Download Unit IV Friction student copy

Friction
I. Friction
A. Background
1. A force that acts _________ the direction
of movement
2. Friction _____________________ and
causes heat
3. The normal force is the force between 2
objects in _______________ with each other
4. On a horizontal surface, the normal force
acts ______________________to the force
Fg
of gravity (weight, Fg)
Fn
B. Coefficient of Friction
1. The force due to friction, Ff, and the
normal force, Fn, have a direct
relationship
2. Coefficient of friction, ______________,
has no units
3. Formula: ______________
C. Static and Kinetic Friction
1. Static friction  Force that opposes the
_______________________
2. Kinetic Friction  The friction between
objects in contact when they are
___________
3. Kinetic friction decreases as motion
begins
4. Coefficient of friction is greater for static
friction than kinetic friction
Examples
Wood
10kg
What is the
force of friction
needed to make
the object move
from rest?
Wood
What is the force of
friction needed to
keep the object
moving?
 4. A sled sits on packed snow. The coefficient of kinetic
friction is 0.12. If a person and the sled together weigh 650N,
what force is needed to pull the sled across the snow at
constant speed?
 5. A 1.4kg block slides across a rough surface such that is
slows down with an acceleration of 1.25m/s2. What is the
coefficient of kinetic friction between the block and the
surface?
 The diagram shows a 4kg object accelerating at 10 meters
per second squared on a rough horizontal surface. What is
the frictional force acting on the object?
a = 10 m/s2
Frictional Force, Ff
M = 4kg
Applied force, 50N
D. Friction on an Incline
1. On an incline, weight still acts straight
downward, towards the surface of the
earth.
 8. Stacie, who has a mass of 45kg, starts down a slide that has
an angle of 45º with the horizontal. If the coefficient of
kinetic friction between Stacie’s shorts and the slide is 0.25,
what is her acceleration?