# Ch Rotational Mechanics by sanmelody

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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
 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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