WORK

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

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.

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

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.

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

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

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

ENERGY

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

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

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

KINETIC ENERGY POTENTIAL ENERGY THE ENERGY OF MOTION STORED ENERGY

GRAVITATIONAL POTENTIAL ENERGY POTENTIAL ENERGY THAT’S DEPENDENT ON HEIGHT

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

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

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

POTENTIAL ENERGY

KINETIC ENERGY = MASS X VELOCITY2 2 OR… ½ MV2

IF YOU INCREASE MASS OR VELOCITY, YOU INCREASE KINETIC ENERGY

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

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

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.

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

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

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

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

Potential Energy and Conservation of Energy

Kinetic vs. Potential Image source: http://www.glenbrook.k12.il.us/gbssci/phys/mmedia/energy/ce.html

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

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

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

OTHER FORMS OF ENERGY THERMAL CHEMICAL NUCLEAR ELECTROMAGNETIC

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)

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.

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)

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.

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

POWER

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

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

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

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

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

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

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

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

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

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

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

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

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.

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.