WHOA!
■■
 SPORTS FIGURES.
PUT YOUR BRAIN IN THE GAME.
THAT'S NUTS!
LUGERS ARE INTO SPEED.
THE WHOLE DEAL IS TO GO FASTER
AND FASTER, RIGHT?
WHOO!
OOH!
OF COURSE,
CONTROL'S PART OF IT, TOO.
BUT LET'S SAY
WE JUST WANTED TO GO FAST
REALLY FAST...
IF THE HILL IS LONG ENOUGH
YOU COULD GO AS FAST
AS YOU WANTED.
MAYBE EV BREAK
THE SOUND BARRIER.
UH-OH.
THERE ARE LAWS
ABOUT THE SPEED LIMIT
FOR A STREET LUGE.
BUT THEY'RE NOT WRITTEN
IN ANY TRAFFIC CODES
OR POSTED ON ANY SIGNS.
SEE, IN PHYSICS,
THERE ARE LAWS
ABOUT THE TOP SPEED
ANY OBJECT CAN GO.
WE'RE TALKING
ERMINAL VELOCITY."
( groaning )
SURE, IF YOU GO TOO FAST
IN A TURN
THAT'S A KIND OF...
TERMINAL VELOCITY.
BUT THE TERMINAL VELOCITY
WE'RE TALKING ABOUT
IS THE TOP SPEED
A FALLING OBJECT CAN GO.
( grunts )
AND A LUGE...
( grunting )
...IS A FALLING OBJECT.
( gasps )
TO HELP US TAKE A LOOK,
WE'VE GOT DARREN LOTT.
HE'S BEEN STREET LUGING
SINCE THE LATE '70s.
 HE'S ALSO AN X GAMES MEDALIST
 AND HE'S WON RACES WORLDWIDE.
 HE ALSO HOLDS THE GUINNESS BOOK
OF WORLD RECORDS RECORD
FOR FASTEST "BUTT BOARDER"--
THAT'S WHAT THEY CALL IT--
AT 65 MILES AN HOUR.
AND HE WROTE
THE BOOK ON THE SUBJECT:
 E STREET LUGE SURVIVAL GUIDE.
SO HE KNOWS A THING OR TWO
ABOUT VELOCITY.
YOU KNOW, DARREN,
PEOPLE THINK YOU'RE
NUTS, RIGHT?
I MEAN, IT'S ALSO
GOT TO BE A LITTLE
DANGEROUS, YES?
WELL, SORT OF THE IRONY IS
IS THAT STREET LUGE
OR LAY DOWN SKATEBOARDING,
VELOPED
TO TRY TO GO DOWN HILLS
IN A SAFER WAY ON A SKATEBOARD.
SO WE'VE GOT THE GEAR,
THE ROLLING GEAR
THAT'LL HANDLE IT.
WE DRESS IN LEATHE.
SO WE'RE SORT OF SET UP FOR
A ROAD RACING MOTORCYCLE CRASH.
IF YOU USE THE PROPER EQUIPMENT,
IT CAN BE VERY SAFE.
IT'S STILL NOT
FOR YOUR, UH
BASIC GOLFER
TYPE, IS IT?
I LIKE GOLF.
TELL ME
WHAT'S THE FASTEST
A LUGE CAN GO?
WE, ON MOST RACECOURSES
THE SPEEDS DON'T GET MUCH OVER
60 MILES AN HOUR.
AT'S BECAUSE THE ROADS
ARE TWISTY MOUAIN ROADS
WHERE YOU HAVE TO BREAK;
YOU'RE SLIDING
TO GET THROUGH THE TURNS.
UH, THE VERY FASTEST
ON THE RACING CIRCUIT
GOES A LITTLE OVER
70 MILES AN HOUR.
BUT ON A FAIRLY STRAIGHT ROAD
THE GUINNESS WORLD RECORD WAS
SET AT 81½ MILES AN HOUR.
WOW. DO YOU THINK
TH RECORD
WILL EVER BE BROKEN?
OH, ABSOLUTELY.
MAYBE, MAYBE NOT.
WE KNOW THAT WHEN WE DROP
SOMETHING
GRAVITY PULLS ITOWN, RIGHT?
