1. How do you start the rotation of an object? How do you open an door? What did we learn about the best way to open a door? The most efficient way to open or close a door is to exert a force perpendicular to the axis of rotation and as far away from the hinge as possible.

2. Lever Arm: perpendicular distance from the axis of rotation to the point where the force is exerted Torque: measure of how effectively a force causes rotation Torque, τ, = F r sinϴ where F is the applied force, r is the lever arm, and ϴ is the angle between the force and the axis of rotation.

3. Where does this equation come from? F parallel = F cos ϴ F perpendicular = F sin ϴ and with τ we are only concerned with the perpendicular component of the applied force. F cos ϴ F sin ϴ ϴ F

4. Other examples of torque:

5. If torques are balanced, what happens? NOTHING!!!

6. What happens on a see-saw if the weights of the people on it are the same? What happens if the weights are different? How can 2 people of different weights make a see-saw work?