TorqueTorque

Give me a lever long enough and a fulcrum on which to

place it, and I shall move the world.

-Archimedes

Changing Circular MotionChanging Circular Motion In uniform circular motion, a point mass In uniform circular motion, a point mass

rotates around an external axis of radius, r. rotates around an external axis of radius, r. (Ex a person on a merry-go-round, a sock in (Ex a person on a merry-go-round, a sock in a washing machine)a washing machine)

A rigid rotating object is a mass that rotates A rigid rotating object is a mass that rotates around its OWN internal axis. (Ex a merry-around its OWN internal axis. (Ex a merry-go-round platform, a revolving door).go-round platform, a revolving door).

To open a door, you apply a force at a To open a door, you apply a force at a distance from the hinges and perpendicular distance from the hinges and perpendicular to the door.to the door.

Torque and forceTorque and force TorqueTorque is a new action created by is a new action created by

forces that are applied off-center to an forces that are applied off-center to an object. object.

Torque is what causes objects to Torque is what causes objects to rotaterotate or spin. or spin.

Torque is the rotational equivalent of Torque is the rotational equivalent of force. If force is a force. If force is a push push oror pull pull, you , you should think of torque as a should think of torque as a twisttwist. .

Calculating torqueCalculating torque The torque created by a force depends The torque created by a force depends

on the strength of the force and also on on the strength of the force and also on the lever arm. the lever arm.

The The lever armlever arm is the perpendicular is the perpendicular distance between the line of action of distance between the line of action of the force and the axis of rotation. the force and the axis of rotation.

Torque is calculated by multiplying the Torque is calculated by multiplying the force and the lever armforce and the lever arm

How torque and force differHow torque and force differ Torque is created by force but is Torque is created by force but is

not the same thing as force. not the same thing as force.

Torque depends on both force Torque depends on both force and distance. and distance.

Torque (N·m) has different units Torque (N·m) has different units from force (N). from force (N).

The same force can produce The same force can produce anyany amount of torque (including amount of torque (including zero) depending on where it is zero) depending on where it is applied. applied.

Calculating the lever armCalculating the lever arm Rotational equilibrium can also Rotational equilibrium can also

be used to find the lever arm be used to find the lever arm needed to make two different needed to make two different forces balances. forces balances.

A cat and boy can balance on a A cat and boy can balance on a see-saw even though their see-saw even though their weights are very different. weights are very different.

To solve this problem, figure out To solve this problem, figure out the lever arm needed for the the lever arm needed for the boy’s torque to balance the boy’s torque to balance the cat’s torque. cat’s torque.

The cat’s torque is 100 N-m, so The cat’s torque is 100 N-m, so the boy must sit 0.2 meters the boy must sit 0.2 meters from the fulcrum.from the fulcrum.