1. Physics Section 7.4 Calculate the torque generated by a force.
Torque is a quantity that measures the ability of a force to rotate an object around an axis.
A lever arm is the perpendicular distance from the axis of rotation to a line drawn along the direction of the force.
Torque is the product of a force applied perpendicular to the lever arm and the length of the lever arm.
Torque = force x lever arm T = F∙d
The units of torque are the N∙m.

2. Torque:Τ= F∙d sinθ T = torque (Nm) F = force (N) d = lever arm (m) θ = angle between the force and the lever arm
Torque is a vector. The direction is either clockwise or counter-clockwise.
Example: A force of 75 N is applied perpendicular upward to a lever with a length of 2.1 m. Find the torque produced.

3. Example Find the total torque generated.

4. A machine is a device that increases force by increasing the distance the force is applied.
Simple machines
1. lever
2. inclined plane A small force is applied over
3. wheel and axle a large distance. A large
4. wedge force is the output over a
5. pulley small distance.
6. screw

5. Mechanical Advantage = output force input force
MA = Fout = din
Fin dout

6. Example
A person pushes a 1200 N box up an incline by using a force of 400 N. Find its mechanical advantage.

7. Efficiency = Wout = (Fout)(dout) Win (Fin)(din)
The work put into a machine will equal the work output, if there is no friction. Most machines have friction.
The efficiency of a machine is the ratio of the work output to the work input.
Efficiency = Wout = (Fout)(dout)
Win (Fin)(din)
The efficiency of a machine is 65%. A force of 82 N is applied over a distance of 6.5m. What force is output over a distance of 2.3m?

8. assignment
Page 261
Problems 1-3, 5-8