Which statement is true for an object at terminal velocity falling through a fluid?

Which statement is true for an object at terminal velocity falling through a fluid?

• A. Drag is zero and weight accelerates the object
• B. Weight greatly exceeds drag and the object continues to accelerate downward
• C. Drag equals weight; net force zero; acceleration zero
• D. Drag dominates and the object accelerates upward

Answer: (D)

When an object falls through a fluid and reaches terminal velocity, the air (or fluid) drag increases with speed until it exactly balances the weight pulling the object downward. With the upward drag equal in magnitude to the downward weight, the total force on the object is zero, so there’s no further acceleration and the velocity stays constant. This is why the other scenarios don’t describe terminal velocity: if drag were zero, gravity would keep speeding the object up; if weight exceeded drag, the object would continue to accelerate downward; and claiming drag dominates to push the object upward would imply a reverse motion not characteristic of the steady-state downward descent at terminal velocity. The key idea is balance of forces: drag equals weight, net force is zero, and acceleration is zero.

When an object falls through a fluid and reaches terminal velocity, the air (or fluid) drag increases with speed until it exactly balances the weight pulling the object downward. With the upward drag equal in magnitude to the downward weight, the total force on the object is zero, so there’s no further acceleration and the velocity stays constant.

This is why the other scenarios don’t describe terminal velocity: if drag were zero, gravity would keep speeding the object up; if weight exceeded drag, the object would continue to accelerate downward; and claiming drag dominates to push the object upward would imply a reverse motion not characteristic of the steady-state downward descent at terminal velocity. The key idea is balance of forces: drag equals weight, net force is zero, and acceleration is zero.