Section 3.2
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 What
causes motion?
 What
causes motion to stop?
 What
is friction?
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 Suppose
two students are arm wrestling,
and neither can bring the other arm
down.
 What can you infer about the forces
being exerted?
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 Newton
is recognized as the first person
to state the relationship between motion
and forces.
 He observed that and object at rest stays
at rest until an outside forces causes it to
move.
 He also observed the opposite.
 An object at rest will remain at rest and
an object in motion will remain in motion
unless acted upon by an outside force.
 When
you sit in a chair many forces act
on you.
• Atmosphere
• Chair
• Gravity
 All
of the forces are balanced therefore,
you sit comfortably and you don’t move.
 Your body is resisting change or
experiencing inertia.
 To come out of inertia a force must be
applied.
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 What
happens when you ride a bike?
 How does the bike start to move?
 Does it stay in motion even when you’re
not doing anything?
 Forces can change the speed, direction,
and overall movement of bike.
 What forces are acting on the bicyclist in
Figure 3.7?
 What would happen to the bicyclist when
the bike stopped?
 If
everything stayed in motion until a
collision caused it to stop or change
direction, what would the world be like?
 Friction acts in the opposite direction of
motion.
 Friction is an outside force that resists
motion when two surfaces come in
contact.
 Without
friction, we couldn’t walk without
slipping.
 Friction plays an important role in all
aspects of life.
 There are three main types of friction:
• Sliding Friction
• Fluid Friction
• Rolling Friction
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 This
occurs when two solid surfaces slide
over each other.
 The friction is determined by the weight
of the object and the type of surface it
moves over.
• Heavier objects exert more pressure on the
surface therefore the sliding friction will be
greater.
 Which
type of surface would cause less
sliding friction?
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 Air, water, and
oil are all fluid.
 Fluid friction occurs in type of fluid.
 It is very present when an object falls
through the air.
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 Rolling
friction- friction produced when
an object rolls over a surface.
 Force needed to overcome rolling friction
is less than the force needed to overcome
sliding friction.
 Tread on tires can affect rolling friction.
Looking at the tires on page 62, which tire
do you think will create more rolling
friction?
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 Many
machines use techniques to reduce
friction to help save the parts.
• Ball bearings
• Fluids (air, gas, liquid film)
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1.
2.
3.
4.
What is Newton’s first law of motion?
Explain how a dog overcomes inertia
when it gets up after napping on the
floor.
Explain how friction works to keep
bicycle tires from sliding on the road.
Identify two examples each of an object
at rest and of an object in motion. Use
examples of things in your school.
Explain how Newton’s first law applies
to each example.
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