Ch. 11 Rotational Mechanics
Produced when a force is applied with
Force produces acceleration.
Torque produces rotation.
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
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.
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
It takes a torque to change rotational state of
Depends on mass and the distribution of the
– 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
Long objects are harder to rotate than
Not necessarily a fixed quantity
Can be changed by changing distribution of
– choke up on a bat
– bend legs
– holding an object
The farther the mass from the axis, the
greater the rotational inertia.