Question

An observer sees an airplane flying at a fast, constant speed along a straight path. However, a passenger inside the airplane feels that they are not moving at all.

What explains the difference between what the observer is seeing and what the passenger is feeling?

A.
The acceleration of the observer is in the opposite direction of the motion of the airplane, so the net force on the observer is decreasing.
B.
The observer is moving at the same velocity as the plane, so the net force on the observer is zero.
C.
The acceleration of the passenger is in the same direction as the motion of the airplane, so the net force on the passenger is increasing.
D.
The passenger is moving at the same speed as the plane, so the net force on the passenger is zero.

Answer 1

D.

The passenger and the airplane share the same velocity, so there is no acceleration (no net force) on the passenger. Sensation of motion comes from acceleration (forces acting on your body), not from constant velocity. The outside observer sees relative motion, but because the passenger is moving with the plane at constant speed in a straight line, they feel at rest inside it.