PHYSICS CHAPTER 8
(FORCE X DISTANCE)input =
(FORCE X DISTANCE)output
WHAT OCCURS WHENEVER WORK IS DONE
- APPLICATION OF FORCE - MOVEMENT OF SOMETHING BY THAT FORCE.
ENERGY =
- MOVER OF SUBSTANCES - BOTH A THING AND PROCESS - OBSERVED WHEN IT IS BEING TRANSFERRED OFR BEING TRANSFORMED - A CONSERVED QUALITY - PROPERTY OF A SYSTEM THAT ENABLES IT TO DO WORK - ANYTHING CAN BE TURNED INTO HEAT.
1 JOULE / SECOND
1 WATT
1 KILOWATT
1000 WATTS
SUPPOSE THE PE OF A DRAWN BOW IS 50J AND THE KE IS OF THE SHOT ARROW IS 40J
10J GOES TO WARMING THE BOW.
WHERE IS THE CENTER OF GRAVITY OF A BROOM HELD ABOVE YOUR HEAD.
AT THE BALANCE POINT
SIMILARITIES BETWEEN MOMENTUM AND KINETIC ENERGY
BOTH ARE PROPERTIES OF MOVING THINGS
JAMES WATT
DEVELOPER OF THE STEAM ENGINE
MACHINE
DEVICE FOR MULTIPLYING FORCES OR CHANGING DIRECTION OF FORCES
BY PRODUCT OF NUCLEAR POWER
GEOTHERMAL ENERGY
POTENTIAL ENERGY DUE TO ELEVATED POSITION
GRAVITATIONAL POTENTIAL ENERGY
RAISED RAM OF PILE DRIVER
GRAVITATIONAL POTENTIAL ENERGY
WATER IN AN ELEVATED RESERVOIR
GRAVITATIONAL POTENTIAL ENERGY
WEAKEST OF FOUR KNOWN FUNDAMENTAL FORCES
GRAVITY
A BOY PLAYS SOLITARY SEESAW BY PLACING A LONG PLABK OVER A SMALL ROCK AND SITTING AT ONE END OF THE PLANK. WHEN THE SEESAW IS BALANCED, THE BOYS MASS IS MOST LIKELY
GREATER THAN THE MASS OF THE SEESAW
A PERSON ROTATES ON A STOOL, HOLDING HIS HANDS EMPTY IN HIS LAP. YOU STAND ON A DESK ABOVE HIM AND DROP AND LONG HEAVY BEAN BAG STRAIGHT DOWN SO THAT IT LANDS ACROSS HIS LAP AND IN HIS HANDS. WHAT HAPPENS?
HE SPINS SLOWER - THE BEAN BAG IS NOT ROTATING BEFORE IT CONTACTS THE EXPERIMENTER, SO HE MUST SUPPLY THE ROTATIONAL MOMENTUM REQUIRED TO MAKE IT SPIN AT THE SAME RATE AS HIS LAP, THEREFORE HE ENDS UP SPINNING SLOWER - CONSERVATION OF ROTATIONAL MOMENTUM.
ROTATIONAL INTERTIA ABOUT THE MIDPOINT OF AN OBJECT BECOMES GREATER WITH
INCREASED MASS AND INCREASED DISTANCE TO MASS CONCENTRATION
IS IT EASIER FOR A CIRCUS PERFORMER TO BALANCE A LONG ROD HELD VERTICALLY WITH PEOPLE HANGING OFF THE OTHER END, OR THE SAME LONG ROD WITHOUT THE PEOPLE AT THE OTHER END AND WHY
IT IS EASIER FOR THE PERFORMER TO BALANCE A LONG ROD HELD ABOVE HIM WITH PEOPLE AT THE OTHER END BECAUSE THE ROTATIONAL INERTIA IS GREATER.
IS IT EASIER TO BALANCE A LONG ROD WITH A MASS ATTACHED TO IT WHEN THE MASS IS CLOSER TO YOUR HANG OR WHEN THE MASS IS FURTHER AWAY?
