1. WORK AND ENERGY Energy can be changed from one form to another. In any change the total amount of energy before a change is always equal to the total amount after the change. Gravitational Potential Energy Water behind a dam A skier at the top of a mountain

4. WORK AND ENERGY Energy can be changed from one form to another. In any change the total amount of energy before a change is always equal to the total amount after the change. Principle of conservation of energy: Energy can not be created or destroyed. Gravitational Potential EnergyA skier at the top of a mountain Kinetic Energy Thermal energy

5. Eg1: Pushing a book across a table against friction: 5N Workdone = F x s = 5N x 1m = 5J [ 1Nm = 1Joule ] Work is done on an object when a force acting on it makes it move: Work done = Force x displacement in the direction of the force  W = F x s cos  (J) (N) (m)

6. Eg2: Lifting a load against gravity Eg3 : No work is done

7. 1 2 Energy: When you do work on a system, its energy increases. Eg compressing a spring (see graph 1 ). So Energy transferred = workdone = ½ F x extension

8. When sailing, the wind often exerts a force F on the sails with a small component in the forward direction ( and a large sideways force). s If the boat moves forward a distance s the work done by the wind on the boat = F s cos .