Is that a fair test of whether fertilizer makes a plant grow to be larger? No! We changed two things (type of soil and fertilizer) so we have no idea whether the plants with fertilizer grew to be larger because of the fertilizer or whether the other plants were stunted by being grown in sand. The plants with soil and fertilizer grow to be much larger than the ones grown in sand without fertilizer. We put all six pots in the same location and water each one with the same amount of water every other day. But, we run out of soil so we put the seeds without fertilizer in three pots filled with sand. We put seeds of the same kind in three pots with fertilizer and rich soil. Let's pretend we're doing an experiment to see if fertilizer makes a plant grow to be larger than a plant that doesn't receive fertilizer. That's not a fair test! The only thing that should change between the two tests is the car we should start them down the ramp in exactly the same way. If we gently release the first car, but give the second car a push start, did we do a fair test of which car was fastest? No! We gave the second car an unfair advantage by pushing it to start.
You conduct a fair test by making sure that you change one factor at a time while keeping all other conditions the same.įor example, let's imagine that we want to measure which is the fastest toy car to coast down a sloping ramp. It is important for an experiment to be a fair test.
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