THAT'S CALLED ACCELERATION
DUE TO GRAVITY
AND... IT'S GOT A NUMBER.
THANKS TO ISAAC NEWTON,
WE KNOW THAT AN OBJECT
ACCELERATES BY
9.METERS PER SECOND
EVERY SECOND
THAT IT'S IN THE AIR.
SO, THE HIGHER UP
I DROP SOMETHING
THE LONGER IT FALLS
AND THE FAST IT WILL GO.
THAT MAKES SENSE, RIGHT?
( grunting )
SO, LET'S SAY I DROPPED
A BASEBALL
FROM UP HERE AT 5,000 FEET...
BY THE TIME THE BALL GETS HE,
IT'S GOING
ABOUT 95 MILES PER HOUR.
OOH!
THAT'S ABOUT AS FAST
AS A BIG LEAGUE PITCH.
'S FAST, BUT NOT THAT FAST.
BUT LES SAY I DROPPED
A BASEBALL FROM WAY  HERE
AT 10,000 FEET...
 giggles )
FROM 10,000 FEET, THE BALL WILL
BE TRAVELING ABOUT...
95 MILES PER HOUR.
BUT HOW IS THAT POSSIBLE?
IF GRAVITY IS ACCELERANG
THE BALL 9.8 METERS PER SECOND
FOR EVERY SECOND THAT IT'S
IN THE AIR
A BALL TRAVELING FROM
10,000 FEET WILL BE FALLING
A LOT LONGER THAN A BALL
FROM 5,000 FEET.
HOW CAIT BE GOING
THE SAME SPEED?
OKAY, T WHAT ABOUT
ISAAC NEWTON?
I MEAN, HOW CAN THE BALL
END UP AT THE SAME SPEED?
NEWTON WAS TALKING ABOUT OBJECTS
FALLING IN A VACUUM
LIKE IN OUTER SPACE
OR SOMETHING.
IS IT BECAUSE
OF T AIR?
AH, WHAT ABOUT THE AIR?
WELL, THERE'S
AIR RESISTANCE.
YEAH, AND WHAT DO WE CALL
AIR RESISTAN?
"DRAG."
DRAG SLOWS TNGWN.
LIKE THIS SIGN IS CATCHING
SO MUCH AIR
I'M HARDLY MOVING AT ALL.
I GOT TO GET NEW SPONSOR.
ANY OBJECT PASSING
THROUGH A FLUID
EXPERIENCES DRAG.
SEE, AIR IS A FLUID
WHEN IT COMES TO PHYSICS.
IF I DROP THIS BALL
IT EXPERIENCES DRA
THROUGH THE AIR
BUT IT'S SO MINIMAL,
IT'S HARD TO SEE.
BUT IN THE WATER
 IT'S EASY TO SEE
 THE EFFECT OF DRAG.
 WATER IS DENSER THAN AIR.
BUT HERE'S THE IMPORTANT PART:
 THE WATER SLOWS THE LL UNTIL
 IT FINALLY REACHES A SPEED
 WHERE IT STOPS ACCELERATING.
 EVENTUALLY, IT SINKS
 AT A CONSTANT SPEED.
 THAT SPEED IS A GOLF BALL'S
 TERMINAL VELOCITY IN WATER.
OKAY, SO THIS IS ALL
PRETTY OBVIOUS, RIGHT?
IT'S LIKE IF I DROP A FEATHER.
IT ACCELERATES
FOR A REALLY SHORT TIME.
THEN IT REACHES
A CONSTANT SPEED.
TERMINAL VELOCITY.
WHY DOES IT REACH TERMINAL
VELOCITY SO QUICKLY?
IT HAS TO DO WITH ITS WEHT
COMPARED TO ITS SURFACE AREA.
RIGHT.
BECAUSE A FEATHER,
COMPED TO ITS WEIGHT
HAS A RELATIVELY
LARGE SURFACE AREA.
Marissa:
 WHEN AN OBJECT
 FIRST STARTS FALLING
 ITS SPEED ISN'T FA ENOUGH
 FOR DRAG TO BE A MAJOR FACTOR.
 SO IT ACCELETES,
 GOES FASTER AND FASTER.
