ALL RIGHT, SALEETA
AND TONY...
TO HAWK?
DO YOU EV STOP MOVING?
( sighs )
 Captioning sponsored by THE
 U.S. DEPARTMENT OF EDUCATION
 SPORTS FIGURES
PUT YOUR BRAIN IN THE GAME.
Man's voice:
HERE'S YOUR PIZZA.
WHAT HAPPENS WHEI DROP THIS
BOWLING BALL DOWN THE HALF-PIPE?
OKAY, I GUESS WE'D EXPECT THAT.
THE BOWLING LL GOES
A LITTLE LESS HIGH EACH TIME
AND EVENTUALLY,
HE'S GOING TO STOP.
WHAT HAPPENS N
WE DROP HIM DOWN
THE HALF-PIPE?
HE JUST KEEPS GOING
AND GOING ANGOING.
WHY IS THAT?
HE SHOULD GRADUALLY COME
TO A STOP
JUST LIKE
THE BOWLING BALL.
FOR YEARS, PEOPLE BELIEVED
THAT THEY COULD CREATE
A PERPETUAL MOTI MACHINE.
A PERPETUAL MOTION MHINE
WOULD HAVE
THE PERFECT BALANCE OF ENERGIES.
ONCE IT STARTED,
IT WOU NEVER STOP.
IT WOULD RUN FOREVER,
WITH NO COAL, NO GAS
NO ELECTRICITY,
NO NOTHING!
BUT THEY WERE WRONG.
EY'RE COMPLETELY WRONG.
JUST ALL COMPLETELY WRONG.
THERE'S JUST NO WAY IT COULD BE!
RIGHT?
( cheering )
BUT HAS TONY FIGURED IT OUT?
( whistle blows )
Man's voice:
OKAY...
( laughing  )
WE SPEEDING?
WHAT'S THE DIFFERENCE BETWEEN
A BOWLING BALL AND TONY HAWK?
THE BOWLING BALL OBEYS
THE LAW OF CONSERVATION
OF ENERGY.
 THE BOWLING BALL, THE HALF-PIPE
AND THE AIR INSIDE THE HALF-PIPE
 MAKE AN ENERGY SYSTEM.
CONSERVATION OENERGY MEANS
THAT ENERGY WITHIN THE SYSTEM
MUST BE CONSERVED.
IT CAN'T GAIN ENERGY OR LO IT.
THE TOTAL AMOUNT OF ENERGY
WITHIN THE SYSTEM
REMAINS THE SAME.
WEIRD, RIGHT?
OBVIOUSLY,
THE BOWLING BALL HAS ERGY.
IT'S MOVING, RIGHT?
IFT HIT ME,
I'D FEEL ITS ENERGY.
IT'D DO WORK.
IT'D BREAK MY ANKLE.
BUT IF ENERGY CAN BE
NEITHER CREATED NOR DESTROYED
WHY DOES IT EVENTUALLY
COME TO A STOP
WAS ITS ENERGY DESTROYED?
BRUNSY!
WHAT HAPPENED TO YOUR ENERGY?
THIS GUY HAS PLENTY OF ENERGY.
HE'S TONY HAWK.
HE'S DONE EVERYTHING
THERE IS TO DO
 THE WORLD OF SKATEBOARDING,
AND HE H HIS OWN VIDEO GAME
SO HE'S IN PERPETUA MOTION.
( cheering )
SO, TONY, WHAT IF YOU
PUSH OFF AND COAST?
WHATAPPENED?
WELL, THE FRICTION
BETWEEN MY WHEELS
AND THE GROUND STOPS ME
AND THERE WAS AL FRICTION
WITH THE AIR.
SO, THEN, WAS YOUR
ENERGY DESTROYED?
WELL, YOJUST SAID
THAT CAN'T BE.
BUT... WHERE DID IT GO?
IT WAS TRANSFERRED.
TONY HAD MOVING ENERGY
WHICH IS CALLED
"KINETIC ENEY."
THE KINETIC ENERGY
WAS CONVERTED
TO HEAT ENERGY
BY THE FRICTION
BETWEEN E WHEELS
AND THE GROUND.
FRICTION CREATES HEAT, RIGHT?
YOU RUB TWO OBJECTTOGETHER,
AND YOU GET HEAT.
