It was Isaac newton who discovered that all falling bodies accelerate at the same rate. His second law of motion states that the greater an object’s mass, the greater the force required accelerating it. A bowling ball weighing 7kg is pulled to Earth by a gravitational force 100 times as strong as a 70g tennis ball. However, because the bowling ball’s mass is 100 times greater to start with, the acceleration of the two balls will be exactly the same.
Most of the time, people ask this question with the idea of a Newtonian “feather vs. bowling ball” concept in mind. Based on those terms, the typical answer is correct: two objects will fall at the same speed in a vacuum, and air resistance can appear to make an object fall slower. However, there is a surprising, but more complicated nuance to this problem.
Every action has an equal and opposite reaction. This means that, just as the Earth is exerting a gravitational force on the objects, the objects are exerting a gravitational force on the Earth. Just as much as the objects fall onto the Earth, the Earth falls onto the objects as well. It’s just the fact that the Earth is so much larger and more massive that we default to viewing things from the first perspective and not the latter. Nevertheless, the gravitational force exerted on the Earth by the objects cannot be ignored. Gravitational force is determined by the Universal Gravitation law:
Where m and M are the two masses involved in the interaction. If we do two separate calculations, one for the mass of the lesser object, and one for the mass of the greater object, we can see that there will actually be a larger gravitational force involved with the more massive object.
This is where most people would interject that, well, yes, the larger mass needs a larger force in order to achieve the same acceleration. But reverse the frame of reference; now let’s consider this from the point of view of the objects doing the pulling, instead of the Earth. Now we can see that the force exerted by the larger mass is doing more.