Announcements

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Announcements

• Tutorials this week
• Extra credit due date
• Pre-AP relativity discussion

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Circular motion
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Objectives

• Content
• SW understand the concept of inertia in circular
  motion.
• Language
• SW define centripetal force.
• SW Differentiate between centripetal and
  centrifugal force.

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http//www.youtube.com/watch?vhW57tLMcqt4

• Linear Speed increases when the radius or the
  rotational speed increases.

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If we swing a rock on a string over our head,
what do we have to do to keep it in motion?
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Centripetal Force

• http//www.youtube.com/watch?vqsqpuRIwxoY

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If we swing a rock on a string over our head,
what do we have to do to keep it in motion?

• Pull inward

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Centripetal Force

• A force is required to maintain circular motion
• Any force that causes an object to follow a
  circular path is called a centripetal force.
• Centripetal means center-seeking

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It isnt a new and mysterious force

• Gravitational force that holds the moon in
  orbit is a centripetal force

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It isnt a new and mysterious force

• Electrical forces holding the electrons in
  orbit around the nucleus are centripetal forces

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Motion on a flat curve

• When a car rounds a corner, the _____and _____
  provide the centripetal force

• tires
• road

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• If the tires are worn smooth, if the car is going
  very fast or the road is icy or oily, this
  friction force will not be available.
• The car will not be able to move in a circle, it
  will try to go in a straight line and possibly go
  off the road.

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Highway Curves Banked and Unbanked

• Car driving on a wall
• When a car goes around a curve, there must be a
  net force toward the center of the circle of
  which the curve is an arc. If the road is flat,
  that force is supplied by friction.

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Highway Curves Banked and Unbanked

• If the frictional force is insufficient, the car
  will tend to move more nearly in a straight line,
  as the skid marks show.

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What would happen if an object were released from
its orbit?

• Draw the direction it would travel if released at
  1 and 2

1
2
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• The object would travel tangent to the circle in
  a straight line

1
2
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Washing machines

• 1) The ___ rotates at high speed during the spin
  cycle
• 2) The tubs _______
• exert force on the clothes, but the holes
  prevent the tub exerting the same force on the
  ______.
• 3) _____ allows the water to escape in a
  straight line.

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• http//jalopnik.com/5415082/fifth-gear-brings-hot-
  wheels-to-life-sets-reallife-looptheloop-record

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Centrifugal Force

• Centrifugal force is a fictitious force - it is
  not an interaction between 2 objects, and
  therefore not a real force.
• Nothing pulls an object away from the center of
  the circle.

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Centrifugal Force

• What is erroneously attributed to centrifugal
  force is actually the action of the objects
  inertia - whatever velocity it has (speed
  direction) it wants to keep.

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What is wrong with this video?

• Video

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