Transcript 3.3 Motion & Force - Trimble County Schools

3.3 Motion & Force
Objectives
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Explain how forces and motion are
related.
Compare and contrast static friction and
sliding friction.
Describe the effects of air resistance on
falling objects.
Force

Push or pull that one object exerts on
another
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Vector with size (strength of force) & direction
SI Units = Newtons (N)
Can cause the motion of an object to
change
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Example: hitting a tennis ball
shooting pool/billiards
Balanced Forces
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Forces equal in
size but opposite
in direction
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doesn’t change
velocity
Net Force
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When 2 or more forces act on an object at
the same time
Sum of all forces acting on an object
Unbalanced Forces
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When forces
combine to produce
a net force that is
not zero
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Forces that aren’t
equal  The object
moves
Changes the velocity
of an object
Friction
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The force between two objects, in contact,
that opposes the motion of either object
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Unbalanced force
Why does a ball stop rolling?
Why do we have to keep applying gas to the
engines in our cars to keep moving?
Better yet, why do we put oil in a car’s engine
Why do runners wear running shoes?
Why do parachutes work?
Friction
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Friction depends on the surfaces of the
objects in contact
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Smooth things tend to have less frictional force
 they are more slippery
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Ice, oil on concrete, my old shoes, my road bike
tires
Rough things tend to have more frictional force
 less slippery
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Asphalt, my new running shoes, my mountain bike
tires
Frictional Force
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Increases when the force pushing surfaces
together increases
Static Friction = frictional force that
prevents 2 surfaces from sliding past each
other
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Sliding friction = force that acts in
opposite direction to the motion of a
surface sliding past another surface
Rolling friction = similar to sliding friction
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why it is easier to move something on wheels
Friction
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Air Resistance is a form of friction
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Caused by the interaction between an object
and the air molecules it comes into contact
with
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The bigger the object the more air resistance
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The faster the object the more air resistance
Air Resistance
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Causes objects to fall at different
acceleration and speed
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Acts in opposite direction to velocity
Air resistance not mass causes objects to
fall at different rates
v
v
v
v
v
Terminal Velocity
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When an object falls with constant velocity
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Upward air resistance becomes large enough
to balance downward force of gravity
http://www.iop.org/activity/education/Teaching_Resources/Teaching%20Advanced%20Physics/Mechanics/Images%20200/img_mid_4140.gif
In-Class Assignment/Homework
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Chapter Review WKT
Can a penny kill someone? (mythbusters
episode)
Bill Nye Friction Video