Original Project
Control of Variables
If more than one variable changes at the same time in an experiment, the outcome of the experiment may not be cl…
Item CR016003: To determine the effect of water temperature on getting stains out of shirts, it is important for all shirts to be washed for the same length of time because if they weren't, it wouldn't be possible to find out the effect of temperature.
To conserve energy, a college student wants to find out the lowest water temperature and the shortest length of time that is needed to wash his clothes and get them clean.
First he tests the effect of water temperature. He washes one shirt in hot water, one shirt in warm water, and one shirt in cold water. The shirts are identical and have identical stains. He uses the same detergent and washes the shirts for the same length of time.
Why is it important to wash the shirts for the same length of time?
- By washing the shirts for the same length of time the student can find out both the lowest temperature and the shortest length of time that is needed.
- By washing the shirts for the same length of time the student can find out the shortest length of time that is needed.
- If he does not wash the shirts for the same length of time the student cannot find the lowest water temperature that is needed.
- It is NOT important to wash each shirt for the same length of time because the student is not testing the length of time that is needed.
- Distribution of Responses
- Students Responding Correctly
| Group | Correct | Total | Percent |
|---|---|---|---|
| Overall | 1207 | 2502 | 48% |
| Grades | |||
| 6–8 | 622 | 1419 | 44% |
| 9–12 | 581 | 1074 | 54% |
| Gender | |||
| Male | 616 | 1230 | 50% |
| Female | 578 | 1233 | 47% |
| Primary Language | |||
| English | 1062 | 2145 | 50% |
| Other | 111 | 292 | 38% |