Complex sentence: A heavier disc will have less air resistance than a lighter disc however due to the force required to accelerate the disc being directly proportional to the mass of the disc this will decrease the acceleration of the disc, assuming that the force of projection is constant.
Split into simpler sentences: A heavier disc has less air resistance than a lighter disc, because the force required to accelerate the disc is directly proportional to the mass of the disc. This decreases the acceleration of the disc, assuming that the force of projection is constant.