IT IS EASIER WHEN THE MASS IS FARTHER AWAY FROM YOU HAND.
JOE LIVES ON THE EQUATOR AND SALLY LIVES IN ALASKA. WHICH PERSON HAS THE HIGHER ANGULAR VELOCITY DUE TO EARTHS ROTATION?
JOE & SALLY HAVE THE SAME ANGULAR VELOCITY - EVEN THOUGH JOE IS MOVING MORE QUICKLY THAN SALLY, THEY BOTH HAVE THE SAME ANGULAR VELOCITY BECAUSE THEY BOTH COMPLETE ONE REVOLUTION EVERY 24 HOURS.
JOE LIVES ON THE EQUATOR AND SALLY LIVES IN ALASKA. WHICH PERSON HAS THE HIGHER SPEED DUE TO EARTHS ROTATION
JOE BECAUSE THE EQUATOR IS FURTHER FROM THE AXIS OF ROTATION THAN ALASKA.
UNIT OF POWER
JOULE PER SECOND. - WATT
DEPENDS ON THE MASS OF THE OBJECT AND THE SQUARE OF ITS SPEED
KINETIC ENERGY
IF OBJECT SPPED IS DOUBLED
KINETIC ENERGY IS QUADRUPLED
IF YOU PUSHG AGAINST A BRICK WALL FOR SEVERAL MINUTES, YOU DO NO WORK
ON THE WALL - YOU MAY DO WORK ON YOUR MUSCLES, BUT NOT ON THE WALL
PULLEY
OPERATES LIKE A LEVER WITH EQUAL ARMS & CHANGES THE DIRECTION OF THE INPUT FORCE.
INPUT FORCE X INPUT DISTANCE =
OUTPUT FORCE X OUTPUT DISTANCE
EFFICIENCY
PERCENTAGE OF WORK PUT INTO A MACHINE THAT IS CONVERTED INTO USEFUL WORK OUTPUT
BODY IS A MACHINE
SO IT NEEDS ENERGY
MATTER =
SUBSTANCES THAT WE CAN SEE, SMELL, AND FEEL. - OCCUPIES SPACE.
A RING AND DISK INITIALLY AT REST ROLL DOWN A HILL TOGETHER, THE ONE TO REACH THE BOTTOM FIRST IS
THE DISK
WHY IS TWICE AS MUCH WORK IS DONE IN LIFTING A LOAD 2 STORIES INSTEAD OF 1
THE DISTANCE IS TWICE AS GREAT.
KINETIC ENERGY =
THE ENERGY OF MOTION
EQUATION FOR EFFICIENCY =
USEFUL ENERGY OUTPUT/ TOTAL ENERGY INPUT
WORK =
W = FORCE X DISTANCE
GAIN OR REDUCTION OF ENERGY IS THE RESULT OF
WORK - WORK/ENERGY THEOREM
EQUATION FOR WORK
WORK = CHANGE IN KINETIC ENERGY
CONVERSATION OF ENERGY CONCEPT
WORK INPUT = WORK OUTPUT
A GIRL WEIGHS 60LBS AND IS SITTIG ON THE TEETER-TOTTER 3M FROM THE CENTER, HOW FAR FROM THE CENTER SHOULD A 180LB BOY SIT SO THAT THE TEETER TOTTER BALANCES?
1.0METERS - SINCE THE BOY WEIGHS THRE TIMES MORE THAN THE GIRL, HE NEEDS TO BE ONLY 1/3 THE DISTANCE FROM THE CENTER IN ORDER FOR THE TORQUE HE EXERTS ON THE TEETER-TOTTER TO BALANCE THAT OF THE GIRL.
