Apparent motion in a convex mirror Why is it that if we look at the image of a person running with a constant velocity, in a convex mirror (for instance the rear view mirror of a car), the man's velocity  seems to be accelerated?
 A: The answer has to do with the tangential velocity with respect to the viewer.
Perhaps the simplest corollary I can offer: if you are driving down the highway, the vehicles coming the other direction at a distance do not appear to be moving quickly even though your comoving speed is 100-150mi/h, because they are moving almost directly toward you; they do not move across your field of vision very much, staying almost directly ahead. However, once they get close and pass you, they do appear to be moving quickly, because they cross a large arc of your viewing angle in a short time.
The same phenomenon happens when viewing moving objects in a convex mirror. If the runner is moving almost directly toward the mirror (coming up the sidewalk while you are parked at the curb, for example) then his image will cross only a small angle of the mirror in a long time; when he gets closer, his image begins to travel more quickly around the curve of the mirror due to its convex nature, even if he maintains the same speed. Of course, unless he runs directly into the mirror, you'll also see his image "rotate" so that you see his side rather than his front.
In both cases is the same effect - an increase in tangential velocity at a constant linear velocity. It's just more noticeable in a convex mirror because you can observe the effect without turning your head As you normally would have to.
