Work, Power & Energy?

1. What do you think of when you hear the words: Work, Power & Energy?

2. Work = Force|| x Distance W = Fd The distance is the displacement. Only the force parallel to the displacement does work

3. Work • Force MUST be applied in the direction of motion • The unit for work is the Newton-meter which is also called a Joule. • 1 joule is equal to a force of 1 N exerted over a distance of 1 m

4. Work or No Work

5. m= 10kg In this case, the weight does positive work d = 2 m Work = mgd = (100N)(2m) Work = 200 Nm =200J m= 10kg mg = 100N

6. FA m= 10kg In this case, the weight does negative work mg = 100N d = 2 m Fa Work = -mgd = -(100N)(2m) Work = -200 Nm = -200J m= 10kg mg = 100N

7. Power • measured in watts (W) • One watt of power is used when one joule of work is done in one second. http://www.cartoonstock.com/newscartoons/cartoonists/pto/lowres/pton114l.jpg

8. Power • Power is equal to the amount of work done per unit time. • The unit for power is the Joule/second which is also called a Watt.

9. What is horsepower? • 1 horsepower = 746 Watts • A horse exerting 1 horsepower can raise 330 pounds of coal 100 feet in a minute, or 33 pounds of coal 1,000 feet in one minute, or 1,000 pounds 33 feet in one minute.

10. Energy • Universe is made up of matter and energy. • Energy is the mover of matter. • Energy has several forms, some examples: • Mechanical • Kinetic • Potential • Electrical • Heat • Chemical http://tiki.oneworld.net/energy/energy.html

11. Mechanical Energy • Energy contained by an object due to its motion or its stored energy of position. • It can either be potential energy or kinetic energy. • All forms of energy are measured in joules (J). • ME= KE + PE

12. Conservation of Energy • Energy cannot be created nor destroyed • Energy may be transformed from one form into another, but the total amount of energy never changes. • So why worry about conserving energy? http://sol.sci.uop.edu/~jfalward/physics17/chapter3/chapter3.html

13. Conservation of Mechanical Energy • KE (before) + PE (before) = KE (after) + PE (after) • Why does a dropped ball not return to its original elevation? http://www.science-projects.com/Drop/DropBalls.htm

14. Energy Transformation of a Pendulum http://www.glenbrook.k12.il.us/gbssci/Phys/mmedia/energy/pe.html

15. Potential Energy • (PE) stored chemical energy or energy of position. • An object’s ability (potential) to do work by virtue of its position. • Types: elastic, gravitational and chemical. • Examples: • Rubber bands • Springs • Bows • Batteries • Gravity?

16. Gravitational Potential Energy • PE = Weight ´ height = Fwh = mgh • PE = m g h • Question: • How much potential energy does a 10kg mass have relative to the ground if it is 5 meter above the ground?

17. Potential Energy • The same work is done on each block.  What mattersis the final elevation, not thepath followed http://sol.sci.uop.edu/~jfalward/physics17/chapter3/chapter3.html

18. Kinetic Energy • The energy of motion. • Kinetic Energy = ½ mass ´ velocity2 KE= ½ mv²

19. How much work does gravity do on the falling mass? PE = mgh mg h h Work = mgh mg

20. How much energy does the mass have at the bottom of its fall, just before it hits the ground? PE = mgh mg h h Kinetic energy mg v

21. PE = mgh If potential energy at top of path is 100 J, how much kinetic energy does the ball have just before it hits the ground and comes to a stop? mg h KE = ½ mv2 mg v

22. Check for Understanding Determine the kinetic energy of a 1000-kg roller coaster car that is moving with a speed of 20.0 m/s.

23. Determine the Unknown Information:

24. More Energy Transfer • High speed winds are used to do work on the blades of a turbine at the so-called wind farm. • Mechinacal Energy from the air gives the air particles the ability to apply a force to the blades. • As the blades spin, their energy is converted into electrical energy (a non-mechanical form of energy) and supplied to homes and industries in order to run electrical appliances.

25. Energy Transfer... • This diagram shows that the potential energy of the boy is changing as he swings. • Explain what is happening, in other words how is the energy changing?

27. Mechanical Energy Conversion • Explain the following diagram: • What is happening • Explain the conversion of KE to PE to KE to PE… • http://www.funderstanding.com/coaster

28. Work/Energy Relationship • If you want to move something, you have to do work. • The work done is equal (ideally) to the change in kinetic energy. • what is ideal? is this actual? • W = DKE http://sol.sci.uop.edu/~jfalward/physics17/chapter3/chapter3.html

29. Work-Energy Relationship • What happens to your stopping distance when you… • Double your speed? • Triple your speed? http://www.thegrid.co.uk/index_files/Mickel-crash-brands.jpg

30. Joule to Joule http://www.glenbrook.k12.il.us/gbssci/Phys/mmedia/energy/cs.html

31. Truck Collision • In a head-on collision: • Which truck will experience the greatest force? • Which truck will experience the greatest change in velocity? • Which truck will experience the greatest acceleration? • Which truck would you rather be in during the collision? WHY? http://hyperphysics.phy-astr.gsu.edu/hbase/truckc.html#c1

32. Imagine standing on your desk…if you jumped off, how fast would you be moving just prior to reaching the floor? • How much work would you do on the floor? • What information do you need to know? • G • U • E • S • S http://school.discoveryeducation.com/clipart/images/in-desk.gif