The Concept of Relative Motion
In classical physics, the terms 'rest' and 'motion' are not absolute properties of an object. Instead, they are relative to a chosen frame of reference (or observer).
The Answer
Yes, an object can be said to be at rest and in motion at the same time, provided it is being observed from different frames of reference.
Intuition and Example
Imagine you are sitting on a train traveling at a constant velocity along a straight track.
- Perspective 1 (Inside the train): If you look at a book placed on the seat in front of you, the book is at rest relative to you because your distance from the book is not changing over time.
- Perspective 2 (Outside the train): If a person is standing by the side of the tracks, they see both you and the book moving past them at the speed of the train. To this observer, the book is in motion.
Why This Happens
Motion is defined as the change in position of an object with respect to time and a reference point. If the coordinate system chosen to define 'position' shifts, the description of motion must also change. Because we can choose any object as a reference point, the same physical event can yield different descriptions of state (rest or motion) simultaneously.
Conclusion
There is no 'absolute rest' in the universe. Everything is moving relative to something else. Therefore, rest and motion are always relative states.