“I think we should try three different numbers of drops so we have enough data to look for patterns,” said Jessie. “We should start with numbers of drops that have a pattern like 1, 2, and 4 drops. Then it will be easier to see how changing the number of drops changes the area of the spots. We should also do three trials as we did in Distance vs. Time. Then if the areas of the spots for all three trials are close, we will know we didn't make any big mistakes.”
Identifying Variables
“As you were talking, you identified the two main variables in your experiment,” said Mr. Moreno. “The variables are number of drops (N) and area (A). The two main variables in an experiment have special names. The variable with values we know in the beginning of the experiment is called the manipulated variable. We often choose the values of the manipulated variable before collecting the data.”
Arti and Jessie chose 1 drop, 2 drops, and 4 drops as the values for the number of drops so that the spots they made would not be too big. They made three spots of water with 1 drop, three spots of water with 2 drops, and three spots with 4 drops of water on paper towels.
“The variable with values we learn by doing the experiment is called the responding variable,” said Mr. Moreno. “Your responding variable is the area of the spots. The area of each spot changes depending upon the number of drops of water you use.”
Mr. Moreno added, “There are other variables that can affect the size of the spots. For example, if we use a bigger eyedropper or a different liquid, the size of the spots might be different. These other variables should stay the same during the whole experiment so that the only thing that affects the area of the spots is the number of drops. The other variables that stay the same are called fixed variables.”
When the spots had dried a little, Arti and Jessie traced around each spot with a pencil and used scissors to cut out each spot. Then they measured the area of each spot and recorded it in a data table.
