Friction

What is friction?

Answer Me!!!

Think of two factors that affect friction.

Friction

Friction is the force that opposes relative motion of two objects in contact.

Block

Surface

Block

Surface

Coefficient of Friction

The frictional interaction between two surfaces is measured with the coefficient of friction.

The bigger the coefficient of friction, the “stickier” the two surfaces will be together.

Types of Friction

Static Friction is the force that opposes the start of motion.

Kinetic Friction is the force that opposes two that are in motion.

kinetic friction < static friction

Normal Force

The Normal Force (FN) is the force pressing two objects together.

On a horizontal surface, FN = -FG

FG = mg

FN = -mg

Force of Friction

Where Ff is the Force of Friction

FN is the Normal Force And is the coefficient of friction

Nf FF

Final Thought…

A 2kg rubber block is being dragged across a horizontal ice rink at a constant velocity. Calculate the force of friction acting on the block.

Answer Me!!!

How will the weight of a crate affect the frictional force acting on that crate?

Answer Me!!!

A 10 N wooden crate is being dragged across a horizontal wooden surface at a constant speed of 4 m/s. How much force is being used to pull the box?

Friction on an Incline

If an object is on an inclined surface, the normal force (FN) is equal to the component of FG that is perpendicular to the surface.

cosGN

GN

FF

FF

FN

FG

FG_|_

Constant Velocity

When an object moves at a constant velocity:Acceleration = 0 m/s2

Net Force = 0 NForce Pulling = Force Resisting

Answer Me!!!

A 12 N block slides down a 20o incline at a constant speed. What is the coefficient of friction between the block and the incline?