If an observer was trapped in a closed box with no way to interact with the external surroundings how will he know if he is moving or at rest

Question

I am a high-school student. Recently we learned the concepts of relative motion and velocity. The idea that anything in motion can subsequently be at rest depending on the frame of reference fascinates me. I am however unsure about a thought experiment I conceived . If an observer was trapped in a closed box with no way to interact with the external surroundings how will he know if he is moving or at rest ( by moving i mean with a constant velocity )? Is there any way to know as motion is relative? What noticeable (noticed by the observer) effect will a force applied on the box have on the observer?

Answer 1

how will he know if he is moving or at rest

He can't. The two situations are indistinguishable.

If the box is in uniform (constant velocity) motion, there is no way the person inside can sense how fast he is going, or if he is at all.

The human body can only sense accelerations.

Is there any way to know as motion is relative?

If, as your question states, the person in the box has no way to communicate with the outside of the box, then no. The fact that motion is relative is not really the point here. The point is that provided no (net) forces operate the box, there is no way to tell.

What noticeable (noticed by the observer) effect will a force applied on the box have on the observer?

Because of inertia, any force will cause a feeling of "motion" that is usually in the opposite direction of the applied force. For example, if a force is applied accelerating him forward, he will feel a backward jerk. If the force is applied in the opposite direction, he will feel a forward push.

Answer 2

This is the essence of Einstein's conception of special relativity: the laws of physics do not make any distinction between being at rest (relative to what?) and moving at constant velocity (again, relative to what?). This means there is no physics experiment you could perform from inside that box that could possibly tell you if you were sitting still or moving at constant velocity.

Answer 3

Your inner ear will tell you, it will pick up the motion, be it ever so slight, but one symptom that you may feel is nausea or get a sore head. I get a form of morning sickness from a genetic condition I have and if I cannot see where I am going, or I am pointing in another direction from the way I am moving I feel nauseous.