 BUT, AS IT GOES FASTER,
 THE DRAG FORCE INCREASES
 UNTIL IT REACHES
 A POINT WHERE IT EQUALS
 THE FORCE OF GRAVITY
 PULLING THE WEIGHT DOWN.
 THIS RESULTS IN AN EQUILIBRIUM
 WHERE THE JECT
 STOPS ACCELERATING.
 IT WON'T FALL ANY FASTER.
 IT'S REACHED TERMINAL VELOCITY.
SO WHAT ABOUT
A HEAVIER OBJECT
WITH A SMALLER
SURFACE AREA
KE A LUGE?
A HEAVIER OBJECT
WITH THE SAME OR
LESSER SURFACE AREA
WILL FALL FASTER TN
THE LIGHTER ONE.
BUT EVERYTHING HAS
A TERMINAL VELOCITY.
IT'LL JUST BE
A LITTLE FASTER.
IF WE IGNORE AIR RESISTANCE
AG, OR IF IT'S SO SMALL
THAT IT'S REALLY
NOTHING TO WORRY ABOUT
THEN ALL OBJECTS
FALL AT THE ME RATE.
BUT IF DRAG IS A FACTOR--
LIKE WITH THIS VOLLEYBALL
AND THIS BASKETBALL...
THEY BOTH HAVE ABOUT THE SAME
SUACE AREA
BUT THE BASKETBALL
WEIGHS A LOT MORE.
LOOK.
 THE BASKETBALL
 IS FALLING FASTER.
 BECAUSE OF ITS GREATER WEIGHT
 IT HAS TO GO FASTER
 BEFORE THERE'S ENOUGH DRAG
 TO EQUAL GRATY'S PULL.
OKAY, DARREN,
SO YOU GUYS WANT TO PRESENT
AS LITTLE SURFACE AREA
TO THEIR AS POSSIBLE.
SO, WHAT DO YOU GUYS DO?
IN ORDER TO BE FASTER
YOU'VE GOT TO GET YOUR
FEET TUCKED DOWN LOW
GOT TO GET
YOUR ELBOWIN
AND YOUR HEAD
AS LOW AS POSSIBLE.
ALL RIGHT.
WHEN WE LOOK AT DRAG...
WE USEN EQUATION
THAT LOOKS LIKE THIS:
"D," DRAG FORCE, EQUALS "K,"
CONSTANT..
UH, NOW, I KNOW THAT CONSTANT
BEGINS WITH A "
BUT IN PHYSICS,
WE USE A "K," OKAY?
AND WE'RE GOING TO TALK MORE
ABOUT E CONSTANT LATER
BUT FOR NOW,
YOU JUST NEED TO KNOW
THAT IT'S A MBER
THAT REMAINS THE SAME.
IT'S CONSTANT.
TIMES "A," AREA,
TIMES, "" VELOCITY.
AND IT'SQUARED.
NOW THAT "SQUARED"
IS A REALLY BIG DEAL.
THE SURFACE AREA THAT DARREN
PRESENTS TO THE AIR
LOOKS LIKE THIS.
SO, DARREN, YOU DON'T HAVE
A LOT OF SURFACE AREA
TO SLOW YOU DOWN.
BUT WE HAVE
A LOT OF SPEED
AND THAT ENDS UP
SLOWING US DOWN.
RIGHT, IS
KIND OF WEIRD, RIGHT?
BUT YOUR SPEED ACTUALLY
SLOWS YOU DOWN
MORE THAN
THE SURFACE AREA.
BUT HOW CAN SPEED SLOW YOU DOWN?
 THE FASTER THEUGE GOES,
 THE GREATER THE NUMBER
 OF AIR MOLECULES IT ENCOUNTERS.
 AND THE GREATER THE FORCE
 OF THE AIR'S IMPACT.
 THAT'S WHY VELOCITY SQUARE
 IS SUCH A BIG THING.
 IT MEANS THAT IF YOUR
 VELOCITY DOUBLES, AG FORCE
 QUADRUPLES.
 AND IF YOUR VELOCITY TRIPLES
 THE DRAG FORCE INCREASES
 BY A FACTOR OF NINE.
SO, THE FASTER YOU GO,
THE MORE EFFECT DRAG HAS ON YOU.
