Show Me The Physics Website - Intro to Friction Notes

Left or right. Which experiences the most friction? Why?

Friction

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D) Friction - force between 2 surfaces that opposes motion

Depends only on:

1) texture of each surface

What do plows have on their wheels to increase friction?

Chains

2) force holding objects together

What do race cars have mounted on their rear hood to increase their friction?

Spoilers increase the force between tire and road

Why do some people
put barbells in their
car trunk on a snowy
day?

Weights in a car truck
increase the tires force on the road

Two Kinds of Friction

(f_s) 1) Static Friction - force of friction that must be overcome to move an object at rest.

(f_k) 2) Kinetic Friction - force of friction that opposes a moving object.

Kinetic friction is weaker than static friction

f_k< f_s

Friction Equations

Static friction: f_s = u_sF_n

Kinetic friction: f_k = u_kF_n

f_s = force of static friction

f_k = force of kinetic friction

F_n = normal force (supporting force)

u_s = coefficient of static friction - "the roughness number"

u_k = coefficient of kinetic friction - "the roughness number"

1. Relates to texture of surfaces in contact

2. Calculated in lab

ice and skate - low uk

What do skiers do to
their skis to lower the coefficient of friction between their skis and
the snow?

Skiers put wax on the bottom
of their skis to lower the coefficient of friction

What is the direction of the friction at P?