Quirks are pretty consistent if you figure out the set of internal rules that each one works on. Like well, if we're going to really, really nerd out, the rules of Ochako's quirk are:
0. an object is "something you'd call an object in normal life". I shouldn't need to define this out but people go "what if she removed the gravity of the earth" so might as well get it out of the way
1. Ochako's quirk activates when she touches the pads on five fingers to an object
2. it makes her motion sick, creating a weight limit, but that weight limit can be trained away
3. anything under the effects of zero gravity stops falling towards the ground
4. anything under the effects of zero gravity can be picked up, thrown, or moved effortlessly
5. but they still affect other objects as if they have weight, especially in collisions
If you tried to work this out in terms of inertia and mass, it's gonna be an elaborate mess. But you don't need to. They're consistent, and if there's a weird situation (what happens in space?), you can bend the rules or make new ones to fill it out. Quirk users don't automatically know what their full power is, and since Ochako's never been to space, she wouldn't either.