Circular Motion

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Circular Motion
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Rotation and Revolution

• Rotation-Around an Internal Axis
• Earth rotates 24 hours for a complete turn
• Linear versus rotational speed
• Linear is greater on outside of disk or
  merry-go-round, more distance per rotation
• Linear is smaller in middle of disk, less
  distance per rotation.
• Rotational speed is equal for both
• Rotations per minute (RPM)
• Linear speed is proportional to both rotational
  speed and distance from the center

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Rotation and Revolution

• Revolution-Around an External Axis
• Earth revolves 365.25 days per trip around sun
• Same relationship between linear and revolutional
  speeds as with rotational
• Planets do not revolve at the same revolutional
  speeds around the sun

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Forces in Circular Motion

• Forces in Circular MotionCentripetal Force
• Force toward the center from an object, holding
  it in circular motion
• At right angle to the path of motion, not along
  its distance, therefore does NO work on object
• Examples
• Gravitation between earth and moon
• Electromagnetic force between protons and
  electrons in an atom
• Friction on the tires of a car rounding a curve

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Forces in Circular Motion

• Centrifugal Force
• Not a true force, but really the result of
  inertia
• Centrifugal force effect makes a rotating
  object fly off in straight line if centripetal
  force fails

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Forces in Circular Motion

• Centrifugal Force Can Mimic Gravity
• Bug in a can-can pushes up on bug due to
  centripetal force
• Bug pushes down on can due to inertia
• Space station could simulate gravity by rotation
  in same manner
• Rotational speed to simulate gravity depends on
  radius of the station
• 1 RPM would require 1 kilometer radius
• People have difficulty adjusting to rotational
  speeds over 2 RPM
• Stations would have to be large to compensate for
  proper gravity

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Homework RQ 1,3,5,7,9,14 TE 1,5,10