AND HEAT IS A FORMF ENERGY.
SO THE BALL'S KINETIC ENERGY
GRADUALLY GETS CONVERTED
TO HEAT ENERGY.
OH!
SEE?
THSURFACE OF THE BALL
AND THE HALF-PIP
AND THE AIR THAT IT ENCOUNTERED
ARE ALL
JUST A LITTLE BIT HOTTER.
THE ENERGY STAYED THE SAME.
IT JUST CHANGED FORMS.
SO, ENERGY WAS CONSERVED.
BRUNSWICK, YOU'RRUNNING
A LITTLE TEMPERATURE.
SEE, A HALF-PIPE IS
AN ENERGY CONVERSION DEVICE.
HE HAS KINETIC ENERGY--
"KE"-- BECAUSE HE'S MOVING.
NOW, SOME OF THAT ENERGY
GETS CONVERTED TO HEAT ENERGY
BUT AS HE GOES UP THE SIDES
MOST OF HIS KINETIC ENERGY
IS BEING CONVERTED
TO GRAVITATIONAL POTENTIAL
ENERGY, "GPE."
IF YOU PUSH OFF AND
COAST, YOU STOP.
SO, HOW DO
YOU ADD ENERGY
INTO THE SYSTEM SO
YOU CAN KEEP GOING?
YOU PUSH OFF
WITH YOUR FOOT.
TO GAIN ENERGY IN A SYSTEM,
YOHAVE TO DO WORK.
( cheering )
( instinct voices )
IN THE HALF-PIPE,
HE'S NOT PUSHING OFF AT ALL.
BUT HE GOES HIGHER AND HIGHER
EACH PASS
SO HE MUST BE ADDINGNERGY
TO THE SYSTEM.
  TONY COMES DOWN THE WALL,
 HE DROPS INTO A CROUCH.
 THEN, AS HE ARTS TO GO UP
 THE OTHER SIDE
 HE EXTENDS HIS LEGS.
WELL, TO KEEP YOUR SPEED UP
AND TO GET HEIGHT OFF THE LIP
YOU HAVE TO PUMP.
SO, THAT'S WHAT
YOU'RE DOING
WHEN YOU CROUCH DOWN?
RIGHT. AS YODROP DOWN,
YOU GO DOWN INTO A CROUCH
AND AS YOU GO
THROUGH THE TRANSITION
YOU EXTEND YOUR LEGS.
AND IT WOULD ONLY TAKE ME
A LITTLE WHILE
TO START FROM DOWN HERE
AND GET TO THE TOP.
AND THAT'S HOW YOU DO IT.
( laughs )
SO, YOU'RE RAISING
AND LOWERING YOURSF.
BUT HOW DOES THAT
GIVE YOU MORE ENERGY?
IT'S JUST LIKE
PUMPING  A SWING.
HE'S RIGHT-- YOU BEND YOUR LEGS
AT THE BOTTOM OF THE ARC
AND YOU EXTEND AS YOU GO UP.
BUT WHY?
IF I SHORTEN
ON THE UPSWING
AND LETHEN
ON THE DOWNSWING...
IT STARTS GETTING HIGHER.
YEAH, WHAT DOES
THAT TELL US?
IT GAINS ENERGY?
IT'S KIND OF LIKE TONY--
LIFTING ON THE UPART
AND DROPPING
ON THE DOWN PART.
BUT LIFTING
AND DROPPING WHAT?
WEIGHT.
OKAY. , SOMEHOW LIFTING
AND DROPPING WEIGH
GIVES US ENERGY.
HOW DOES THAT WORK?
IF IROP THE BOWLING BALL
FROM HERE
IT HAS ENERGY-- IT'S MOVG.
ANY OBJECT THAT'S MOVING
HAS KINETIC ENERGY.
AND WE KNOW THAT IT HAS ENERGY
BECAUSE IT DOES WORK.
SEE? IT MADE THIS DENT
HERE IN THE GROUND.
THAT'S THE DEFINITION OF ENERGY.
AN OBJECT HAS ENERGY
IF IT DOES WORK.
AND WORK IS A FORCE TIMES...
A DISTANCE.
THE HIGHER YOU LIFT A WEIGHT
THE MORE POTENTIAL ENERGY IT HAS
AND THE MORE KINETIC ENERGY
IT WILL HAVE
WHEN YOU DROP IT.
