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					Ch. 11 Rotational Mechanics


            Torque
TORQUE
 Produced when a force is applied with
  leverage.
 Force produces acceleration.
 Torque produces rotation.
TORQUE
 Torque = Force X Lever Arm
 Force must be perpendicular to lever arm.
 Torque is increased by
    –   increasing force
    –   increasing length of lever arm
A torque is used when…
 Opening a door
 Turning on a faucet
 Tightening a bolt with a wrench
 Using a screwdriver
 Using a lever
Balancing Torques
 Torques are balanced when clockwise
  torque = counter-clockwise torque.
 A meter stick is balanced at its center and a
  20 N block is hung at the 80 cm mark.
  Another block is hung at the 10 cm mark.
  What is the weight of the 2nd block?
Toppling and Tumbling
 When the CG is not over the area of
  support, a torque is produced - toppling.
 When a force is applied at the CG, no
  torque is produced.
 When a force is applied off center, a torque
  is produced - tumbling
    –   Object will rotate about its CG.
ROTATIONAL INERTIA
 An object rotating about an axis tends to
  keep rotating about that axis.
 Rotational Inertia - the resistance of an
  object to changes in its rotational motion.
 It takes a force to change linear state of
  motion.
 It takes a torque to change rotational state of
  motion.
ROTATIONAL INERTIA
   Depends on mass and the distribution of the
    mass.
    –   The greater the dist. between the bulk of the
        mass of an object and the axis about which
        rotation takes place, the greater the rotational
        inertia.
   Long objects are harder to rotate than
    shorter objects
ROTATIONAL INERTIA
 Not necessarily a fixed quantity
 Can be changed by changing distribution of
  mass
    –   choke up on a bat
    –   bend legs
    –   holding an object
   The farther the mass from the axis, the
    greater the rotational inertia.

				
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posted:3/23/2011
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