Friction
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Understanding Friction: Static and Kinetic, Coefficients, and Applications, Slides of Physics
An in-depth exploration of friction, including its types (static and kinetic), formulas, coefficients, and practical applications. Learn about the role of normal force, the difference between static and kinetic friction, and how to measure coefficients using real-world examples.
Typology: Slides
2012/2013
1 / 11
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Friction
Holding in Place
Objects on an incline will often stay put.
There must be a force that holds the object in place.
Static friction
is from the contact of resting objects.
•^
Force holds up to a certain point
-^
Force is based on the type of contact (rough, smooth)
-^
Maximum force is proportional to the pressing force of theobject (normal force)
Coefficient of Friction
m
F 1 T
mg
F^
s
fr
(max)
Use rope and measure theforce when movementbegins.•
Measure weight
-^
Measure force at slippingpoint.
W
F
mg
F
F
mg
T
T
s
T
s
/^
Slippery Slope
If^
F
fr^
Fs
N^
mg s
cos
then the block will hold.
At equality the block justbegins to move.
F^ N
^ mg Fg
cos mg
sin mg
sin
(max)
mg
F
fr^
tan
cos
sin
s
s N s
fr
mg
mg
F
F
Static vs. Kinetic
Static and kinetic friction aresimilar.•
Force in opposite directionto motion
-^
Proportional to normal force
-^
Coefficient of frictiondepends on materials
Static and kinetic friction aredifferent.•
Static friction is an inequalityup to a maximum
-^
Coefficient of friction istypically greater for staticfriction at the same surface
-^
Wood on wood (0.4 vs. 0.2)
Downhill Skiing
A TV station has invited youto be the sciencecommentator for anupcoming ski race. Youobserve that a skier needs atleast 3° of slope to moveforward at a constantvelocity.
What is the coefficient offriction on the skis?
°
Minimum Sliding
When the skier is slidingslowly we can neglect airresistance.
Kinetic friction balances thecomponent of gravity pullingforward.
°
Fgx
= mg
sin
FN
= mg
cos
Ffr
= -
k
F N
tan
cos
sin
k
k
fr
gx
mg
mg
F
F
Normal Force and Friction
Friction depends on both the normal force and on thecoefficient of friction.
To reduce friction requires reducing one of thosefactors.
•^
Reduce normal force by lightening the load
-^
Reduce normal force by adding additional upward force
-^
Add a lubricant to reduce the coefficient of friction