THATAKES SENSE, RIGHT?
THE FASTER SOMETHING GOES,
THE MORE KINETIC ENERGY IT HAS!
( sputtering )
OH, LOOK, IT DID WAY MORE WORK.
IT DUG TS REALLY DEEP HOLE.
THAT PROVES IT HAD MORE ENERGY.
EVERY OBJECT HAS
A CENTER OF GRAVITY
OR A CENTER OF MASS.
IT'S THE AVERAGE
POSITION OF MASS
OR WHERE THE MASS
IS CONCENTRAD.
AND FOR MOST PEOPLE,
IT'S RIGHT ABOUT HERE.
NOW, IF I ING BACK AND FORTH,
JUST LIKE THIS,  PUMPING
MY CENTER OF MASS
DESCRIBES AN ARC
BUT IF I DO THIS...
SEE? PUMPING IS RAISING
AND LOWERING MY CENTER OF MASS
BY CHANGING MY SHAPE.
BECAUSE I RAISE
MY CENTER OF MASS
I HAVE GREATER POTENTIAL ENERGY
UP HIGH
WHICH GIVES ME GREATER
KINETIC ENERGY WHEN I FALL.
 IF TONY STAYED IN A CROUCH
 ALL THE WAY
 THROUGH THE HALF-PIPE
 HIS CENTER OF MASS
 WOULD ONLY RISE TO HERE.
 BUT IF HE COS OUT
 OF HIS CROUCH, EXTENDS HIS LEGS
 HE LIFTS
 HIS CENTER OF MASS HIGHER
 AND GAINS
 MORE POTENTIAL ENERGY.
 THEN, E FURTHER
 SOMETHING FALLS
 THE MORE KINETIC ENERGY IT HAS,
 RIGHT?
 WELL, LOOK, ON THE WAY DOWN
 TONY DROPS INTO A CROUCH.
 HE LETS HIS CENTER
 OF MASS DROP FURTHER.
  FALLS LONGER THAN IF
 HE WERE STANDING UPRIGHT.
AND BEFORE TOO LONG,
NY HAS ENOUGH ENERGY
TO BRING HIM ALL THE WAY UP HERE
ABOVE THE RIM, LIKE THIS
TO DO ALL THESE
REALLY COOL AERIALS.
GREATEPOTENTIAL ENERGY
UP HERE...
AND GREATER KINETIC ENER
DOWN HERE.
GOING INTO A TUCK LIKE THIS
ALLOWS TONY TO DROP
HIS CENTER OF MASS EVEN LOWER.
YOU CAN'T CHANGE YR SHAPE...
OR RAISE YOUR CENTER OF MASS
HIGHER, OR DROP IT LOWER.
I'M SORRY, BRUNSWI, BUT...
YOU'RE JUST A BOWLING BALL.
IT'S THE SAME WITH T YO-YO.
SHORTENING THE STRING,
YOU LIFT THE WEIGHT HIGHER.
AND LENGTHENING
THE STRING
YOU DROP THE
WEIGHT LOWER
YOU GAIN ENERGY.
BUT WAIT A SECOND.
WE SAID BEFORE
THAT YOU COULD NTHER
CREATE ENERGY,
NOR DESTROY IT.
WE'RE GAINING ENERGY.
ARE WE CREATING IT?
, GOOD QUESTION.
 IS TONY VIOLATING THE LAW
 OF CONSERVATION OF ENERGY?
NO, BECAUSE HE'S PUTTING WORK
INTO THE SYSTEM.
LIKE WHEN I PULL ON THIS STRING
TO RAISE THE YO-YO
AND IT SWINGS-- I'M DOING WORK.
AND WORK PUTS ENERGY
INTO THE SYSTE
JUST LIKE THIS MACHINE.
 COAL GIVES UP
 ITS POTENTIAL ENERGY
TO PUT WORK INTO THE SYSTEM,
TO GIVE IT THE ENERGY
TO OVERCOME FRICTION
AND INERTIA.
GHT, GREG?
RIGHT.
IT TOOK WORK TO RAISE
THE BOWLING BALL TO HERE.
 DAVID'S GYPSY DRIFTER
 HAD TO DO EVEN MORE WORK
 TO RAISE THE BOWLING BALL
 UP TO HERE.
