Aim: How does friction affect an objects motion? Do Now: Quiz HW: Problem set

How are all 3 related? mg FG W ALL 3 ARE THE SAME!!!! They are ALL Force due to gravity!

DEMO: Textbooks

Friction Demo Friction is a force that opposes motion. Two kinds of friction: Static and kinetic Ff = μFn FP If we add mass, will μ increase, decrease or stay the same? Pull an actual block with some mass. Draw FB diagram and solve for Ff. If pulled at constant speed, is it in equilibrium? YES!

FACTS of Friction Represented by the Greek letter: µ (mu) Coefficient of Friction (µ ): How much materials STICK TOGETHER Has NO Units What if I make it larger? The HIGHER the coefficient, the MORE two surfaces STICK TOGETHER Tell class they are going to prove this is true for next Lab.

Example A 65 kg skier is sliding along a horizontal patch of snow with a coefficient of friction of 0.05 at a constant speed. Draw a FBD! How much force must be applied to keep the skier moving with this constant velocity? When the ski finally stops, describe the force needed to make it move again.

Down the Slope Inclined Planes What is an inclined plane? A tool used to move objects from one height to another. Allows for the movement of an object without lifting it directly against gravity.

How do we draw a Free Body Diagram? Hint: The block is in equilibrium! See demo of block on ramp in class…

Friction Demo We know μ and that W = 2N, so lets calculate the Ff. FGx = .28N, Fgy = 1.98N We calculate Ff = μFn. Using Fgy = Fn and μ we calculate it. Then measure Force to pull up ramp. Fp + Ff + FGx = 0 at constant speed. Ff = μFn

Inclined Plane Facts The components for the Gravitational Force are SWITCHED!!! PARALLEL to the ramp is Fg sin θ PERPENDICULAR to the ramp is Fg cos θ FN Fg cos θ Fg sin θ Fg Ff

Fg on Inclined Plane

Exit Card 1. If the block on the ramp was moving at a constant velocity, what would be the sum of its forces in both the x and y direction? 2. Does surface area affect friction? Explain.