SECTION 6'2 CIRCULAR MOTION

1
SECTION 6.2 CIRCULAR MOTION

•  Objectives
• Explain why an object moving in a circle at a
  constant speed is accelerated.
• Describe how centripetal acceleration depends
  upon the objects speed and the radius of the
  circle.
• Identify the force that causes centripetal
  acceleration.

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INTRO

• Acceleration deals with a change in velocity
  (vector quantity thus magnitude and DIRECTION)
  divided by a change in time, thus something that
  is moving around in a circle at a constant speed
  has acceleration since the direction is changing.

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DESCRIBING CIRCULAR MOTION

• Uniform Circular Motion the movement of an
  object or particle trajectory at a constant speed
  around a circle with a fixed radius.
•  
• ?v ?d / ?t ?r / ?t
•  
• Tangent a straight line or plane that touches a
  curve or curved surface at a point but does not
  intersect it at that point 
•  
• As the velocity vector moves around the circle,
  its direction changes but its length remains the
  same.
•   ?a ?v / ?t
• Acceleration vector of an object in uniform
  circular motion always points toward the center
  of the circle. 

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DESCRIBING CIRCULAR MOTION

• Centripetal a quantity that always points
  toward the center of a circle center seeking it
  was originated by Sir Isaac Newton.
• Centripetal Acceleration the Center Seeking
  acceleration of an object moving in a circle at
  constant speed.

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CENTRIPETAL ACCELERATION

• Centripetal Acceleration the Center Seeking
  acceleration of an object moving in a circle at
  constant speed. It always points toward the
  center of the circle. Its magnitude is equal to
  the square of the speed divided by the radius of
  motion.
• ac v2 / r
•  
• Period the time needed for an object to make
  one complete revolution. It is denoted by T.
•  
• Velocity of an object traveling around a circle
  can be found by
• v 2?r / T

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CENTRIPETAL ACCELERATION

• And because of that we can find the Acceleration
  by
• ac 4?2r / T2
•  
• Centripetal Force the net force exerted toward
  the center of the circle that causes an object to
  have a centripetal acceleration. It is equal to
  the mass of the object times its centripetal
  acceleration.
• Fc mac

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CENTRIPETAL ACCELERATION

• Do Example Problem 2 p. 155
• ac 4?2r / T2 Then FT Fc mac
• ac 4?2(.93) / (1.18)2 FT
  .013(26.34)
• ac 36.68 / 1.3924 FT .342 N
• ac 26.34 m/s2
•  
• Do Practice Problems p. 156 12-15

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A NONEXISTENT FORCE

• Remember Newtons First Law states that an object
  at rest will stay at rest and an object in motion
  will stay in motion unless acted on by an outside
  force.
•  
• Go over example of the car and turning.
•  
• Centrifugal Force an outward force. It is
  fictitious. It does not exist.
• Do 6.2 Section Review p. 156 16-21