Explain why objects in free fall drop to the ground at the same speed, regardless of their mass.

An object in free fall is only subject to the gravitational force from the earth. The magnitude of this force is mg, where m is the mass of the object. Newton's second law states that the force on an object is equal to it's mass times the acceleration it experiences, F=ma. Equating the two, mg=ma, and thus a=g. The acceleration is therefore independent of mass as m does not appear in the equation of motion.