String Theory: A Matter of Mass

When you read that the force between objects is proportional to the mass of the two objects, you might think that this means that heavy objects fall faster than lighter objects. For example, doesn’t a bowling ball fall faster than a soccer ball?
In fact, as Galileo demonstrated (albeit not with modern bowling balls and soccer) years before Newton was born, this is not the case. For centuries, most people assumed that heavy objects fall faster than light ones. Newton was familiar with Galileo’s results, which is why he was able to figure out how to determine force the way he did.
According to Newton’s interpretation, it takes more force to move a heavier object. If you drop a bowling ball and a soccer ball from a building (which is not recommended), they will accelerate at exactly the same rate (ignoring air resistance) – about 9.8 meters per second.
The force acting between the bowling ball and the ground will be higher than the force acting on the soccer ball, but because it takes more force to move the bowling ball, the actual rate of acceleration between the two is identical.
Realistically, if you did the experiment, there would be little difference. Because of the air resistance, a lighter soccer ball will likely slow down if dropped from a high enough point, while a bowling ball will not. But a properly constructed experiment, in which air resistance is completely neutralized (as in a vacuum), shows that objects fall at the same rate, regardless of mass.