In Science-based investigations you usually start with a question. I try to simplify it by asking ‘What is the effect of x on y?’. X and y represent two variables you will investigate.
X is the Independent variable. This is the variable the scientist needs to be in control of, manipulating the conditions to suit the situation. In the simplest set up one condition is changed and the effect is measured in a set time, or over a period of time. In more complex experiments more than one condition can be set in order to compare the results.
Y is the Dependent variable. This is the variable the scientist will measure. The scientist cannot decide what the result will be, but must observe and record. It is important that the correct apparatus must be used and that accurate measurements must be taken. For added accuracy it is advised to take more than three measurements and to calculate an average.
Once you know what you want to investigate you need to make an educated guess about the possible outcome of the experiment. This is known as your hypothesis. A hypothesis is a prediction written in the future tense. It should take into account the cause and effect principle. If I change a condition, what effect will it have on the results.
Next you need to look at the variables that must remain the same in all your experimental set ups. These are known as the Fixed/Controlled variables. To make it easier to determine what they are I have divided them into Apparatus, Organisms and Environment.
In the experiment in the infographic we ask: What is the effect of the presence of leaves on the Oxygen content of the air? X is the presence or absence of leaves and y is the oxygen. In this case we measure the oxygen dissolved in water using a methylene blue indicator. The fixed variables include: Apparatus: same size and type measuring cylinders, same size and type rubber stoppers. Organism: same type of plant. Environment : Temperature of incubation, time of incubation, indicator used (volume and type).
If you follow these basic Planning steps your experiment will be a success…Good luck with the Science Fair!