scissors, a bowl of water
Equipment
- A 30 mL measuring cylinder, a stopwatch, a ruler
Procedure
- Test a big thin towel and a small thick towel, and record both.
- Test all three towels with small sheets for 30 seconds each, and record each.
- Test the thick towel for 10 seconds and for 60 seconds, keeping the size the same, and record both.
How this simulation is simplified
- A small sheet is 10 cm × 10 cm and a big sheet 20 cm × 20 cm, four times its area.
- A small sheet soaked full holds 4 mL (thin towel), 7 mL (thick towel) or 5 mL (cotton cloth).
- Sheets fill half in 10 seconds, nearly (90%) in 30 seconds and completely in 60 seconds, and all the water is squeezed out.