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.
Imagine a class tests which wrapping keeps a drink warmest. The plan comes first. CHANGE: the wrapping (foil, bubble wrap, wool, nothing). MEASURE: temperature after 20 minutes. KEEP THE SAME: same cup, same amount of water, same room, same thermometer, and the same starting temperature, 50°C. They draw the results table BEFORE any water is poured, and an adult pours and supervises the hot water. The readings below are made up to show the steps. After 20 minutes the cups read: nothing 34°C, foil 33°C, bubble wrap 38°C, wool 41°C. Now work out the drop for each cup: start minus end. Nothing dropped 16°C, foil 17°C, bubble wrap 12°C, wool 9°C. Wool has the smallest drop, 7°C less than nothing, so it lost the least heat. The class would repeat every cup three times. Repeats of one wrapping may differ by about 1°C. So a 1°C gap means nothing. The 7°C gap for wool would still stand out. Their conclusion: in this test, wool kept the water warmest. It does not say wool is best for every job.