In a study of ball dynamics, students dropped a standard tennis ball inflated to a pressur… — ACT

In a study of ball dynamics, students dropped a standard tennis ball inflated to a pressure of $12\text{ psi}$ from heights of $1.0\text{ m}$ , $2.0\text{ m}$ , and $3.0\text{ m}$ onto a concrete floor. In each trial, the temperature was maintained at $21^\circ\text{C}$ , and the rebound height was recorded.

Suppose a student wants to conduct a follow-up experiment to determine how the internal air pressure of the tennis ball affects its rebound height. Which of the following procedures would be the most appropriate modification to the original study?

A
Drop a single tennis ball inflated to $12\text{ psi}$ from $2.0\text{ m}$ onto concrete, wood, and carpeted floors at $21^\circ\text{C}$ .
Drop tennis balls inflated to $8\text{ psi}$ , $12\text{ psi}$ , and $16\text{ psi}$ from a constant height of $2.0\text{ m}$ onto the concrete floor at $21^\circ\text{C}$ .Answer
C
Drop a tennis ball, a basketball, and a soccer ball, each inflated to a different pressure, from heights of $1.0\text{ m}$ , $2.0\text{ m}$ , and $3.0\text{ m}$ onto the concrete floor.
D
Drop tennis balls inflated to $8\text{ psi}$ , $12\text{ psi}$ , and $16\text{ psi}$ from $1.0\text{ m}$ , $2.0\text{ m}$ , and $3.0\text{ m}$ , respectively, onto different flooring surfaces.

Answer

The correct option is the procedure that drops tennis balls inflated to different pressures (

8\text{ psi}

12\text{ psi}

, and

16\text{ psi}

) from a constant height (

2.0\text{ m}

) onto the concrete floor at a constant temperature (

21^\circ\text{C}

To determine the effect of internal air pressure on the rebound height, the internal air pressure must be the only independent variable that is varied. All other potential variables—such as the drop height, landing surface, ball type, and temperature—must be kept constant. Dropping tennis balls with different pressures from a constant height onto the same concrete floor at the same temperature meets this requirement.

Step-by-Step Solution

Identify the target independent variable to be tested in the follow-up experiment.

The target independent variable is the internal air pressure of the tennis ball.

The student wants to determine the specific effect of internal air pressure on rebound height.

Determine the necessary control variables that must remain constant.

The drop height, landing surface material, ball type, and ambient temperature must be kept constant across all trials.

If multiple variables are changed, the experimenter cannot attribute the results to any single factor.

Evaluate the choices to find the one that isolates the target independent variable.

Varying only the tennis ball pressure (

8\text{ psi}

12\text{ psi}

, and

16\text{ psi}

) at a fixed height (

2.0\text{ m}

) on concrete at

21^\circ\text{C}

successfully isolates this variable.

This setup holds all other variables constant while systematically changing the pressure.

Key Concept

Isolating a single independent variable in a follow-up experiment

Estimated Time:1m 0s

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Step-by-Step Solution

Key Concept

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