IN AN IDEAL PULLY SYSTEM A WOMEN LIFTS A 100N CRATE BY PULLING A ROPE DOWNWARD WITH A FORCE OF 25N. FOR EVERY 1 METER LENGTH OF ROPE SHE PULLS DOWNWARD THE CRATE RISES
25 CENTIMETERS
A CERTAIN MACHINE IS 30% EFFICIENT. THIS MEANS THE MACHINE WILL CONVERT
30% OF THE ENERGY INPUT TO USEFUL WORK 70% OF THE ENERGY INPUT WILL BE WASTED
DOUBLING SPPED OF AN OBJECT REQUIRES
4 TIMES THE WORK
INCLUDE THE PROPORTIONAL CONSTANT 1/2 AND KINETIC ENERGY =
= 1/2 X MASS X SPEED X SPEED
A CAR TRAVELS IN A CIRCLE WITH CONSTANT SPEED.. THE NET FORCE ON THE CAR IS
DIRECTED TOWARD THE CENTER OF THE CURVE.
APPLYING THE BRAKES TO A SLOW MOVING CAR, HOW IS WORK DONE?
FRICTION FORCE SUPPLIED BY THE BRAKES X DISTANCE
MECHANICAL ENERGY IS RELATED TO
POSITION AND/OR MOTION.
A STRETCHED BOW HAS STORED ENERGY THAT CAN DO WORK ON AN ARROW
POTENTIAL ENERGY
A STRETCHED RUBBER BAND OF A SLINGSHOT HAS STORED ENERGY AND IS CAPABLE OF DOING WORK
POTENTIAL ENERGY
STORED ENERGY HELD IN READINESS
POTENTIAL ENERGY
TWO FORMS OF MECHANICAL ENERGY
POTENTIAL ENERGY KINETIC ENERGY
RECYCLED ENERGY
RE-EMPOYMENT OF ENERGY THAT OTHERWISE WOULD BE WASTED
HOW DOES THE ROTATIONAL INERTIA OF THE ROD WITH THE MASS TOWARD THE BOTTOM COMPARE WITH THE ROTATIONAL INERTIA OF THE MASS TOWARD THE TOP?
THE ROTATIONAL INERTIA OF THE ROD WITH THE MASS CLOSER TO THE TOP IS GREATER THAN THE ROTATIONAL INERTIA OF THE ROD WITH THE MASS CLOSER TO THE BOTTOM.
KINETIC ENERGY DEPENDS ON
THE SQUARE OF VELOCITY
MACHINES ALSO OPERATE AS
A SYSTEM OF PULLEYS (BLOCK & TABLE) - MULTIPLES FORCE.
TWICE THE POWER OF AN ENGINE CAN
DO TWICE THE WORK OF ONE ENGINE IN THE SAME AMOUN OF TIME, OR TWICE THE WORK OF ONE ENGINE IN HALF THE TIME OR AT A RATE AT WHICH ENEGY IS CHANGED FROM ONE FORM TO ANOTHER.
DOOR B IS TWICE AS WIDE AS DOOR A, BUT BOTH DOORS HAVE THE SAME HIEGHT AND THE SAME MASS. A PERSON PUSHES ON THE EDGE OF THE TWO DOORS WITH THE SAME FORCE. WHICH DOOR OPENS MORE QUICKLY?
DOOR A
NEWTONS MOST CELEBRATED SYNTHESIS WAS AND IS OF
EARTHLY AND HEAVENLY LAWS
DRY ROCK GEO THERMAL POWER IS A PRODUCER OF
ELECTRICITY
IS OBSERVED WHEN IT IS BEING TRANSFERRED OR TRANSFORMED
ENERGY
PROPERTY OF A SYSTEM THAT ENABLES IT TO DO WORK
ENERGY
A COMBINATION OF WHAT MAKE UP THE UNIVERSE?
ENERGY AND MATTER
LAW OF CONSERVATION OF ENERGY
ENERGY CANNOT BE CREATED OR DESTROYED IT MAY BE TRANSFORMED FROM ONE FROM INTO ANOTHER BUT THE TOTAL AMOUNT OF ENERGY NEVER CHANGES
GRAVITATIONAL POTENTIAL ENERGY
EQUAL TO THE WORK DONE IN LIFTING IT. - THE FORCE REQUIRED TO MOVE IT UPWARD X THE VERTICAL DISTANCE MOVED AGAINST GRAVITY.
