What force causes a leaf to fall more slowly than a penny?

We know that air resistance (or atmospheric drag) is what causes a leaf to fall more slowly than a penny. A large leaf that weighs a much as a penny has a much greater surface area than the penny, and all this surface area means that the leaf has more drag. Though the leaf and penny will be accelerated by the same amount of force (because they have the same mass), the leaf will present all that surface area to the air, and this will set up a condition of high drag.