Is it possible to turn off the friction or gravity on a object so it would move forever yet still have physics interactions with other objects?

Context please.

But, in any case, what I'm learning in physics is that an object's acceleration is controlled by the SUM of forces acting on it. So, the sum of forces would be everything except friction and gravity.

So, I'm basically just saying yes. But it seems like there's something you're not mentioning.

EDIT:
PhysX is an engine, right? Forgot. If you meant the engine, disregard what I said. I know NOTHING about it, and momentarily thought you were using shorthand.

Friction is a per-material property in PhysX, you can turn it off for an actor by assigning it a material with no friction. If you want an object to move forever, you also need to set linear damping to zero for that actor. Setting angular damping to zero will also allow it to rotate forever.