A student is conducting an experiment using a ball that is attached to the end of a string on a pendulum. The student pulls the ball back so that it is at an angle to its resting position. As the student releases the ball, it swings forward and backward. The student measures the time it takes the ball to make one complete period. A period is defined as the time it takes the ball to swing forward and back again to its starting position. This is repeated using different string lengths.What would be an appropriate control variable for this experiment?

The Praxis General Science: Content Knowledge (5435) exam is a test required by many states for credential candidates planning to teach science at a high school level. It is a single, computer-delivered test that includes questions from five content domains.

The exam content categories are Scientific Methodology, Techniques, and History; Physical Science; Life Science; Earth and Space Science; and Science, Technology, and Society.