When are force and acceleration at their minimum in simple harmonic motion?

Since F = M a    force and acceleration both have maximum and minimum values at the same point in their motion.

Also, F = - k x    where x is the extension of the displacement that creates the acceleration.

Since, there is no force acting on the object at the midpoint of the motion, then F = - k x = 0 and there is no acceleration.

Likewise, at maximum extension F = - k x is a maximum and both the force and acceleration have their maximum values at maximum extension.

They coasters are in tear-drop form because of physics. if the ride was in a complete circle, how would the coaster get into the loop, let alone get out of the loop? also, the reason why most coasters are in tear-drop form is because of acceleration. the steeper the turn, the faster the ride.