1. WORK

2. THE USE OF FORCE TO MOVE AN OBJECT SOME DISTANCE
DEFINITION OF WORK
THE USE OF FORCE TO MOVE AN OBJECT SOME DISTANCE

3. WORK IS DONE ONLY WHEN:
THERE HAS BEEN MOVEMENT OVER SOME DISTANCE AND
THE DISTANCE THE OBJECT MOVED WAS IN THE SAME DIRECTION AS THE FORCE APPLIED.

4. FORCE (N) X DISTANCE (m)
FORMULA FOR WORK
WORK =
FORCE (N) X DISTANCE (m)

5. UNITS FOR WORK
NEWTON-METER = JOULE
A FORCE OF 1 NEWTON EXERTED ON AN OBJECT THAT MOVES 1 METER DOES 1 NEWTON-METER OR (1 JOULE) OF WORK.

6. SAMPLE WORK PROBLEM W= F X D W = 900 N X 100 m
A MOUNTAIN CLIMBER EXERTS A FORCE OF 900-N TO SCALE A 100-m CLIFF. HOW MUCH WORK IS DONE BY THE MOUNTAIN CLIMBER?
W= F X D
W = 900 N X 100 m
90,000 n-m OR JOULES OF WORK

7. W = F x D FORCE (20N) X DISTANCE (30m)
WORK PROBLEMS
JANICE PULLS A WAGON FOR 30 METERS. IF SHE USES A FORCE OF 20N TO PULL, HOW MUCH WORK DOES SHE DO?
W = F x D FORCE (20N) X DISTANCE (30m)
20N X 30m = 600J

8. HOW MUCH WORK IS DONE IN LIFTING A 12N HAMMER FROM THE FLOOR TO A HEIGHT OF 2m?
W = 12N X 2m
= 24J of work is done

9. ENERGY

10. THE ABILITY TO DO WORK OR CAUSE A CHANGE
ENERGY
THE ABILITY TO DO WORK OR CAUSE A CHANGE

11. ENERGY & WORK
IF WORK IS THE USE OF FORCE TO MOVE AN OBJECT SOME DISTANCE, THEN WORK IS ALSO THE TRANSFER OF ENERGY

12. IF AN OBJECT DOES WORK, IT USES ENERGY.
SO…
BECAUSE WORK & ENERGY ARE DIRECTLY RELATED, BOTH ARE MEASURED IN JOULES

13. KINETIC ENERGY
POTENTIAL ENERGY
THE ENERGY OF MOTION
STORED ENERGY

14. GRAVITATIONAL POTENTIAL ENERGY
POTENTIAL ENERGY THAT’S DEPENDENT ON HEIGHT

15. GRAVITATIONAL POTENTIAL ENERGY (G. P. E
GRAVITATIONAL POTENTIAL ENERGY (G.P.E.) = m•g•h MASS X ACCELERATION DUE TO GRAVITY (9.8m/s2) X HEIGHT ABOVE THE GROUND

16. G.P.E. CALCULATION G.P.E. = m•g•h 5kg X 9.8m/s2 X 1.5m
A BOX WITH A MASS OF 5kg IS SITTING ON A CABINET THAT IS 1.5m high. What is the G.P.E.?
G.P.E. = m•g•h
5kg X 9.8m/s2 X 1.5m
73.5N·m or 73.5J

17. ELASTIC POTENTIAL ENERGY
THE ENERGY ASSOCIATED WITH OBJECTS THAT CAN BE STRETCHED OR COMPRESSED

18. POTENTIAL ENERGY

19. KINETIC ENERGY =
MASS X VELOCITY2 2
OR…
½ MV2

20. IF YOU INCREASE MASS OR VELOCITY, YOU INCREASE KINETIC ENERGY

21. KINETIC ENERGY PROBLEM
A 50kg ROCK IS TRAVELING 5 METERS PER SECOND. WHAT IS THE KINETIC ENERGY OF THE OBJECT?
K.E. = ½ MV2
½ X 50kg X (5m/s)2 =
25kg X 25m2/s2 =
625J

22. MECHANICAL ENERGY
THE ENERGY POSESSED BY AN OBJECT DUE TO ITS MOTION OR POSITION
OR…
AN OBJECT’S COMBINED POTENTIAL AND KINETIC ENERGY

23. MECHANICAL ENERGY THE ENERGY ASSOCIATED WITH MOTION
SUM OF KINETIC AND POTENTIAL ENERGY
EXAMPLES: WATER, WIND, MOVING VEHICLE, WALKING, HITTING A BALL, SOUND, BLOOD FLOW.