AND ITEEPS GROWING AND GROWING
UNTIL DRAG'S FORCE
EQUALS GRAVITY'S FORCE
ON YOUR WEIGHT
AND YOU STOP ACCELERATING.
SO, DARREN,
BESIDES DRAG
WHAT HAS THE GREATEST EFFECT
ON YOUR TERMINAL VELOCITY?
THE WEIGHT
OF THE OBJECT.
SO WOULD THE HEAVIEST RIDER
WITH THE HEAVIEST BOARD
HAVEHE GREATEST
TERMINAL VELOCITY?
NOT NECESSARILY.
A HEAVIER RIDER
IS PROBABLY BIGGER
AND PRESENTS A LARGER
SURFACE AREA TO THE WIND.
ALSO, THE EXTRA WEIGHT
CAUSES THE WHEELS
TO DEFORM AGAINST THE ROAD
WHICH CREATES MORE FRICTION.
RIGHT, THE ROAD.
BUT, AT THE
HIEST SPEEDS
THIS SPORT'S ALL ABOUT WIND.
OKAY, SO FOR
OUPURPOSES
LES JUST DEAL
WITH AIR FRICTION.
OKAY, SO WHAT ABT
THIS "K"
THE CONSTANT IN
OUR EQUATION?
AT'S THAT ALL ABOUT?
I'LL GIVE YOU A HINT.
PART OF IT IS THE LEATHER
A LUGER WEARS.
AT COULD BE
THE SURFACE DRAG.
HOW SMOOTH OR ROUGH
THE SURFACE IS
THAT THE AIR PASSES OVER?
RIGHT, PART OF OUR CONSTANT
IS THE DRAG COEFFICIENT.
THAT'S THE NUMBER THAT SAYS
HOW EALY AIR
PASSES OVER A SURFACE.
LIKE, SAY YOU WENT LUGING
IN THIS OUTFIT.
THE RRY SURFACE WOULD HAVE A
WAY HIGHER COEFFICIENT OF DRAG
THAN THE SMOOTH SURFACE
OF LEATHERS.
OKAY, WHAT ELSE
COULD MAKE UP
THIS CONSTANT
SIDES THE SURFACE?
WHAT ELSE AFFECTS
DRAG FORCE?
I'LL GIVE YOU A HINT.
WATER.
THE DENSITY OF THE AIR?
RIGHT.
BUT AIR'S
JUST AIR.
NOT SO.
AIR DOESN'T SEEM VERY DENSE
UNLESS YOU THINK OF IT
AS COMPAD TO SPACE
WHERE THERE IS NO AIR.
THEN IT REALLY DOES SEEM A LOT
CLOSER TO WATER IN THICKNESS.
ON EARTH, THE AIR'S DENSITY
CHANGEA LOT
FROM PLACE TO PLACE.
OUT HERE AT SEA LEVEL,
THE AIR IS A LOT HEAVIER
A T DENSER PER VOLUME THAN
IT WOULD BE UP ITHE MOUNTAINS.
YOU KNOW HOW IT'S HARDER
TO BREATHE UP IN THE MOUNTAINS?
THAT'S BECAUSE
THE AIR IS LESS DENSE.
SO IF YOU'RE
LUGING UP IN THE MOUNTAINS
YOU CAN HAVE
A HIGHER TERMINAL VELOCITY.
ALSO, AIR TEMPERATURE
AFFECTS AIR DENSITY A LOT.
COLDER AIR
IS MUCH DENSER THAN WARMER AIR.
SO, A HOT DAY IN THE MOUNTNS
IS GOING TO BE
YOUR FASTEST LUGE RUN.
WITHOUT ATMOSPHERE OR FRICTION
THERE IS NO
TERMINAL VELOCITY IN SPACE.
WELL, ACTUALLY THERE IS--
THE SPEED OF LIGHT.
BUT THAT'S A WHOLE OTHER TOPIC.
SO WHEN DO WE FIGURE OUT
DARREN'S TERMINAL VELOCITY
WELL, SEE, BECAUSE
OF THE CPLEXITIES
OF THE DRAG COEFFICIENT
AND THE AIR DENSITY
FIGURING OUT THE EXACT
TERMINAL VELOCITY
IS A LITTLE COMPLICATED
FOR US TO GO INTO RIGHNOW.
