Question

Why is normal force acting down in a circular motion when the object is at top of the circle?

Answer 1

see below

Explanation:

For a roller coaster for example, there is a force between the roller coaster seat and the rider called the normal reaction force.

In terms of Newtons 3rd law = the rider exerts a force on the rollercoaster seat with an equal and opposite force to the force that the seat exerts on the rider (this is the normal force)

this force acts down because the rider is upside down. So, at the bottom of the ride the seat's normal force acts up on the person.

But because the seat is upside down at the top of the rollercoaster, the normal force acts down.

this can be applied to other situations for vertical circular motion.

I hope I didn't confuse you.