So In my last Physics Exam I had one of these question which annoyed me a lot,
"Is Motion is zero but acceleration is not zero ? If no , Why not ?
I answered that it is impossible with some line of reasoning . They gave me zero marks . They gave me a example .
"Imagine there is a ball lying on the ground on earth.The ball is standing still with no motion.But ther is still an acceleration vector pointing downwards from the ball with a magnitude of $9.8$ ms$-2$.So there is acceleration without motion."
I can just put this on my test next time and get full marks , but I still have many doughts about this reasoning.
For example , If the ball has zero motion , the ball is not moving . And we know acceleration is defined by velocity and velocity is defined by motion.So,If there is zero motion ,there is zero velocity , If there is zero velocity ,then there is zero acceleration.My reasoning is that , there is indeed a force on it acting on the ball by the earth , but because the ball is on the ground ,there is a normal opposite force action on the ball ,canceling the original force.So the net force is zero .We know that $a$ = $F$ / $m$ .So If there is no force ,then there should be no acceleration.
Is there a flaw in my reasoning?