Circular Motion: Centripetal force

1
Circular MotionCentripetal force

• Chapter 9 Nov 7/8

2
Objectives

• Develop examples of centripetal force
• Describe the motion of an object if the
  centripetal force acting on it ceases

3
Read section 9.2 on page 123

• Facts
• The linear component of something moving in a
  circle.
• Number of circles something makes in a certain
  amount of time

• Topic
• What is tangential speed?
• What is rotational speed?

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Difference between Tangential and Rotational
speed

• Facts
• Depends on the circles radius
• Larger radius more speed
• Smaller radius less speed
• Does not depend on radius/distance
• Same no matter where on circle

• Topic
• Tangential Speed
• Rotational speed

5
Study Figure 9.3 on page 124

• Draw the figure below

• Explain the figure with rotational speed and
  tangential speed

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Check for Understanding

• Facts
• Outside horse (larger radius)
• The outside horse
• 5m/s
• 2 RPM because rotational speed is not affected by
  radius/distance

• Topic
• Which has a greater tangential (linear) speed
  travels faster on a merry-go-round, a horse on
  the outside or one near the center.
• Who will fall off the ride faster?
• The tangential speed at the outer rim of a Ferris
  wheel is 10 m/s. What is the tangential speed of
  a position half way from the center to the outer
  rim?
• You sit at the outer rim of a Ferris wheel that
  rotates at 2 revolutions per minute (RPM). What
  would your rotational speed be if you were
  instead clinging to a position halfway from the
  center to the outer rim?

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What makes objectives move in a circle?

• Topic
• Centripetal force

• Facts
• Means center-seeking
• Any force that causes an object to follow a
  circular path
• Example gravity pulls all of us to the center of
  the Earth
• Units are Newtons (N)
• Symbol is Fc
• Centripetal force mass x centripetal
  acceleration
• Fc mac or Fc mv2
• r
• because ac v2
• r

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Teacher DemonstrationCentripetal force and
tangential speed

• Topic
• Why does the cup move in a circle?
• What will happen if I let the cup go?

• Facts
• Centripetal force pulls inward (from my hand)
  while tangential speed acts at each point
  resulting in the circle.
• The cup will fly in a straight line from the
  point the centripetal force stops

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Check for Understanding

• Topic
• What would happen if the force of gravity
  suddenly stopped acting on the planets?

• Facts
• They would fly off tangent in space, rather than
  continue their orbit

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Closing

• Topic
• Why do objects move in a circle? Include the
  following terms in your explanation.
• Centripetal force
• Tangential speed

• Facts

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Homework

• Read Chapter 12
• This material is difficult to understand, but
  write notes and questions
• This will be checked for a HW grade
• It will also help you understand the next lesson