Testing materials fairly
Chemistry · Key Stage 2 · The School
One thing changes, everything else stays
A test is FAIR when you change only the thing you are testing and hold everything else still. To find which paper towel soaks up most water you must use the same amount of water, the same size piece of towel, the same time, and the same way of measuring. Change two things at once and you cannot tell which one caused the result.
Measuring the same way every time
Guesses are not evidence. Use standard units — millilitres, centimetres, seconds — and the same equipment each time. Read a measuring cylinder at eye level. Write results down as you go, in a table you drew before you started, rather than trying to remember them. Then repeat: doing it three times shows whether the result holds.
What the results do and do not show
A conclusion says what the results support, and no more. If towel A held more water than towel B in your test, that is what you found — it does not follow that A is the best towel for every job or worth the price. Say what you measured, what happened, and what you would test next. Noticing a result you did not expect is a finding, not a failure.
Question: which material keeps a drink warmest? Write the plan first. CHANGE: the wrapping (foil, bubble wrap, wool, nothing). MEASURE: temperature after 20 minutes. KEEP THE SAME: same cup, same starting temperature, same amount of water, same room, same thermometer. Now draw the results table BEFORE you boil anything — deciding what to write down is what forces you to notice the controls.