THE AMOUNT OF WORKOU DO HAS
TO EQUAL THE AMOUNT OF ENEY
YOU PUT INTO THE SYSM.
AND IT ALL HAS TO BE CONSERVED.
CHECK THIS OUT
WHEN TONY STRAIGHTS HIS LEGS,
HE'S DOING WORK--
LIING HIS CENTER OF MASS
IS WORK.
HE'S CONVERTING THE CHEMICAL
POTENTIAL ENERGY IN HIS BODY
TO MECHANICAL ENERGY
IN HIS MUSCLES TO DO THE WORK
 TO GIVE HIM THE ENERGY
 AND GET HIM UP THE HALF-PIPE.
 THAT ENERGY IS WHAT LIFTS HIM
 INTO THE AIR.
WELL, TONY, JUST
STRAIGHTENING YOUR LEGS
DOESN'T SEEM LIKE WORK.
WELL, I'M NOT JUST
STRAIGHTENING THEM--
I'M LIFTING MY BODY'S WEIGHT.
SO, JUST SQUAT AND LIFT
A FEW TIMES
AND YOU'LL SEE THAT IT'S WORK--
FORCE OVER A DISTANCE.
OH, AND HERE'S A
REALLY COOL THING.
WE CAN FIND THE NUMBER
AT SHOWS EXACTLY
HOW MUCH ENERGY
YOUR WORK IS ADDING TO
THE SYSTEM BY PUMPING.
HOW DO YOU MEASURE ENERGY?
WE MEASURE IT IN JOULE
HOW MUCH IS A JOULE?
A JOULE IS T FORCE
OF ONE NEWTON
EXERTED OVER THE DISTANCE
OF ONE METER.
THIS ONGE WEIGHS
ABOUT ONE NEWTON--
THAT'S THE METRIC EQUIVALENT
OF WEIGHT.
AND IF I LIFT THIS ORANGE
OVER MY HEAD
THAT'S ABOUT A METER.
SO, LIFTING THIS ORANGE TAKES
ABOUT ONE JOULE OF ENERGY.
NOW, IF I EAT THIS ORANGE,
THAT'S GOING TO GIVE ME
420,000 JOULES OF ENERGY
FROM THE CALORIES.
SO, EATING AN ORANGE ALLOWS ME
TO LIFT AN ORANGE
ABOUT 420,000 TIMES.
LET'S SEE. ONE...
TWO... THREE...
( crowd cheering )
TONY, HOW DO YOU
START IN A HALF-PIPE?
WELL, I STAND ON THE TOP,
D THEN I JUST DROP.
 OKAY, LET'S FIGURE OUT
 YOUR GRAVITATIONAL
 POTENTIAL ENERGY.
NO, IT'S A REALLY
SIMPLE EQUATION.
IT LOOKS LIKE THIS.
GPE EQUALS WEIGHT
TIMES HEIGHT.
SO, HOW MUCH DO YOU WEIGH?
ABOUT 150 POUNDS.
OKAY, THAT'S ABOUT...
700 NEONS...
WELL, WAIT, WHAT'S A NEWTON?
I JUST EXPLAINED THAT.
WELL, I WASN'T THERE.
WELL, A-NEWTON
IS THE METRIC
EQUIVALENT OF WEIGHT.
I THOUT THAT WAS GRAMS,
LIKE KILOGRAMS.
GRAMS MEASURE MASS
WHICH IS DIFFERENT
FROM WEIGHT.
WEIGHT IS THE FORCE
THAT GRAVITY'S
PULLING YOU DOWN WITH.
LI POUNDS
AND CUSTOMARY UNITS.
MASS IS THE
MEASURE OF INERTIA.
OKAY, LES GET
BACK TO OUR EQUATION.
OKAY, SORRY.
SO, I WEIGH 700 NEWTONS.
YEAH. NOW, HOW
HIGH ARE WE HERE?
OUT 15 FEET.
 TONY'S CENTER
 OF MASS IS HERE
 ABOUT THREE FEET HIGHER
 THAN THE RIM, SO 18 FEET.
 LET'S CALL THAT 5½ METERS.
 TO FIND HIS GPE, WE JUST
 MULTIPLY TONY'S WEIGHT--
 700 NEWTONS--
 BY HIS HEIGHT-- 5½ METERS
 TO GET 3,850 JOULES
 OF POTENTIAL ENERGY.
