september 25, 2009 bellringer would it be better if the floor at the skating rink had carpet on it?...
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September 25, 2009
Bellringer
Would it be better if the floor at the skating rink had carpet on it? Explain.
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http://www.youtube.com/watch?v=R7JMBqgl0Hc
http://www.youtube.com/watch?v=AX_lCOjLCTo
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4.2 Friction
• Friction is a force that resists the motion of objects or surfaces.
• Many kinds of friction exist.
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4.2 Four Types of Friction2 Forms of Fluid Friction
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Vocabulary
Friction: A force that resists motion.
Sliding Friction: The friction force that
resists an object moving
across a dry surface.
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VocabularyStatic Friction: The friction force that resists
the motion between two
surfaces that are not moving.
Rolling Friction: The friction force that
opposes the motion of any
body rolling over the surface
of another.
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Vocabulary
Fluid Friction: The friction force in which at least one of the objects is a fluid. (either gas or liquid)
Air Friction: The resistance of motion through air.
Liquid Friction: The resistance of motion through
a liquid.
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4.2 Friction• Friction depends on both of the surfaces in
contact.• When the hockey puck slides on ice, a thin
layer of water between the rubber and the ice allows the puck to slide easily.
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4.2 Identifying friction forces
• Friction is a force, measured in newtons just like any other force.
• Static friction keeps an object at rest from moving.
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• Sliding friction is a force that resists the motion of an object moving across a surface.
4.2 Identifying friction forces
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4.2 Reducing the force of friction
• Unless a force is constantly applied, friction will slow all motion to a stop eventually.
• It is impossible to completely get rid of friction, but it can be reduced.
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4.2 Reducing the force of friction
• The friction between a shaft (the long pole in the picture) and an outer part of a machine produces a lot of heat.
• Friction can be reduced by placing ball bearings between the shaft and the outer part.
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4.2 Useful friction
• Friction is also important to anyone driving a car.
• Grooved tire treads allow space for water to be channeled away from the road-tire contac point, allowing for more friction in wet conditions.
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4.2 Useful friction
• Shoes are designed to increase the friction between their soles and the ground.
• Players wearing cleats can apply much greater forces against the ground to help them move and to keep from slipping.
Why do you think these shoes increase friction?
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4.2 Friction and energy
• Friction changes energy of motion into heat energy.
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4.2 Friction and energy• Friction is always
present in any machine with moving parts.
• If the machine is small, or the forces are low, the amount of heat produced by friction may also be small.
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Identify the types of friction
1. Static Friction _____2. Fluid Friction (gas) _____3. Rolling Friction _____4. Sliding Friction _____5. Fluid Friction (liquid) _____
D
B
E
A
C