LAW OF UNIVERSAL GRAVITATION
EVERYTHING PULLS ON EVERYTHING ELSE - EVERYBODY ATTRACTS EVERY OTHER BODY WITH A FORCE THAT IS DIRECTLY PROPORTIONAL TO THE SQUARE OF THE DISTANCE SEPARATING THEM
CONSIDER A PROBLEM THAT ASKS FOR THE DISTANCE OF A FAST MOVING CRATE SLIDING ACROSS THE FACTORY FLOOR AND THEN COMING TO A STOP. THE MOST USEFUL EQUATION FOR THIS IS
FD = CHANGE IN 1/2 MV2
EQUATION FOR UNIVERSAL LAW OF GRAVITY
FORCE - M1M2/D2
THE TORQUE EXERTED BY A CROWBAR ON AN OBJECT INCREASED WITH INCREASED
FORCE AND LEVERAGE DISTANCE
SUPPOSE SALLY LIVEDON THE EQUATOR OF A PLANET THAT HAD A RADIUS TWICE THAT OF EARTHS RADIUS AND THAT ROTATED WITH TWICE THE ANGULAR VELOCITY. SALLYS SPEED ON THE PLANET WOULD HOW MUCH FASTER THAN JOE'S SPEED?
FOUR TIMES FASTER THAN
THE TANGENTIAL SPEED ON THE OUTER EDGE OF A ROTATING CAROUSEL IS
FOUR TIMES GREATER THAN TOWARD THE CENTER.
AN OBJECT MOVING WITH TWICE THE VELOCITY OF ANOTHER WITH THE SAME MASS HAS TWICE THE MOMENTUM BUT
FOUR TIMES THE KINETIC ENERGY
ALLOWS SMALL FORCE OVER A LARGE DISTANCE AND LARGE FORCE OVER A SHORT
LEVER
MOST SIMPLE MACHINE
LEVER
ROTATES ON A POINT OF SUPPORT CALLED THE FULCRUM
LEVER
IF THE POLAR ICECAPS MELTED, THE RESULTING WATER WOULD SPREAD OVER THE ENTIRE EARTH. THIS NEW MASS DISTRIBUTION WOULD TEND TO MAKE THE LENGTH OF A DAY
LONGER
CANNOT CREATE ENERGY BUT CAN TRANSFORM ENERGY FROM ONE FORM TO ANOTHER OR TRANSFER ENERGY FROM ONE LOCATION
MACHINE
CANNOT MULTIPLY WORK OR ENERGY
MACHINE
EQUATION FOR POTENTIAL ENERGY
MASS X ACC DUE TO GRAVITY X HEIGHT - MGH
POWER =
MEASURE OF HOW FAST WORK IS DONE P = WORK DONE / TIME INERVAL
ANY MOVING OBJECT HAS BOTH
MOMENTUM AND KINETIC ENERGY
VELOCITY DEPENDENCE
MOMENTUM DEPENDS ON VELOCITY
DIFFERENCE BETWEEN MOMENTUM AND KINETIC ENERGY
MOMENTUM IS A VECTOR QUALITY AND THEREFORE IS DIRECTIONAL AND CAN BE CANCELED. KINETIC ENERGY IS SCALAR QUANTITY AND CAN NEVER BE CANCELED.
EQUATION FOR KINETIC ENERGY
NET FORCE X DISTANCE = KE Fd = 1/2 mv2
UNIT OF WORK
NEWTON-METER (Nm) OR JOULE (J)
CAN A FORCE PRODUCE A TORQUE WHEN THERE IS NO LEVER ARM
NO?
A JOB CAN BE DONE SLOWLY OR QUICKLY. BOTH MAY REQUIRE THE SAME AMOUNT OF WORK, BUT DIFFERENT AMOUNTS OF
POWER
APLLIES TO DECREASING SPEED
REDUCING THE SPPED OF AN OBJECT OR BRING IT TO A HALT
A HUGE ROTATING CLOUD OF PARTICLES IN SPACE GRAVITATE TOGETHER TO FORM AN INCREASINGLY DENSE BALL. AS IT SHRINKS IN SIZE, THE CLOUD
ROTATES FASTER
WHY DOES THE ROTATIONAL INERTIA OF THE ROD WITH THE ATTACHED MASS CLOSER TO YOUR HAND COMPARE THE WAY IT DOES WITH THE ROATIONAL INERTIA OF THE ROD WITH THE ATTACHED MASS FATHER AWAY?
