2. Work, Energy and Power Energy (Joule) Ability to do work. Law of Conservation of Energy: Energy cannot be destroyed nor created but is converted from one form to another. Kinetic energy- Energy in motion = 1/2mv 2 Gravitational potential energy(GPE)= mass x gravity x height= mgh Energy stored in an object due to its position(height) in a gravitational field. Work (Nm or J) Product of force and distance moved in the direction of the force. W= F.s or Fs.cosƟ Power (W)

3. Work W = F s This formula applies when: the force is constant. the force is in the same direction as the displacement of the object F x  W = F s cos  This formula applies when the force is acting at an angle. First you find the horizontal force.

4. Zero Work How much work does this force do? Zero Zero work is done when distance moved is zero or a force is perpendicular to the distance moved. r v

5. Work, energy and power are all scalar quantities The crate requires energy to move from A to B AB The crate also requires energy to move back to A. In either way AB or BA the crate gains energy! Direction is not significant. The work done depends on the total distance moved and not displacement. It is a scalar quantity.

6. Work: Incline Example m  20 0 6.2m  k k F A box is being dragged by a force of 15N is applied at an angle 20 0 to the horizontal. Find the work done on the when the box moves 6.2 m

7. What is a Joule? Is the work done when a force of 1N is moved through 1m in the direction of the force. 1J = 1N x 1M = 1NM

8. Work done by gas= Pressure x change in Volume Work = f x d but F = P x A Work = P. A. X but A.X = change in volume Therefore: W = P Δ V Work done by expanding gas W= P Δ V=P(v 2 –V 1 )

9. An ideal gas is held in a container by a moveable piston and thermal energy is supplied to the gas such that it expands at a constant pressure of 1.2 × 10 5 Pa.The initial volume of the container is 0.050m 3 and after expansion the volume is 0.12m 3.Determine the work done by the gas. P = 1.2 × 10 5 Pa Δ V= 0.12-0.05=0.07 m 3 W= P Δ V 1.2 x 10 5 x 0.07=8400J.

10. Energy is the ability to do work. It is measured in Joules(J)

11. Types of Energy Electrical energy ACTIVE (KINETIC) ENERGY STORED (POTENTIAL) ENERGY

12. Kinetic Energy Kinetic energy is the energy of motion. By definition, kinetic energy is given by: K = ½ m v 2 The equation shows that...... the more kinetic energy it’s got. the more mass a body has or the faster it’s moving K.e is proportional to v 2, so doubling the speed quadruples kinetic energy, and tripling the speed makes it nine times greater.

13. Principle of Conservation of Energy It states that energy can neither be created nor destroyed but can only change forms. This means that all the energy in a system before and after is constant. a mass is dropped from some height. PE is converted into kinetic energy and heat generated due to friction with the air. Conservation of energy : mgh = ½ m v 2 + heat. m m after v heat

14. K.E to PE exchange Energy/J Time/s The graphs showing variation of KE and PE with time. Both graphs are smooth curves. Why?

15. Example 70kg Two 40kg and 70kg connected by a string passing are held as shown below. When released, Find the speed of the 70kg mass when it strikes the ground. 40kg 12m 5m

16. 15 Power is the rate at which work is done. Or rate of energy transfer Power = force x velocity=Fv Power The unit of power is Joules per(Js -1 ) or Watts(W).

17. Energy Efficiency Definition: The fraction(amount )of energy converted into useful energy. Efficiency = useful energy out total energy in It has no Units Calculate the efficiency of the bulb.

18. A Sankey Diagram – An arrow diagram showing the energy changes.The thickness of each arrow represents the amount of energy converted.