Circular Motion

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Circular Motion
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Objectives and Vocabulary

• Objectives
• Distinguish between rotation and revolution.
• Calculate angular speed.
• Explain how angular speed, linear speed, and
  distance are related.

• Vocabulary
• circular motion
• revolve
• angular speed
• linear speed
• circumference

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Rotations and Revolutions

• Both going around in a circle
• If the axis of rotation is within the object, it
  is called rotation
• record player
• ice skater spinning
• If the axis of rotation is external to the
  object, it is called a revolution
• earth going around the sun

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Rotational (Angular) Speed

• Number of rotations in a certain time.
• Revolutions/second
• Revolutions/minute (rpm)
• Period (T) time to make one revolution
• generally in seconds

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Linear Speed

• Distance traveled in a time period
• In circular motion, it is the circumference (2 p
  r) divided by the time to make one revolution.
• V (2 p r) / T

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Comparing Linear and Rotational Speeds
Red and blue have the same rotational speed
Blue has twice the linear speed
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Circular motion

• When an object travels in a circle, at any
  moment, the velocity is tangent to the circle.
• The direction of the velocity keeps changing even
  though the speed is constant.
• Since the objects velocity is changing, it must
  be accelerating.

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Velocity and Acceleration in Circular Motion
http//www.physicsclassroom.com/mmedia/circmot/ucm
.cfm
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Relationship between v and a
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What happens to the rock when the string breaks?
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Centripetal force

• Force that accelerates objects toward the center
  when they are in circular motion.
• Even though the velocity is tangent to the
  circle, the acceleration is toward the center.
• Centripetal acceleration v2/r
• Centripetal force mv2/r
• v is linear velocity
• spinning cork.

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Neat Circular Motion Ideas

• Artificial Gravity
• A spinning wheel in space will result in a kind
  of artificial gravity
• Angular Momentum
• Spinning ice skater
• Stability of bicycle wheel