ROTATIONAL INERTIA DEPENDS ON WHETHER THE MASS IS FATHER OR CLOSER TO THE POINT OF ROTATION. THE FARTHER THE MASS IS, THE HIGHER THE ROTATIONAL INERTIA
SOURCES OF ENERGY
SUNLIGHT FUEL CELL CONCENTRATED ENERGY OR NUCLEAR POWER DRY ROCK GEOTHERMAL POWER
WHY IS TWICE AS MUCH WORK IS DONE IN LIFTING TWO LOADS 1 STORY HIGH VERSUS LIFTING 1 LOAD THE SAME VERTICAL DISTANCE
THE FORCE NEEDED TO LIFT TWICE THE LOAD IS TWICE AS MUCH
WHEN DR. HEWITT CUTS THE BROOM RIGHT THROUGH THE CENTER OF GRAVITY, HOW DO THE WEIGHTS OF THE TWO SIDES OF THE BROOM COMPARE?
THE SHORTER SIDE, WHERE THE BRISTLES OF THE BRROM ARE, HAS A GREATER WEIGHT THAN THE HANDS.
HOW DOES THE TORQUE DUE TO THE WEIGHT OF ONE SIDE OF A BRROM EXERTED AROUND THE BALANCE POINT COMPARE WITHT THE TORQUE EXERTED BY THE WEIGHT OF THE OTHER SIDE OF THE BRROM AROUND THE BALANCE POINT.
THE TORQUE DUE TO THE WEIGHT OF THE SHORTER SIDE IS EQUAL IN MAGNITUDE TO THE TORQUE DUE TO THE WEIGHT OF THE LONGER SIDE AND OPPOSITE IN DIRECTION.
KINETIC ENERGY AND WORK OF A MOVING OBJECT =
THE WORK REQUIRED TO BRING IT FROM REST TO THAT SPEED OR THE WORK THE OBJECT CAN DO WHILE BEING BROUGHT TO REST
WHY CANT A FORCE PRODUCE A TORQUE WHEN THERE IS NO LEVER ARM
THERE NEEDS TO BE A LEVER ARM TO PRODUCE ARM TO PRODUCE TORQUE.
YOU DO WORK WHEN PUSHING A CART WITH A CONSTANT FORCE. IF YOU PUSH THE CART TWICE AS FAR, THEN THE WORK YOU DO IS
TWICE AS MUCH
WORK IS DONE IN LIFTING A BARBELL. HOW MUCH WORK IS DONE IN LIFTING A BARBELL THAT IS TWICE AS HEAVY AS THE SAME DISTANCE
TWICE AS MUCH - TWICE THE FORCE FOR THE SAME DISTANCE MEANS TWICE THE WORK DONE ON THE BARBELL
THE WORK DONE IN BRINGING A MOVING CAR TO A STOP IS THE FORCE OF TIRE FRCTION X STOPPING DISTANCE. IF THE INITIAL SPEED OF THE CAR IS DOUBLED, THE STOPPING DISTANCE IS
TWICE THE SPEED MEANS FOUR TIMES THE KINETIC ENERGY AND FOUR TIMES THE STOPPING DISTANCE.
DOES A CAR HOISTED FOR REPAIRS IN A SERVICE STATION HAVE INCREASED POTENTIAL ENERGY RELATIVE TO THE FLOOR?
YES BECAUSE IF THE CAR WERE TWICE AS HEAVY, ITS INCREASE IN PE WOULD BE TWICE AS GREAT
MUST A CAR WITH MOMENTUM HAVE KINETIC ENERGY
YES DUE TO MOTION ALONE.
