Transcript Friction Quiz  Laws of Dry Friction  Coefficients of Static vs.

Friction Quiz
 Laws of Dry Friction
 Coefficients of Static vs. Kinetic
Friction
 Impending Motion, Angle of Friction
1. Which statement best defines
dry friction?
a) The force parallel to the surface of two
objects in contact with each other.
b) The normal force of two objects in
contact with each other.
c) The perpendicular force of two objects
in contact with each other.
d) The force that resists an object rolling
across a surface.
2. What horizontal force starts
the object moving, if it weighs
50.0 kg and mstatic=0.60?
a) 50.0 N
b) 83.3 N
c) 294 N
d) 491 N
F a p p lied
W = w e igh t
F fr ic tio n
F n o rm a l
3. What is the normal force in the
following figure if W=200 N and
Fapplied=100 N?
a) 100.0 N
b) 106.0 N
c) 165.8 N
d) 200 N
F applie d
   
W
F fric tio n
n
F n orm al
+
t
4. What is the maximum
frictional force in the figure below if
W=200 N, Fapplied=100 N and
mstatic=0.60?
a) 99.5 N
b) 106.8 N
c) 165.8 N
d) 200 N
F applie d
   
W
F fric tio n
n
F n orm al
+
t
5. What is coefficient of kinetic
friction in the figure below if
Fhorizontal=200 N, Fvertical=650 N,
W=800 N and the object is moving?
a) 0.200
b) 0.308
c) 0.600
d) 0.250
F a p p lied
W = w e igh t
F h o rizo n ta l
F v e rtic a l
6. Compute the coefficient of
static friction from the following
figure assuming slippage is about to
occur.
a) 0.902
b) 0.477
c) 0.445
d) 0.431
W = 50 .0 N
25 .5 d e g
Correct answers
1)
2)
3)
4)
5)
6)
a
c
c
a
b
b
(tangential or parallel force)
(=50.0 x 9.81 x 0.60)
(=200 – 100 sin20°)
(=165.8 x 0.60)
(=Fh/Fv = 200/650)
(=tan 25.5°)
Rank yourself
 5-6: Consider tribology (friction
science) as a career.
 3-4: Check that your calculator is
using the metric system.
 0-2: You are on a slippery slope,
increase your normal forces and
study habits.