Controlled Experiment question?

Question

in a controlled experiment, why is it important to change just one variable parameter at a time? help!!

Answer 1

because if you change two or more variables at a time, you wouldn't know which was having an effect. By changing only one at a time you can be certain that the variable being changed is causing whatever observation you measure or detect

Answer 2

So you can tell exactly what the effect will be. If you change more than one, then how do you know which variable is responsible for the result?

Answer 3

Let's say you wanted to do an experiment with some cress seedlings. You might be interested in the effects of temperature on their germination and the effects of acid rain. So, you plant some cress seedlings and water them with acidic solutions of varying concentrations and you grow them at different temperatures. You could then measure (a) how long it took the seeds to germinate and (b) after germination the rate at which the seedlings grew.



When you had collected your data and came to discuss them how would you know whether what had happened to the seedlings was the result of the various acid concentrations or the different temperatures. You would not. In reality both would have had an affect on the seedlings but you cannot know if both had their own completely separate effects or if they were synergistic.



You must test only one variable at a time and keep everything else constant. Only then can you discuss with any confidence that the manipulated variable was the one that produced the measured effect.