1. Energy

2. Monday, 21 March 2016 Objective: –Identify the different forms of energy –Explain work and power

3. Energy Energy is the capacity to do work COPY

4. Feynmann Definition 'There is a fact, or if you wish a law, governing all natural phenomena that are known to date. There is no exception to this law - it is exact so far as is known. The law is called conservation of energy. It says that there is a certain quantity, which we call energy, that does not change in the manifold changes which nature undergoes. That is a most abstract idea, because it is a mathematical principle; it says that there is a numerical quantity, which does not change when something happens. It is not a description of a mechanism, or anything concrete; it is just a strange fact that we can calculate some number and when we finish watching nature go through her tricks and calculate the number again, it is the same.' –(R.P. Feynman, Tbe Feynman Lectures on Physics Volumes 1-3)

5. In other words… Energy is not a physically measurable quantity but rather a mathematical idea.

6. Energy There are two types of energy forms. One is active energy, the other is potential energy. Active energy is energy that has effects that are easily seen or detected. Potential energy is energy that is stored and only have effect when released. COPY

7. Types of energy Active energyPotential energy Kinetic EnergyChemical potential energy Solar energyElastic potential energy Electrical energyGravitational potential energy Sound energyNuclear energy COPY

8. Some meanings… Kinetic energy –The energy of an object when it is moving Chemical potential energy –Energy released by chemical reactions, eg from food, fuels and explosives COPY

9. More meanings… Elastic potential energy –Energy stored when a spring or rubber band is stretched or compressed COPY

10. More meanings… Gravitational potential energy –The energy an object gains when it is lifted up. This energy is released when it falls down again. COPY

11. More meanings… Nuclear Energy –Energy released in nuclear reactors or atomic bomb explosions. Solar energy is also produced from nuclear energy in the sun. COPY

12. Measuring Energy Energy is measured in Joules (J), or Kilojoules (kJ). 1000J= 1kJ COPY

13. Kinetic e.g. moving objects Kinetic

14. Sound e.g. music Kinetic

15. Chemical Potential e.g. batteries, food Potential

16. Heat e.g. hot stuff Kinetic

17. Light e.g. traffic lights Kinetic

18. Elastic Potential e.g. spring Potential

19. Nuclear e.g. atomic bomb, inside the sun Potential

20. Gravitational Potential e.g. object held high Potential

21. Electric Potential e.g. electricity Potential

22. Magnetic Potential e.g. magnets Potential

23. Calculating Energy Ep=mgh Gravitational potential energy = mass x gravity x height Ek=1/2mv 2 Kinetic energy = 1/2 x mass x velocity squared COPY

24. Energy Conservation Energy cannot be created or destroyed. It can only be changed from one form to another COPY

25. For example… When climbing on a diving board… –You use your chemical potential energy and turn it into kinetic energy as you move –The kinetic energy become gravitational potential energy when you are off the ground –When you dive your gravitational potential energy is transformed into kinetic energy again. –The kinetic energy is turned into heat and sound.

26. Energy Interactive Cloze

27. Work Work is done when a force moves an object. If work is done to an object then the object gains energy. The energy gained equals the work done. So… Both work and energy are measured in joules COPY

28. Calculating work done Work = Force x Distance W=Fd Where –W is the work in Joules –F is the force in Newtons which moves the object –d is the distance the object moves in metres COPY

29. Calculating work W dF COPY

30. Write the formula for… W= F= d=

31. An example question A toy car is pushed 2 m. The work done on the car is 800J. Calculate the size of the force which moved it. –d= 2m –W=800J –F=? F=W/d =800/2 =400N COPY

32. Power Power is the rate at which work is done. Power is measured in watts, W

33. Power Power is calculated using: Power= Work done Time taken P=W/t

34. Sample Problem (power) A runner can do 12000J of work in one minute. What is the power output? W= 12000J t=60s P=? P=W/t P=12000/60 P=200W