Can you explain once again how the bowling ball and the tennis ball drop at the same time. Are weight and mass proportional? If mass is the resistance to acceleration and weight is a gravitational force pulling down on the ball, doesn't the weight of the bowling ball make it fall faster? Or does the bowling ball's increased mass in a way cancel out the bowling ball's increased weight?  HC 

Weight and mass are proportional to one another and the bowling ball's increased mass does effectively cancel out its increased weight. Let's suppose that the bowling ball is 100 times as massive as the tennis ball—meaning that it takes 100 times as much force to make the bowling ball accelerate at a certain rate as it does to make the tennis ball accelerate at that same rate. Because weight is proportional to mass, the bowling ball also weighs 100 times as much as the tennis ball. So if the only force on each ball is its weight, each ball will accelerate at the same rate. The bowling ball will experience 100 times the force but it will be 100 times as hard to accelerate. The two factors of 100 will cancel and it will accelerate together with the tennis ball.