1. Unit Two: Mechanical Energy A: Work- –in everyday life, it means many things –In physics, work is “what is accomplished when a force acts on an object that moves” or the measure of a job done

2. Work is the product of an applied force and the displacement of an object in the direction of the applied force Equation: W= where- F= applied force and d= displacement Units= N*m which is a.k.a a Joule (J)

3. Examples 1. When you push a wall, no work is done because the wall does not move 2. When we lift a load against the Earth’s gravity, work is done –The heavier the load the more work that is done

4. Situations where work is not done 1. There is a force but no displacement (i.e pushing on a wall) 2.A. The force is perpendicular to the displacement (i.e walking forward while carrying books) B. Satellites orbiting the earth 3. An object moves without an applied force (skating on ice)

5. Word Problems 1.If a person pushes a car with a force of 800N for a displacement of 30m, how much work was done? 2.Find the work required to lift 3.0 x 10 7 to a height of 5.0m?

6. Positive work is done when the applied force and the displacement act in the same direction. When the weight is raised above his head, the displacement and the applied force are in the same direction.

7. Example: If the total mass of the barbell and the weight is 135 kg, and he raises the barbell a distance of 65 cm above his chest with a constant velocity what is the work done on the barbell by the weight lifter?

8. Negative work is done when the applied force is still upward; however the displacement is opposite in direction. When the weight is lowered, the applied force is the same upward direction; however the displacement is opposite in direction.

10. Sample Problem A box that weighs 200 N is lifted a distance of 0.5 m straight up. How much work is done? To lift a box of 200 N upward requires you to apply an upward force of 200 N. If this box must be lifted 0.5 m upward, then the displacement would be 0.5 m [up]. Note: the applied force and the displacement are in the same direction.

11. In some cases, the force and displacement moved are not in the same direction: –

12. –*consider the component of force parallel to the direction in which the object moves –To find this, use W=Fd*cos Θ

13. Example –A child pulls a wagon by exerting a force of 20N at an angle of 30 o to the horizontal. If the child pulls it 100m along the ground, calculate the work done.

14. Answer