24. MECHANICAL ENERGY = POTENTIAL ENERGY + KINETIC ENERGY
OR…
ME = PE + KE

25. THE LAW OF CONSERVATION OF ENERGY
ENERGY CAN BE NEITHER CREATED NOR DESTROYED, IT CAN ONLY BE CHANGED FROM ONE FORM TO ANOTHER

26. MANY TIMES A SERIES OF ENERGY CONVERSIONS TAKE PLACE IN DOING A SPECIFIC JOB.
TURN TO PAGE 127 AND DESCRIBE THE ENERGY CONVERSIONS TAKING PLACE IN THE PICTURE

27. CHANGES IN THE FORMS OF ENERGY
ENERGY CONVERSION
CHANGES IN THE FORMS OF ENERGY
ONE OF THE MOST COMMON IS CHANGING FROM: KINETIC TO POTENTIAL OR POTENTIAL TO KINETIC

30. Potential Energy and Conservation of Energy

31. Kinetic vs. Potential
Image source:

32. ALL FORMS OF ENERGY CAN BE CONVERTED TO OTHER FORMS:
OTHER CONVERSIONS
ALL FORMS OF ENERGY CAN BE CONVERTED TO OTHER FORMS:
EXAMPLES:

33. LOSING ENERGY
IN MOST ENERGY TRANSFORMATIONS, SOME OF THE ENERGY IS TRANSFORMED INTO HEAT DUE TO FRICTION (INCLUDING AIR RESISTANCE)

34. G.P.E. = MGH ENERGY THE ENERGY OF MOTION
STORED ENERGY: THE ENERGY OF SHAPE OR POSITION
THE ENERGY OF MOTION
IF YOU INCREASE MASS OR VELOCITY, YOU INCREASE KINETIC ENERGY
ELASTIC = ENERGY ASSOCIATED W/OBJECTS THAT CAN BE STRETCHED OR COMPRESSED
GRAVITATIONAL = ENERGY THAT’S DEPENDENT ON HEIGHT
ENERGY
KINETIC = ROCK ROLLING DOWN A HILL
POTENTIAL = ROCK SITTING ON TOP OF THE HILL
K.E. = ½ MV2
G.P.E. = MGH

35. OTHER FORMS OF ENERGY
THERMAL
CHEMICAL
NUCLEAR
ELECTROMAGNETIC

36. THERMAL ENERGY
THE ENERGY AN OBJECT HAS DUE TO THE MOTION OF ITS MOLECULES
THE FASTER ATOMS MOVE THE MORE THERMAL ENERGY THE OBJECT HAS
OFTEN RESULTS FROM FRICTION
EXAMPLES: ANY CHANGE IN TEMPERATURE OR PHASE OF MATTER (I.E. WATER BOILING)

37. CHEMICAL ENERGY
THE ENERGY STORED IN CHEMICAL BONDS THAT HOLD CHEMICAL COMPOUNDS TOGETHER
USUALLY, WHEN BONDS ARE BROKEN, THEN ENERGY IS RELEASED OR ABSORBED
EXAMPLES: BURNING FUEL (COAL OR WOOD), FOOD, FIREWORKS.

38. NUCLEAR ENERGY POTENTIAL ENERGY STORED IN THE NUCLEUS OF AN ATOM.
HEAT & LIGHT ENERGY ARE RELEASED WHEN NUCLEI FUSE (FUSION) OR WHEN THE NUCLEUS OF AN ATOM SPLITS (FISSION).
EX: SUN (FUSION), NUCLEAR POWER (FISSION)

39. ELECTROMAGNETIC ENERGY
THE ENERGY ASSOCIATED WITH ELECTRICAL AND MAGNETIC INTERACTIONS
ELECTRICAL ENERGY: POWER LINES w/ELECTRICTY, HOME WIRING.
RADIANT ENERGY: ENERGY CARRIED BY LIGHT, INFRARED WAVES, X-RAYS.

