Simple Experiments

In science, the term "simple experiment" has a specific meaning. To understand the differences between a simple experiment and a more complicated, controlled experiment, consider this example. Suppose that you are watching a candle flame and ask yourself, "Would the color of the flame be different if I added salt to the pool of melted wax at the base of the flame?" If you do this to only one candle, it is called a simple experiment. You can make it a better experiment, a controlled experiment, by using two candles of the same type. You light both, then add salt to the wax of one but not to the other.

After you have made your experimental change, you can now compare the two candles side by side. In the next chapter you will see how and why such controlled experiments can be much better science than simple experiments.

Experimental Terms

There are some special terms that will help us talk about different kinds of experiments:

• Experimenter   (that's you)
• Independent variable   The thing you are changing, in this case the salt you are adding to the wax of one candle. You, as the experimenter, make this change.
• Dependent variable   The effect of the change, in this case how the color of the flame changed after you put the salt in the wax of one candle. This change depends upon the independent variable.
• Result   Your observation of the change. In this case, what you observed about the change in color of the flame

If the flame does change color when you add the salt to the wax, we say that the independent variable and the dependent variable are related variables.

As an experimenter, you must try not to let other things change beside your two main variables. Let's say that you want to learn whether adding baking soda to the water used for watering bean plants will make them grow better. You must decide how much baking soda to put in the water and carefully observe the growth of the plants before and after giving them this water. Obviously, you must not make any other changes, such as adding more water, using different temperatures, or using a different amount of light. These variables would confound the results; you would not be able to judge which of the four variables—baking soda, or more water, or different light, or different temperature—might be related to any difference in growth. So you try to keep other possible variables constant, or the same, during the experiment. You try to keep all possible variables constant except the one you built into your experiment—adding the baking soda to the water as your independent variable.