WOW, LET'SURN THAT
INTO KINETIC ENERGY.
OKAY.
GO FOR IT.
 THAT MEANS THAT DOWN HERE,
 TONY WILL HAVE A LTLE LESS
 THAN 3,850 JOULES
 OF KINETIC ENERGY
 BECAUSE OF WHAT'S LOST
 TO FRICTION.
NOW, TONY'S CENTER OF MASS
IS WAY UP HERE.
HE'S EVEN LIFTED HIS LEGS
TO GET AS MUCH OF HIS WEIGHT
AS HIGH AS POSSIBLE.
JUST LIKE ON THE SWING.
NOW, BECAUSE HE'S HIGHER,
HE HAS A NEW GPE.
BUT WE CAN FIGURE THAT OUT.
 TONY'S CENTER OF MASS
 IS NOW ABOUT 6½ METERS
 FROM THE BOTTOM
 OF THE HALF-PIPE.
 HIS WEIGHT HASN'T CHANGED--
 700 NEWTONS--
 SO, 700 TIMES ½ IS 4,550
 JOULES OF POTENTIAL ENERGY.
 HIS ENERGY IS GREATER.
WE KNOW THAT TONY ADDED
AT LEAST 700 JOULES OF ENERGY
TO THE SYSTEM.
OH, ACTUALLY,
THAT MAKES SENSE
BECAUSE LIFTING MY CENTER
OF MASS OUT OF A CROUCH
IS LIFTING 700 NEWTONS
ABOUT A METER
AND THAT WOULD BE
700 JOULES.
RIGHT.
WELL, THAT'S COOL.
PHICS IS
TOTALLY COOL.
SO...
A BOARDER IN THE HALF-PIPE
 ISN'T A PERPETUAL
 MOTION MACHINE.
HE IS OBEYING THE LA
OF CONSERVATION OF ENERGY.
OH, OH, EVERYTHING'S
OKAY HERE, OFFIC.
OKAY, GUYS, WHAT DID WE LEARN?
THAT IN A SYSTEM,
ENERGY MUST BE CONSERVED.
THAT'S THE LAW OF CONSERVATION
OF ENERGY.
ENERGY CAN'T BE CREATED
OR DESTROYED
BUIT CAN BE CONVERTED
OR TRANSFERRED TO OTHER FORMS.
BUT NO PRACTICAL,
REAL SYSTECAN GO ON FOREVER
WITHOUT ADDING ENERGY.
AND WHEN YOU ADD ENERGY,
YOU  WORK.
FOR TONY IN THE HALF-PIPE
TYPES OF ENERGY ARE
GRAVITATIONAL POTENTIAL ENERGY
KINETIC ENERGY AND HEAT ENERGY.
AND WORK AND ENERGY
ARE MEASURED IN JOULES.
OKAY. GOOD... WORK.
HEY, WE SAID ENERGY
CAN NEITHER BE CREATED
NOR DESTROYED, RIGHT?
SO, WHERE DO WE GET
THE ENERGY
TO DO THE WORK
TO LIFT YOUR WEIGHT?
YOUR MUSCLES USE
CALORIES TO DO THAT.
CALORIES ARE LIKE JOULES--
A UNIT OF ENERGY
YOU GET FROM FOOD.
SO, WE COU EVEN FIGURE OUT
HOW MANY CALORIES OF ENERGY
YOU USE
TO LIFT YOUR WEIGHT
EACH TIME.
THAT'D BE COOL.
HMM.
YOU CAN LEARN HOW TO DO IT
FROM OUR WEB SITE
AT SPORTSFIGURES.ESPN.COM.
WELL, THAT'S IT.
WE'D LIKE TO THANK
 NY HAWK...
2001 NEXT CUP CHAMPION,
ALAN YOUNG...
AND OUR STUDENTS
FROM CARLSBAD HIGH:
 DUSTY
 ANDY
 LILA
 AND EMILY
FOR HELPING US OUT HERE TODAY
ON ESPN SPORTS FIGURE
"PERPETUAL MOTION."
ANNOUNCER:
 LET'S GO BACK IN TIME
 FOR A SPORTS FIGURES CLASSIC.
