In a linear model, mass can be seen as a resistance to a force.

F = ma or acceleration = Force / mass

But physics tends to ignore the other motions. Ignore the non-euclidan geometry. And in some of those, Newton doesn't hold up.

An example is that E-M drive that guy thought up. A microwave horn into a specifically designed cone, and it makes a force where there is no equal and opposite force.

All my stuff is in storage :-( But, the secret space program has flying saucers that work off similar mechanics.