In a vacuum, gravity acts on different mass exactly the same. However, what about on earth.....what is the relationship between two identical sized objects, in the exact same atmosphere.....but of different mass? For example, dropping two identical sized bowling balls from height of 10 meters, one ball is 10kg, the other is 20 kg. Is there a formula for speed or acceleration? Or, would the formula be impossibly complex because it is different for every set of object, due to differing coefficients of drag? Real World example- I'm about 245 pounds. My friend is about 175 pounds. When we go mountain biking, on the downhill sections....we both coast. Well, I've noticed that I end up passing him very quickly, or must stay on my brakes if I wish to stay behind him. Clearly, assuming everything other than our mass is the same (my drag should actually be slightly more than his, just due to my size..but let's pretend it's not), yet I'm accelerating faster than he is. Or.....maybe something else is at work?