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Targets
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define what causes friction
Do Now
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calculate the different states of friction
put solutions to homework on board
Homework
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p. 141; Practice E; 1-4
Experiment 4.3 informal report
Static Friction
• the force that resists the initiation of
sliding motion between two surfaces
that are in contact and at rest
Kinetic Friction
• the force that opposes the movement of
two surfaces that are in contact and are
sliding over each other
Frictional Forces
• oppose the direction of motion (kinetic)
• provide equilibrium (static)
• parallel to the surface
• proportional to the normal force
• due to electrostatic forces between
atoms
Coefficient of Friction
• the ratio of the magnitude of the force of
friction between two objects in contact
to the magnitude of the normal force
with which the objects press against
each other
•μ
•μ
k
= Fk / Fn
s
= Fs,max / Fn
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Pyro’s blast knocks Iceman, whose mass is
90 kg, down and he slides backwards
across the frozen lake with an initial velocity
of 11 m/s. Assume Iceman is made of ice
(μk for ice on ice is 0.03). How long does it
take Iceman to stop sliding backwards if the
only force acting upon him is friction?
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