inaya medical college (imc) · 2015. 4. 8. · dr. mohammed mostafa emam inaya medical college...
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DR. MOHAMMED MOSTAFA EMAM
INAYA MEDICAL COLLEGE
(IMC)PHYS 101 - LECTURE 6
Friction Force
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Key terms
• Friction force (Ff) – a force that tends to oppose
motion
• Coefficient of friction (µ) – the ratio of the friction
force to the normal force
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Force of Friction = μ · Normal Force
Ff = μ · FN
FRICTION
Weight
μ is the coefficient of friction!
Normal Force
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Key terms
• Normal force (Fn) – the force pressing two contact
surfaces together
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• Friction is a force between two surfaces that are sliding and they must in contact with each other.
• Examples: • The tyre of the lorry
is in contact with the
road.
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• Friction always works in the opposite direction from the direction of the moving object.
• Can slows a moving
object downMoving
Friction
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FORCE
• Friction Force:
Friction force results from the interactions of surfaces.
Irregularities in the structure of the matters causes friction
force.
These irregularities can be detected in micro dimensions.
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FORCE
• Friction force is always opposite to the direction of motion
and tends to decrease net force.
• All materials have their own friction constant in other words
friction force depends on the type of materials.
• Another factor affecting friction force is the normal force
(force is the reaction to the perpendicular force exerting
on it).
• When you apply a force to an object, then friction force
becomes active and resists with the force of having opposite
direction to your net force. 8
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Friction depends on…
Roughness of the surfaces.
Force that objects are beingpressed one against the other.
Weights of the objects.
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Friction produces heat.
Friction wears out the rubbing surfaces.
Friction produces noise.
Disadvantages of friction
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What is Friction?
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• Normal force equals weight on a level surface
mg
FN
Ff = mkFN = mk mg
MotionFriction
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What is the Friction Force?
• Block on an inclined plane
mg
θ
θ
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What is the Friction Force?
• Block on an inclined plane
mg
θ
θ
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How many types of Friction?
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There are four types of friction
namely:
Static friction
Sliding Kinetic friction
Rolling friction
Fluid friction
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Key terms
• Static friction – the type of friction that exists between
the contact surfaces of two bodies at rest.
• Kinetic friction – the force that opposes sliding
motion.
• Rolling friction – the force that opposes rolling motion.
• Fluid friction – the force opposes propagation of any
item in fluid.
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FORCE
•Example
50 N of force is applied to the 6 kg box. If the coefficient of friction is
0.3, find the acceleration of the box.
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- Free body diagram of the
system is given above.
- From this diagram we find the
normal force of the surface
and friction force.
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- Free body diagram of the
system is given above.
- From this diagram we find the
normal force of the surface
and friction force.
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- Free body diagram of the
system is given above.
- From this diagram we find the
normal force of the surface
and friction force.
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- Free body diagram of the
system is given above.
- From this diagram we find the
normal force of the surface
and friction force.
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