A brick and a feather fall to the Earth at their respective terminal velocities. Which object experiences a greater force of air friction?

Question

A brick and a feather fall to the Earth at their respective terminal velocities. Which object experiences a greater force of air friction?

1. The feather
2. The brick
3. Neither, both experience the same amount
4. Not enough information to determine

Make a statement to support your answer.

I don't understand why the brick is the correct answer.

Answer 1

Hi Alizee B.,

Think of it as a problem in calculation. Force (air resistance) ~= Area(effective) * v^2, I think it is. The brick has both the greater effective area (the crosssection of the brick in a plane perpendicular to the direction of falling travel) AND the greater velocity with respect to the air. Therefore, you may immediately conclude that it experiences the greater air resistance (a force).

Now, take a moment to reconcile this with your (correct) hunch that the brick falls faster, and the feather slower. It's not the air resistance alone that's responsible for the ordering of the respective terminal velocities, but rather the difference (mathematical operation) of the force of gravity on each object minus its force of air resistance. The brick has such a massive, compact profile that the relative contribution of the air resistance to the total force is minor, whereas the relative resistance for the feather is a major contribution to the total force.

-- Cheers, -- Mr. d.