You are out for a bicycle ride on a calm, windless day. You are heading northward on a level road and are experiencing a pressure drag force that pushes you toward the south. This air resistance explains why you have to keep pedaling to maintain your constant speed. If someone were to examine the air that you have left behind you after you have passed through it, they would find that the air's velocity is
A) zero everywhere.
B) straight northward everywhere.
C) zero on average but that it is swirling rapidly in all directions.
D) straight southward everywhere.

Question

Quizplus · Accepted Answer

The air left behind a moving object like a bicycle is not stationary or moving uniformly in one direction. Instead, it tends to swirl or create vortices due to the object displacing it as it moves through. This swirling motion is a result of the complex interactions between the air molecules and the object, leading to a mix of speeds and directions in the air's movement, hence "zero on average but that it is swirling rapidly in all directions."

You Are Out for a Bicycle Ride on a Calm