Circular Motion

1
Circular Motion

• Chapter 11

2
Revolution

• Motion about an external axis.
• A record turntable rotates
• A bug sitting on the record revolves.

3
Rotational Motion

• Motion in a circle spin
• Motion about an internal axis.

4

• Particles in the rings of Saturn revolve around
  Saturn.
• Saturn spins on its axis, or rotates.

5
Tangential Speed

• Speed of an object traveling in a circle is
  sometimes called Tangential Speed because the
  direction of motion is always in a tangent to the
  circle.

6
Tangential Speed Calculation

• Speed distance/time
• When traveling in a circle, the total distance
  around the circle is the circumference.
• Circumference 2 pi radius
• The time it takes to complete one cycle or
  revolution is called the period (T).
• SO
• Tangential speed (2piradius)/T

7
Rotational Speed (angular speed)

• The number of rotations/unit of time.
• RPM rotations/min

8
Centripetal Force

• Centripetal force is a force that causes an
  object to travel in a circle.
• Centripetal means center-seeking.

9
What provides the centripetal force?

• Tension
• Gravity
• Friction
• Normal Force

Centripetal force is NOT a new force. It is just
a force that is required to keep an object moving
in a circle.
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10
Demonstration

• The object on the left travels freely based on
  its inertia, while the object on the right is
  forced to travel in a circle by the wooden block.
  Centripetal force is applied.

11
Friction

• Inertia should cause the car to continue in the
  direction in which it was traveling. What causes
  it to travel in a circular direction? What
  applies the centripetal force?

12
Gravity

• Gravity is the centripetal force that causes
  planets to revolve around the sun.

13
Calculating Centripetal Force
14
Centrifugal Force

• Centrifugal means Center-fleeing and it is a
  force that seems to push you outward.
• Think playground Merry-go-Round

15

• If you let go, youll be like Mary Poppins and
  fly off the Merry-go-Round.

16

• You do not fly straight outward.
• Instead you follow tangential motion, and
  continue in a straight line from the point where
  the circular motion ends.

17
Centrifugal Force

• What it really is is inertia.
• Inertia is NOT force, therefore, centrifugal
  force is not a real force.

18

• Some amusement parks have these. You get inside
  and the ride spins around its axis. You seem to
  be forced to stick to the wall as a result of
  this rotational motion.
• This is the
• centrifugal force
• Which is really
• Your inertia.

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Inertia, Centrifugal Force

• In a car.

20
In action