# Why does mass cause resistance to acceleration?

If I were in a vacuum with no gravity or friction, why would it be harder to push a floating bowling ball than a marble? Is there anything happening on an subatomic level that makes matter act differently when it's pushed together? How would matter know to act different unless it somehow interacted with it's environment?

• If there was no resistance against acceleration, then everything would be moving infinitely fast. That would be a completely different World, if any. – Steeven Mar 19 at 12:04
• @Steeven Thank you for your answer and I feel like it is an adequate explanation of the consequences if there were no resistance to acceleration. Do you know if science has provided an explanation as to why more massive objects are harder to accelerate. I understand that that's just the way it is, but it's difficult to feel satisfied with that answer. It seems odd that you start to pack these atoms together and they begin to resist acceleration intrinsically. Wouldn't the atoms need to be interacting with the environment in some way to become different from a non-packed set of atoms? – Matthew Cochran Mar 19 at 13:02
• Atoms don't begin to "resist acceleration" when you "pack them together." Each individual atom has mass. Each individual atom has inertia (i.e., resists acceleration). The only reason why a bowling ball has more inertia than a marble is that the bowling ball contains more atoms. Their inertias add up. – Solomon Slow Mar 19 at 13:05
• @SolomonSlow Wow, thank you. That was simple. So, I guess the same would apply to atoms. The reason a hydrogen atom is easier to push than a lead atom would be because you're stacking protons and neutron with additive inertia? Thanks for your time. – Matthew Cochran Mar 19 at 13:14
• We don't know why, we just know from observation that it is the case. Someone once saw that "resistance against acceleration" is a thing of this World - and named it Newton's 2nd law. It turned out that the "more" there is of something, the tougher it is to accelerate. This "more" was then named (inertial) mass. As always, all of physics starts from a set of initial, empirical observations. Such observations may explain everything else - but there is nothing more fundamental to explain them. If there was, then how would you explain that? There will always be an unexplained why. – Steeven Mar 19 at 14:50