[Physics] If you are sitting completely still inside of a moving car are you at rest

Question

My teacher and I had an argument in class where I stated that motion is undefined without a reference point and that you could just as easily claim that the road is moving backwards at the opposite vector of the car moving forwards.

Answer 1

"At rest", when its use is attempted as an absolute term, is meaningless. The term "at rest" must always be used relative to a specific frame of reference, and different frames of reference can and will disagree as to what objects are at rest. The choice of reference frame is often implicit in the context (such as the implicit choice of a reference frame co-moving with the (local) surface of the Earth when solving everyday mechanics problems) but that choice can always be subverted by specifying a different frame as the chosen reference.

So: yes, if you're sitting completely still inside a non-accelerating car, then you can legitimately be said to be at rest in the reference frame that co-moves with the car.