BUT WE CAN
TAKE A LOOK AT HOW IT WORK
( screaming )
WHOA.
TERMINAL VELOCITY
IS WHERE GRAVITY'S FORCE
EQUALS DRAG FORCE, RIGHT?
IN AN EQUATION,
IT LOOKS LIKE THIS:
MY MASS TIMES GRAVITY
EQUALS DRAG FORCE.
SO, TO SOLVE FOR VELOCITY
WE NEED TO DIVIDE
BOTH SIDES BY "kA"
TO GET "mg" DIVIDED BY "kA"
EQUALS VELOCITY SQUAD.
SO, TERMINAL VELOCITIS THE
SQUARE ROOT OF GRAVITY FORCE
DIVIDED BY kA.
A SKYDIVER
IN THIS POSITION PRESENTS
ABOUT THE SAME SURFACE AREA
AS A LUGER.
MY TERMINAL VELOCITY WILL REH
ABOUT 200 MILES PER HOUR
IN TEN TO 15 SECONDS.
IF I DIDN'T PULLY CHUTE CORD
THAT'S THE SAME SPEED I WOULD BE
GOING ALL THE WAY TO THE GROUND.
IN THAT CASE, IT REALLY
WOULD BE TERMINAL VELOCITY.
SO, DARREN, COULD
A STREET LUGE
GO 200 MILES
PER HOUR?
THERE'S A LOT
OF REASONS
WHY IT COULDN'T
BE THAT FAST.
SO, BASED
ON WHAT WE KNOW
WHAT IS THE TERMINAL
VELOCITY FOR STREET LUGE?
WITH THE CURRENT TECHNOLOGY
ON RACING LUGES TODAY
PROBABLY NOT MUCH FAER
THAN IN THE HIGH 80s.
IF YOU ADD SOME
AERODYNAMIC AIDES
SOME DIFFERENT WHEELS
YOUR PUSHING UP INTO THAT
90-MILE-AN-HR REGION
BUT THE HOLY GRAIL
FOR THE STREET LUGERS
SEEMS TO BE
100 MILES AN HOUR.
100 MILES PER HOUR.
THAT'S FAST.
 BRINGS UP ANOTHER EQUATION
WE HAVEN'T TALKED ABOUT
WHICH IS,
"I" EQUALS "V" TO THE "H."
OH, REALLY?
WHAT'S THE "I"?
INERTIA?
INJURY.
INJURY, OH.
AND "V" ST
BE VELOCITY.
WHAT'S THE "H"?
THAT'S THE HOSPITAL FACTOR.
A CRASH THATOU HAVE
ON YOUR SKATEBOARD
AT 20 MILES AN HOUR
IN FRONT OF YOUR HOUSE
SKINS YOU UP AND WILL
MAKE Y SORE FOR A MONTH.
AT SIXTY...
YOU'RE IN TRACTION.
IT'S BAD
OH, MAN.
OKAY, GUYS,
SO WT HAVE WE LEARNED?
THAT ALL OBJECTS
FALLING THROUGH A MEDIUM
WILL HAVE A TERMINAL VELOCITY.
AND THAT VELOCITY
IS DETERMINED BYRAG.
WHEN DRAG FORCE EQUALS
THE PULL OF GRAVITY
THE WEIGHT OF ANBJECT
IT STOPS ACCELERATING.
AND DRAG FORCE IS DETERMINED
BY SURFACE AREA AND VELOCITY.
BUT FIGURING OUT TERMINAL
VECITY IS REALLY COMPLICATED.
COMPLICATE YES, BUT VERY
IMPORTANT IF YOU WANT  WIN.
WHOO!
 IF YOU WANT TO GET FURTHER
 INTO TERMINAL VELOCITY
 VISIT OUR WEB SITE
 AT sportsfigures.espn.com.
WELL, THAT'S IT.
WE'D LIKE TO THANK
 DARREN LOTT...
WHOA.
AND OUR STUDENTS
FROM CARLSBAD HIGH--
 ANDY, DUSTY, LYLA AND EMILY--
FOR HELPING US OUT HERE TODAY
ON ESPN'S SPORTS FIGURES--
"TERMINAL VECITY."
OF COURSE YOU KNOW,
THIS IS ALL AN ILLUSION.
( laughing )
