1. Normal and Frictional Forces
Physics 20
Normal and Frictional Forces

2. Normal Force -Fn
The supporting force exerted by a lower surface on an upper surface.
Basically – the force acting against the force of gravity to balance it.
Drawing page 179 – SNAP book
The normal force always acts perpendicular to the surface of the object it is acting on.
The normal force acts against the force of gravity to balance it out so Fn = Fg = mg

3. Frictional Forces Act in the opposite direction of motion Depend on
The normal force
The nature of the two surfaces (μ)
Coefficient of friction
μs = coefficeint of static friction
μk = coefficient of kinetic friction
Basically, it takes more force to get an object moving than to keeping it in motion once it has started moving. That is the difference between the coefficients

4. Force of Friction Ff = μFn Ff = Force of friction Fn = Normal force
μ = coefficient of friction
Example: A 7.6 kg object is pulled along a horizontal surface. If the coefficient of friction between the surfaces is 0.20, what is the force of friction?

5. Assignment Reading Questions Pearson Physics pgs 169 – 189
SNAP Pg : #’s 1-5