Circular motion

1
Circular motion

• Rotation or spin around an axis
• spin or rotation is around an internal axis
• a record or cd
• Revolution when an object turns about an
  external axis. Earth around the sun is revolution

2
Centripetal force

• Any force that causes an object to follow a
  circular path
• Center seeking force
• Gravitational force direct towards the center of
  the earth
• Electrons are attracted towards the center of the
  nucleus

3
Centrifugal force

• Center fleeing or away from the center
• When we twirl a can we feel a force on the
  string, what is this force?
• If we let go of the swinging can how does it go?

4
Tangential speed

• The speed tangential to the circle
• If the gravity was turned off the
  direction and speed of the earth at that instant
• Rotationtal speed (angular speed) rpm

5
Calculate tangential speed

• Tangential velocity rpm times the circumference
  
• Watch the units change to seconds

6
(No Transcript)
7
Given the mass, radius and rpm what is the force
8
Torque

• Torque is the Perpendicular force times the
  lever arm

9
In a washing machine

• On spin cycle how does the water get removed?
• Why would we rotate a space station?

10
Why does the earth still spin
11
Momentum is of two kinds, angular and linear. 
12
Angular momentum

• Angular momentum is the tendency of a rotating
  object to keep rotating at the same speed about
  the same axis of rotation. 
• angular velocity (symbol w), measured in radians
  per second (a radian is about 1/6 of a full
  circle -- there are 2p radians in a full
  circle). 

13

• the magnitude of the angular momentum in this
  case is L mvr, where L is the angular momentum,
  m is the mass of the small object, v is the
  magnitude of its velocity, and r is the
  separation between the objects

14
Angular momentum (spin)

• Angular momentum is conserved
• Why do you go faster when you pull in arms?

15
Calculate angular momentum