In section one, you learned that in an experimental investigation there should only be one independent variable. Kaitlin had too many independent variables in her experiment. What should she have done with all the other variables such as amount of water, size of cup, number of beans, and amount of soil? She should have made them constants. In other words, she should have kept all of these the same throughout the experiment.
Look at the table below. It shows what Kaitlin did in her experiment in the first column and what she should have done to create a “fair test” experiment in the second column.
| Kaitlin's Experimental Design | "Fair Test" Experimental Design |
| 3 different size cups (3 ounce, 10 ounce, and 16 ounce) | Same size cup (10 ounce) |
| Different amounts of soil. (She filled the different size cups up to the top. Since they were different sizes they each held different amounts.) | Same amount of soil (225 mL of soil) |
| Number of beans (1 bean, 8 beans, and 6 beans) | Same number of beans (6 beans in each cup) |
| Amount of water (3 mL, 10 mL, and 16 mL) | Same amount of water (16 mL) |
A chart like the one below is a helpful tool when trying to organize the parts of an experimental investigation. See if you can complete the chart below to help Kaitlin redesign her experiment.
