My teacher explained to my class that Normal force equals Force of Gravity. Given a free body diagram on a flat surface, Normal force is directed up, and Force of Gravity is directed down.
So my teacher did the following:
Fg = Force of gravity
Ff = force of friction
Fn = normal force
u = co-efficient of friction
Ff = uFn
Ff = uFg
Ff = u*m*g (mass times gravity)
How is this possible? normal force is equal to the force of gravity? but they oppose each other, don't they?
Thank you so much for any help at all.