While gravity supposedly makes all objects accelerate at the same rate, feathers do not seem to comply. What factors affect the feather’s acceleration, besides air resistance (which should affect all objects equally)?
Actually, air resistance doesn’t affect all objects equally. The feather has so much surface area that it pushes strongly on the air through which it moves and the air pushes back. For an object with very little mass and weight, the feather experiences an enormous amount of air resistance and has great difficulty moving through the air. That’s why it falls so slowly. If you were to pack a feather into a tiny pellet, it would then fall just about as fast as other objects. Similarly, you fall much more slowly when your parachute is opened because it then interacts with the air much more effectively.