Warm-Up October 26, 2015 Super Sliders and other similar products claim to allow you to effortlessly...
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Transcript of Warm-Up October 26, 2015 Super Sliders and other similar products claim to allow you to effortlessly...
Warm-UpOctober 26, 2015
“Super Sliders” and other similar products claim to allow you to “effortlessly slide heavy furniture.” How do they work?
Free Body Diagram Answers
Force Situations Worksheet
FrictionSection 5.2
Two Types of FrictionKinetic Friction: When an
object is movingStatic Friction: When an object
is not moving (stationary)
(There are other types of friction that we will not discuss in this course.)
Kinetic FrictionKinetic friction is always in the
opposite direction of the object’s motion.
Depends on the Normal Force () and the types of surfaces that are sliding against each other
The Coefficient of Kinetic Friction () is a numerical property of the surfaces.
= Greek letter “mu”
Kinetic Friction Force
Nkkf FF ,
Example 1You are pushing a 20.0 kg box
horizontally at a constant speed of 2.0 m/s with . How much force do you exert on the box?
You-Try #1You are pushing a 25.0 kg box
horizontally with a force of 125 N. The coefficient of kinetic friction is 0.35.
a) What is the force of friction?b) What is the resulting
acceleration?
Warm-Up: October 27, 2015
A 30.0 kg box is being pushed at a constant speed on a horizontal surface with
Draw a free body diagramCalculate the force of
gravityCalculate the normal forceCalculate the force of
frictionCalculate the push force
Static FrictionStatic friction is always in the
direction that makes .Depends on the Normal Force (),
the types of surfaces that are in contact, and the magnitude of the applied force(s).
The Coefficient of Static Friction () is a numerical property of the surfaces.
= Greek letter “mu”
Static Friction Force
NSsf FF ,If there is a force trying to cause
motion, the static friction force will increase up to a maximum value before it is overcome and motion starts.
Example 2A 30.0 kg box is at rest on the
floor. If the coefficient of static friction is 0.55, what is the maximum push force you could apply to the box before it starts moving?
You-Try #2A 15.0 kg box is at rest on
the floor. If you have to push with a force of 95 N before the box starts to move, what is the coefficient of static friction?
Friction CoefficientsFor a given surface combination,
the coefficient of static friction will always be larger than the coefficient of kinetic friction.
It’s harder to get something to start moving than to keep it moving.
kS
Assignments:Read Section 5.2 of your
textbook (pages 126-130)Page 128 #17-20Page 130 #27, 28, 30Braddock House Clean-Up
Worksheet◦On website
Worksheet“Braddock House Clean-Up”
Warm-Up: October 28, 2015
A box is pushed along a horizontal floor giving the box a speed of 3.2 m/s. 1.7 seconds after the end of the push, the box stops. What is the coefficient of kinetic friction between the box and the floor?
Force Situations
October 28, 2015Read Section 5.2 of your
textbook (pages 126-130)Page 128 #17-20Page 130 #27, 28, 30Braddock House Clean-Up
Worksheet◦On website
Read Section 5.3 of your textbook