Work and Energy

1. Work and Energy PowerPoint notes and practice problems

2. When do we do “work”? • Two conditions must be met for work to be done • The application of a force, and • The movement of something by that force in the direction of the force applied • When we lift a load against Earth’s gravity • The heavier the load or • The higher we lift it the more work we do

3. WORK Work = Force x distance W = Fd Joule is the unit for work. Something must be moving in order for work to occur.

4. Calculating work • How much work is done if a box of books is pushed 10 meters across the floor with a force of 25 Newtons? 2. How much work is done if a barbell is lifted 1 meter off the floor using a force of 10 Newtons?

5. Calculating work • How much work is done if a box of books with a mass of 50 kg is pushed 10 meters across the floor at 1 m/s? • F = ma • W = Fd

6. Calculating work • W = Fd W = 25N x 10m = 250N·m or 250J • W = Fd W = 10N x 1m = 10N·m or 10J • F = ma ; F = 50kg x 1m/s = 50N W = Fd W = 50N · 10m = 500N·m or 500J

7. Power • Power is the rate at which work is done. It equals the amount of work done divided by the time interval during which the work is done. The unit of power is joule per second, known as the watt. One watt of power is used when one joule of work is done in one second W • work done power = power = t • time interval

8. Calculating work • If a box of books with a mass of 50 kg is pushed 10 meters across the floor at 1 m/s, how much power was used to push the box? • F = ma • W = Fd • P = W/t

9. Calculating work • F = ma; F = 50kg x 1 m/s = 50N W = Fd; W = 50N x 10m = 500J P = W/t = 500J /10s = 50J/s or 50W

10. ENERGY • Fundamental building blocks of our universe. • Appears in different forms • Has the ability to do work • Any object that has energy has the ability to create force. • Units are measured, like work, in joules (J)

11. Mechanical Energy • Mechanical Energy is the energy due to the position of an object or the movement of an object • Mechanical Energy = Potential Energy + Kinetic Energy • ME = PE + KE

12. POTENTIAL ENERGY • Comes from the position of an object relative to earth. • Stored energy • Amount of potential energy must be the same as the amount of work done to lift the object against gravity. • Objects do not use potential energy until they move.

13. POTENTIAL ENERGY • Usually referred to as gravitational potential energy gravitational potential energy = weight x height

14. Potential Energy Formula 9.8m/s2 PE = mgh height Potential energy mass In the last unit we learned that W = mg PE = Wh height Potential energy weight

15. Calculating Potential Energy • What is the PE of a boulder that weighs 100N sitting on a ledge 2m above the ground? • What is the PE of a 4N can of paint at the top of a 10 meter ladder? • If the limb of a tree has a PE of 90J in its present position 15 meters above the ground, what is it’s weight? What is the limbs mass?

16. Calculating Potential Energy • PE = Wh PE = 100N x 2m = 200J • PE = Wh PE = 4N x 10m = 40J • PE = Wh 90J = W x 15m = 90J/15m = 6N W = mg; 6N = m x 9.8m/s2 = .61 kg

17. KINETIC ENERGY • Energy in motion • Energy depends on Speed & Mass • Speed increases - KE increases • Mass increases - KE increases

18. Kinetic Energy Formula • Kinetic energy = ½ mass x speed2 • KE = ½mv2 • When working this formula, always square speed first. speed Kinetic energy mass

19. Kinetic Energy Formula • Kinetic energy is also equal to the net force operating on an object and the distance it travels or Net force x distance = kinetic energy Fd = kinetic energy • Now if KE = Fd and if KE = ½mv2, then Fd = ½mv2

20. Calculating Kinetic Energy • A ball with a mass of .15 kg is thrown at a speed of 40.2 m/s. What is the ball’s KE? • If a car with a mass of 2000 kg is moving at a speed of 25 m/s, what is it’s KE? • If a force of 1145N is applied to a railroad boxcar and it rolls a distance of 85 meters, what is it’s KE?

21. Calculating Kinetic Energy • KE = ½mv2 = (.5 x .15kg) x 40.2 m/s2 KE = .075kg x 1616.04 m/s = 121.2J • KE = ½mv2 = (.5 x 2000kg) x 25 m/s2 KE = 1000kg x 625 m/s = 625000J • KE = Fd = 1145N x 85m = 97325J

22. LAW OF CONSERVATION OF ENERGY Nature never creates or destroys energy; energy only gets converted (changed) from one form to another.

23. Energy Transformation PE PE KE KE Energy will continually transfer between forms.

24. KE to PE • PE and KE are always equal to the total amount of energy • PE and KE are in an inverse relationship – as one increases the other decreases

26. Calculate the PE and the KE

27. Continual transfer between forms… • Mechanical Energy • Radiant (Electromagnetic) Energy • Electrical Energy • Chemical Energy • Nuclear Energy • Thermal Energy

29. TYPES OF ENERGY Mechanical, Electromagnetic, Electrical, Nuclear, Chemical and Thermal

30. Energy due to a object’s motion (kinetic) or position (potential). The bowling ball has mechanical energy. When the ball strikes the pins, mechanical energy is transferred to the pins! What is Mechanical Energy?

31. Examples of Mechanical Energy

32. Light energy Includes energy from gamma rays, xrays, ultraviolet rays, visible light, infrared rays, microwave and radio bands What is ElectromagneticEnergy?

33. Energy caused by the movement of electrons Easily transported through power lines and circuits and converted into other forms of energy What is Electrical Energy?

34. Energy that is available for release from chemical reactions. The chemical bonds in a matchstick store energy that is transformed into thermal energy when the match is struck. What is Chemical Energy?

35. Examples of Chemical Energy

36. Heat energy The heat energy of an object determines how active its atoms are. A hot object is one whose atoms and molecules are excited and show rapid movement. A cooler object's molecules and atoms will show less movement. What is Thermal Energy?

37. QUIZ TIME! • What type of energy cooks food in a microwave oven? 2. What type of energy is the spinning plate inside of a microwave oven?

38. QUIZ TIME! Electrical energy is transported to your house through power lines. 3. When you plug an electric fan to a power outlet, electrical energy is transformed into what type of energy?

39. QUIZ TIME! 4. What energy transformation occurs when an electric lamp is turned on?

40. 5. What types of energy are shown below?

41. 6. What type of energy transformation is shown below?

42. 7. What types of energy are shown below?

43. 8. What type of energy is shown below?

44. 9. What type of energy conversion is shown below?

45. 50 point bonus question • Draw a flow map showing the flow of energy transformations in a car from starting the vehicle to driving. You should have 5 different types of energy transformations.

46. QUIZ TIME! 1. What type of energy cooks food in a microwave oven? ELECTROMAGNETIC ENERGY 2. What type of energy is the spinning plate inside of a microwave oven? MECHANICAL ENERGY

47. QUIZ TIME! Electrical energy is transported to your house through power lines. 3. When you plug an electric fan to a power outlet, electrical energy is transformed into what type of energy? MECHANICAL ENERGY

48. QUIZ TIME! 4. What energy transformation occurs when an electric lamp is turned on? ELECTRICAL ENERGY  ELECTROMAGNETIC ENERGY

49. 5. What types of energy are shown below? Mechanical and Thermal Energy (Don’t forget friction)

50. 6. What type of energy transformation is shown below? Electromagnetic to Chemical Energy