Asking a testable question
Chemistry · Key Stage 1 · The School
What makes a question testable
A testable question has an answer you can measure. "Which material stretches furthest?" is testable — you measure with a ruler. "Which material is prettiest?" is not testable. Nobody can measure pretty. Science only asks questions with a measurable answer.
Turning a vague question testable
Start vague: "Which bag is best?" Ask what "best" actually means here. Do you mean strongest? Lightest? Cheapest? Pick one meaning and the question becomes testable. "Which bag holds the most weight before it tears?" can now be measured.
Predicting before you test
Before testing, make a prediction. Say which material you THINK will win, and why. A prediction is a guess based on what you already know. Being wrong is fine. Testing exists to find out whether the prediction was right. Wrong predictions still teach something.
A report published by the Environment Agency describes a real bag test from 2008. Here is a question it can answer. Start vague: "Which bag is best?" Make it testable. Which holds more weight before it gives way? A thin plastic bag or a thick bag for life? A bag for life is made to be used again. Predict: the thick bag will hold more, because it feels stronger. A machine moved each bag up and down, like walking. The test began with 5 kilograms, about as heavy as 5 litres of water. After 4 minutes, 1 more kilogram went in each minute. This went on until the bag gave way. On average, thin bags held a little over 18 kilograms. Thick bags held 19 kilograms. That is less than 1 kilogram more. The report calls the difference slight. The prediction was right, but only just.
Why this step comes first
Testing without a clear question wastes time. You might collect numbers and still not know what they answer. Asking a testable question first tells you exactly what to measure and why. It is the first real step of any science test.