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Physics 151 Week 11 Day 1
Topics: Systems and Friction
What do we know about Friction Force?
Does our model of friction depend on area?
Does real-world friction depend on area?
Static & Kinetic Friction - Part II
Describe what is happening to the forces on the box and the
effect of the forces on the motion of the box from the pictures.
Slide 4-19
Static & Kinetic Friction - Part III
Below is graph of the friction force exerted by the table on
the box.
A. Label times a-f that match the free-body diagrams in the
previous problem.
B. If the mass of the box is 3.0 kg, the maximum Ffs is 10 N,
and Ffk has an average of 6.0 N, find the coefficients of
static and kinetic friction.
Slide 4-19
Haul the Crate
A 10 kg wooden crate is placed on wood slats in the back of
a pick-up truck with no tail gate.
How fast can the truck accelerate before the crate falls off?
Assume the coefficient for static friction for the crate on the
wood slats is 0.40 and the coefficient for kinetic friction is
0.20.
Parking on a Hill
A. If you park on a hill with a 10 degree slope with the car
held by the parking brake, what is the magnitude of the
frictional force that holds your car in place?
B. The coefficient of static friction between your car's
wheels and the road when wet is 0.30. What is the
largest angle slope on which you can park your car in the
rain so that it will not slide down the hill?
C. The coefficient of kinetic friction between your wheels
and the wet road surface is 0.25. If someone gave your
your car a push on the wet hill and it started sliding
down, what would its acceleration be?
Slide 4-19
Penguin in a box
A loaded penguin in a box, together weighing 60 N, rests on a plane
inclined at 20° to the horizontal. Between the box and the plane, the
coefficient of static friction is 0.26 and the coefficient of kinetic friction
is 0.15.
1. What is the minimum magnitude of the applied force F,
parallel to the plane, that will prevent the sled from
slipping down the plane?
2.
2.
Circular Motion terminology
Radial Direction
Tangential direction
Frequency
Period
Radial acceleration
Tangential Velocity
Uniform Circular Motion
Slide 6-13
Forces in Circular Motion
v = wr
v2
A = — = w2 r
r
Fnet = ma =
{
mv2
—, toward center of circle
r
}
Slide 6-21