Chapter 11 Rotational Mechanics
Torque
If you want to make an object move, apply a force. If you want to make an object rotate, apply a torque.
Torque = force x lever arm distance
Example: 80 N
3 m
(80 N) x (3 m) = 240 N*m
Lever Arm
The lever arm distance is the distance from the fulcrum to a point perpendicular to the applied force.
Examples of Lever Arms
Find the lever arm in the following examples:
Torque = force x lever arm distance
• Balancing Torques
Larger kid sits closer to fulcrum to balance torque
Inertia
• For objects at rest or in motion, they will tend to stay at rest or in motion unless acted on by an outside force
• Inertia is the tendency of an object to resist a change in its motion
• Inertia is dependent upon mass.
Rotational Inertia
• The same is true for rotating objects:
• Rotational Inertia – tendency of an object to resist a change in rotation
Moment of Inertia: The resistance of an object to changes in its rotational motion
Moment of intertia = (mass)(radius)2
I = mr2
Angular Momentum• Just as an object moving in a straight path has linear momentum, a rotating object has angular momentum.
• angular momentum = rotational inertia x rotational velocity
Angular momentum = I x ω
Angular Momentum: The measure of how difficult it is to stop a rotating object
Angular Momentum = (mass)(velocity)(radius)
L = mvr
Law of Conservation of Angular Momentum:
If no unbalanced external torque acts on a rotating system, the angular momentum of that system is constant.