Chasing your tail for science.

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Chasing your tail for science.
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Moving

• Stand up.
• Walk in a perfectly round path to your left.
• Which way do you have to push with your foot to
  walk in the circle?
• Answer
• Toward the center of your path.

3
Pushing

• Using the ball at the front of the room.
• Make the ball travel counterclockwise in a circle
  around a pen at the lab tables.
• Which way do you have to push to get the ball to
  go in a circle?
• Answer
• Toward the pen.

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Circular motion

• You have just studied circular motion.
• It has 2 dimensions.
• Speed can be constant but velocity will always
  change.
• Moving in a circle causes velocity to constantly
  change.
• But which way?
• Lets study!!!!!!!!!!!!!!!!!!!!!!!!

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Vocab

• Circumference
• distance around a circle.
• C 2?r Units meters (m)
• Period
• time to complete one revolution along a circular
  or repeating path.
• Symbol T Unit seconds (s)
• Frequency
• number of rotations per second.
• Symbol f Unit Hertz (Hz)

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Calculate speed

• To find speed, need to know distance and time.
• Time for once around is the period, T
• Distance for once around is circumference.
  C2pr
• So,
• Units are m/s
• This is when moving at a constant speed.

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Speed calculation

• A merry-go-round has a radius of 6.0 m and takes
  60 s to complete one revolution.
• How fast is an ant traveling that is sitting at
  the outer edge of the merry-go-round?
• Give T 60 s, r 6.0m
• v 0.628 m/s

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Acceleration?

• What happens to the velocity vector as you move
  in a circle?
• It changes direction. You have zero displacement
  for each round trip.
• Changing velocity means, acceleration.

• Which way is it changing?

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Acceleration

• Velocity changes toward the center.
• Acceleration points toward center of circular
  path.
• Called Centripetal Acceleration
• Always toward center of curved path for constant
  speed.

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Centripetal Acceleration

• Found by equation
• Where
• v speed
• r radius
• Acceleration depends on both speed and radius of
  path.

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Centripetal Acceleration

• Find acceleration for merry-go-round.
• v 0.628 m/s, r 6.0 m
• So ac (0.628 m/s)2/6.0m 0.066 m/s/s
• How would ac change if the velocity was constant
  and the ant
• Moved toward center?
• Acceleration will increase.
• Moved away from center?
• Acceleration will decrease.
• Moved to center?
• No acceleration. r 0

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True Force

• When you move in a circle, Which way are you
  accelerating?
• Toward the center.
• Which way are you being pushed?
• Toward the center.
• What object is doing this?
• The surface.
• What is the sum of the forces?

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Centripetal Force

• Unbalanced force responsible for circular motion.
• Always exerted toward center of path.
• There is no object pushing you outward.
• THERE IS NO CENTRIFUGAL FORCE EVER.
• What makes you feel the fake effect?
• Inertia.

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Centripetal Force

• Found by using 2nd Law.
• SFma
• SFcmac
• This is the total sum of the forces which causes
  circular motion.

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Example

• Find the centripetal force exerted on you when
  standing at the edge of the merry-go-round.
• ac 0.066m/s/s , m 50 kg
• SFcmac
• SFc(50 kg)(0.066 m/s/s) 3.3 N
• Which way is this force exerted?
• Toward Center of merry-go-round.

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Why dont I fall?

• Gravitron centripetal force exerted by the wall
  keeps you moving in a circle. Friction between
  body and wall balances the force exerted by Earth
  and you dont fall.
• Rollercoaster loop at top you do not fall
  because track pulls the cars toward center at g.