40. MORE ENERGY CONVERSIONS
IT IS POSSIBLE TO TRANSFER, OR CONVERT ONE FORM OF ENERGY TO OTHER FORMS:
EXAMPLES: RUBBING HANDS TOGETHER

41. POWER

42. THE RATE AT WHICH YOU DO WORK
DEFINITION OF POWER
THE RATE AT WHICH YOU DO WORK

43. FORCE X DISTANCE TIMEXX
FORMULA FOR POWER
WORK
TIME
FORCE X DISTANCE TIMEXX

44. WATT 1 WATT IS EQUAL TO 1 JOULE PER SECOND
SI UNIT OF POWER
WATT 1 WATT IS EQUAL TO 1 JOULE PER SECOND
1 w = 1 J/s

45. SAMPLE POWER PROBLEMS
A SMALL MOTOR DOES 4000 J OF WORK IN 20 SECONDS. WHAT’S THE POWER OF THE MOTOR IN WATTS?
P = W/t or F•d/t
4000J / 20s
= 200w OF POWER

46. POWER PROBLEMS
AN ELECTRICAL CHARGER USES 144J IN 30S TO CHARGE A MOBILE PHONE. HOW MUCH POWER DID THE CHARGER USE?
P = W/t
144J / 30s
4.8 w OF POWER

47. AN AIRPORT CONVEYOR BELT DOES 1200J OF WORK TO MOVE A SUITCASE IN 20S
AN AIRPORT CONVEYOR BELT DOES 1200J OF WORK TO MOVE A SUITCASE IN 20S. WHAT’S THE POWER OF THE CONVEYOR BELT?
P = W / t
1200J / 20s
60 w OF POWER

48. P = FORCE X DISTANCE / TIME
A MACHINE MOVES AN OBJECT WITH A FORCE OF 50N A DISTANCE OF 28 M IN 70 S. HOW MUCH POWER DID IT TAKE?
P = FORCE X DISTANCE / TIME
50N X 28m = 1400N-m / 70s
= 20w OF POWER USED

49. CALCULATING POWER FROM ENERGY
YOU CAN MEASURE ENERGY USED BY DIVIDING THE ENERGY BY TIME
POWER =
ENERGY TIME

50. SAMPLE POWER PROBLEMS
A LIGHT BULB USED 600 J OF ENERGY IN 6 SECONDS, WHAT IS THE POWER OF THE LIGHT BULB?
P = E/t
600J / 6s
= 100 J/s OR WATTS OF POWER

51. INCREASING SPEED REQUIRES MORE ENERGY
HOW ENERGY RELATES TO:
SPEED
INCREASING SPEED REQUIRES MORE ENERGY

52. AN OBJECT THAT HAS MOMENTUM HAS KINETIC ENERGY
HOW ENERGY RELATES TO:
MOMENTUM
AN OBJECT THAT HAS MOMENTUM HAS KINETIC ENERGY

53. FORCE HOW ENERGY RELATES TO:
A FORCE IS REQUIRED TO CHANGE THE MOTION OF AN OBJECT. THIS IS WORK, & IF IT’S DOING WORK IT CHANGES THE ENERGY OF THE OBJECT

54. POWER HOW ENERGY RELATES TO:
SINCE POWER IS THE RATE AT WHICH WORK IS DONE, IT MUST ALSO BE THE RATE AT WHICH ENERGY IS CONSUMED BECAUSE IT TAKES ENERGY TO DO WORK.

55. WORK HOW ENERGY RELATES TO:
WORK DONE ON A MACHINE MEANS THAT ENERGY GOES INTO THE MACHINE. BECAUSE ENERGY IS CONSERVED, WORK IS CONSERVED. FRICTION ENERGY IS NOT LOST BUT CONVERTED TO HEAT ENERGY.