Topic Overview

1. Topic Overview CLASSICAL MECHANICS Kinematics Motion without looking at its cause HOW? Dynamics & Statics Motion and its causes WHY & WHAT? Energy Just how much of it can you make? F Ff Ignore Forces

3. Learning Objectives • By the end of the lesson, you should be able to: • Describe the types of energy such as kinetic energy, elastic potential energy, gravitational potential energy, chemical potential energy • State the principle of the conservation of energy

4. What keeps the Man of Steel going? Just how much can he take? Can he go on forever without it? Does he ever run out of it? What is “it”?

5. What keeps the Man of Steel going? Yes, indeed, it is the Sun! The Sun’s Energy is what keeps him going! (So he is somewhat like a plant!)

6. What keeps the Man of Steel going? Energy is what allows Superman to exert forces. Every time he exerts a force to carry Lana Lang, he uses Energy. … the Energy he has is finite. If he depletes it, he will no longer be able to exert forces.

7. What is Energy? • Thus, Energy is the ability to do work. • Synonymous to: • The potential to perform a task. • The capacity to execute a process. Superman’s Energy Bar

8. What is Energy? Is Energy a Vector or a Scalar quantity? YES! It is a Scalar Quantity. It is measured in joules (J).

9. Different Forms of Energy • Just as Forces are of different nature, Energy may take different forms: • Kinetic Energy • Gravitational Potential Energy • Elastic Potential Energy • Chemical Potential Energy • Light Energy • Sound Energy • Thermal Energy • Electrical Energy H2O H2O H2O

10. Principle of Conservation of Energy The total amount of energy in an isolated system is ALWAYS conserved. Consequently, you cannot create more energy than there already is in the system. Neither can you destroy energy and make the sum total amount lesser. Energy cannot be created or destroyed, but may only be transformed from one form to another.

11. Principle of Conservation of Energy Maximum Gravitational Potential Energy 0 J of Kinetic Energy with respect to the reference line. 0 J in Gravitational Potential Energy Maximum Kinetic Energy with respect to the reference line.

12. Learning Objectives • You should now be able to: • Describe the types of energy such as kinetic energy, elastic potential energy, gravitational potential energy, chemical potential energy • State the principle of the conservation of energy Watch Animation: http://www.brainpop.com/science/energy/formsofenergy/

13. Revisiting Principle of Conservation of Energy • Can you state the Principle of Conservation of Energy? • What are the 2 consequences of CoE? • How can Peter Parker swing higher? By coe, this would mean that I cannot swing from one building to another of a greater height… Or could i? Ah! Yes… I need to kick off another building to gain an initial velocity!

14. Learning Objectives • By the end of the lesson, you should be able to: • Understand the relation between work done and energy change • Recall and apply the relationship work done = magnitude of a force x the distance moved in the direction of the force • State that kinetic energy = ½ mv2 (if time permits) and gravitational potential energy = mgh (for potential energy changes near the Earth’s surface)

15. How Much Work is Peter Parker doing? • Can you recall what is the definition of Energy? • Energy is the ability to do work. • But… What is “WORK”? Work done by a constant force on a fixed mass is the product of the magnitude of the force and the distance moved in the direction of the force. Work Done = F X d Wah! So cheem… Aiyah… WORK DONE is the transfer of energy lah… OR WORK is transferred energy

16. Calculating Work Done Hence, by the definition of work done, if peter moves a wooden block with a force of F, over a distance of d, in the same direction as the force, then the amount of work done is F x d. Force f exerted by peter Distance, d

17. Calculating Work Done How much work was done by Spidey? What is the energy conversion that is taking place? Force f = 10.0 N Notice that work is done AGAINST friction. In this situation, the body does not accelerate, it does not gain more KE as distance increaes. Friction = 10.0 n d = 40 m

18. Calculating Work Done How much work was done by Spidey? How much work was done against friction? Did the rest of the work that spidey do go to waste? Force f = 10.0 N Friction = 5.0 n d = 40 m

19. Calculating Work Done Spiderman carries Aunt May and lifts her off the ground with his arm strength YES! Superman is skiving. He has done NO WORK! Superman carries a durian and flies through vacuum. Who is skiving? Distance, d Distance, d

20. Calculating Work Done wall In which scenario is work being done? Or not done? FLOOR with FRICTION

21. Calculating Work Done against Gravity Work is done by the force in spidey’s arm muscles against gravity. Assume he moves up at a constant velocity… … F Work done = F X d If velocity is constant, Work done = W X h But W = mg Work done against gravity by Spidey = Potential Energy gained by Aunt May = GPE = mgh Watch simulation HEIGHT, h W

22. Block on Inclines Today, my friends (or fiends), carnage and venom are joining me for a block-moving competition. Rarrr! If we move the blocks with the same force but on different slope angles… HEHEHE… And push it ALL the way along the slopes until we are all at the same height above the ground… hehehe So who is doing more work? RARRRR! Who is going to expend more energy (ie. Do more work)?

23. Kinetic Energy The kinetic energy a moving body possess is given by KE = ½mv2 http://www.ac.wwu.edu/~vawter/PhysicsNet/QTMovies/Work-Power/WorkComparsionMain.html

24. Learning Objectives • You should be able to: • Understand the relation between work done and energy change • Recall and apply the relationship work done = magnitude of a force x the distance moved in the direction of the force • State that kinetic energy = ½ mv2 (if time permits) and gravitational potential energy = mgh (for potential energy changes near the Earth’s surface)