( sighs )
( whistling )
WHOA...
( groans )
WHOA...
WHOA...
WHOA... WHOA...
MOMMY...!
A BODY PARTIALLY OR WHLY
IMMERSED IN A FLUID
IS BUOYED UP BY A FORC..
EQUAL TO THE WEIGHT
OF THE FID IT DISPLACES.
( grunts )
UH... THAT'S, UH...
THAT'S WHY THIS LIFE VEST
KEEPS  AFLOAT
AND, UH, THAT'S WHY, UH...
WHY THAT THERE KAYAK FLOATS.
IN FACT, THAT'S
WHY ANYTHING THAT FLOATS, UH...
FLOATS.
( squeaking )
THIS GUY PADDLING IN
BACK BEHIND ME HERE
IS ADAM BOYD.
NOW ADAM IS 18
AND HE FINISHED
IN THE TOP TEN
OF THE MEN'S U.S.
OLYMPIC TRIALS
FINISHED SECOND OVERALL
IN THE C-1 COMPETION
AT THE POTOMAC
WHITE-WATER FESTIVAL...
AND RECENTLY, ADAM WAS
DOWN IN AGUA AZUL, MEXICO
WHERE HE CAME ACROSS
 POSTCARD FALLS,
 A 55-FOOT WATERFALL.
HOWDY.
HOW'S IT GOING?
PRETTY GOOD.
SO DID YOU SUFFER
ANY BODILY DAMAGE
GOING OVERHAT WATERFALL?
NOPE. I WAS ALL RIGHT.
NO BROKEN BONES
OR COLLAPSED LUNGS?
NO. NO PROBLEM.
THAT'S GOOD.
THAT'S GOOD TO HEAR.
SO TELL US LITTLE BIT
ABOUT THIS HERE KAYAK.
WELL, THIS IS
A DAGGER KAYAK.
IT'S MADE OUT OF PLASTIC.
IT'S HOLLOW THROUGHOUT,
FILLED WITH AIR.
AND IS HERE, WE HAVE
WHAT WE CALL A SPRAY SKI.
IT KEEPS THE AIR IN
AND THE WATER T.
SO YOU DO GO
UNDERWATER SOMETIMES.
 LIKE, SAY YOU GO OVER FALLS
 OR YOU'RE IN THE RAPIDS...
IT WILL GO UNDER, YEAH.
THE WATER WILL PUSH
 YOU UNDER, BUT THEY'RE DESIGNED
 TO BRING YOU RIGHT BACK UP
 TO THE SURFACE.
SO THIS BABY HERE,
THIS BABY RIGHT HE
THIS FLOATS PRETTY
GOOD, RIGHT?
ITLOATS REALLY GOOD.
THIS FLOATS REALLY GOOD.
JUST THAT TINY LITTLE KAYA
SUPPORTS ITSELF AND ADAM.
WHY?
WHY DOES THIS PIE PLATE FLOAT...
AND THIS ONE...
SINK?
THE ANSWER IS
"SPECIFIC GRAVITY."
SPECIFIC GRAVITY IS
HOW WE FIGURE OUT
WHETHER SOMETHING IS GOING
TO FLOAT OR T
AND HOW MUCH WEIGHT WE CAN
PUT ON IT BEFORE IT SINKS.
( grunts )
NOW LET'S START
WITH DISPLACEMENT.
 IF WE DIG A HOLE
IN THE GROUND
WHAT HAVE  DONE?
LL, WE'VE DISPLACED THE DIRT.
THERE USED TO BE DIRT HERE,
AND NOW THERE'S NOT.
NOW THERE'S A HOLE.
THAT'S DISPLACENT.
SO, UH... LET'S SEE
IF WE CAN TRY TO DIG A HOLE...
IN THE WATER.
YOU CAN'T DO IT, RIGHT?
THE WATER KEEPS
RUSHING BACK IN.
RIGHT.
BECAUSE OF THE FLUID
NATURE OF LIQUID
WH YOU DISPLACE IT
THLIQUID WANTS TO PUSH
BACK IN TO THAT AREA.
IT'S OKAY, THOUGH.
THE WATER PUSHING BACK IN
HAS A FORCE.
WEALL IT...
THE "BUOYANT FORCE."
NOW THE BUOYANT FORCE
IT WHAT MAKES SOMETHING FLOAT.
( groans )
BUT THERE ACTUALLY IS A WAY
TO DIG A HOLE IN WATER.
( high-pched whistle )
DID YOU EVER NOTICE
WHAT HAPPENS TO A BATHTUB
WHEN YOUILL IT ALL THE WAY
TO THE TOP AND GET IN?
THIS...
IS BECAUSE THE SPACE
MY BODY IS TAKING UP
USED TO BE FILLED WITH WATER.
BY GETTING IN, I'VE DISPLACED
AN AMOUNT OF WATER
EQUAL TO THE VOLUME OF SPACE
MY BODY IS TAKING UP.
I'VE CREATED A HOLE
IN THE WATER.
NOW, THE MORE SPACE
WE TAKE UP IN THE WATER...
CO ON, EVERYBODY!
AH.
THE MORE WATER WE DISPLACE.
I JUST WANT TO SAY
I FEEL SO MUCH LOVE
IN THIS POOL RIGHT NOW.
OKAY, EVERYBODY OUT.
NOW ECK IT OUT.
WHEN I GOT IN,
THIS POOL WAS FULL.
LOOK HOW MUCH WATER
WE'VE DISPLACED
JUST BY THE VOLUME
OF ALL OF OUR BODIES.
WHEN YOU GO INTO A RIVER
YOU' DISPLACING
AN AMOUNT OF WATER
EQUAL TO THE WEIGHT
OF YOUR BODY
SO THE RIVER LEVEL RISES
BYHAT MUCH.
BECAUSE MY BODY, UH,
AND THIS LIFE VEST
MADE A HOLE IN THE WATER
AND BECAUSE THE WATER WANTS
TO PUSH BACK INTO THAT HOLE
THE BUOYANT FORCE IS EQUAL
TOHE WEIGHT OF THE WATER
I'M DISPLACING.
 IF WE COLLECTED
 THE WATER I DISPLACED
 WHEN I GOT INTO THE POOL
 AND WEIGHED IT
 WEOULD HAVE A FIGURE
 FOR THE BUOYANT FORCE
 THE WATER WAS EXERTING ON ME.
SO, UM, HOW MUCH
ES WATER WEIGH?
WELL, LET'S FIND OUT.
UH... WE COULD USE...
WELL, A CUBIC FOOT OF WATER
WEIG ABOUT 62 POUNDS.
OH, WAIT A SECOND.
EXCUSE ME. "ABOUT"?
WHAT'S THIS
"ABOUT" STUFF?
WE NEED TO BE
EXACT HERE, EXACT.
WELL, THE WATER'S DENSITY
DEPENDS ON LOT OF STUFF
LIKE IF IT'S SALTWATER
OR FRESHWATER
EVEN THE TEMPERATURE.
BUT A GOOD AVERAGE TO USE
IS 62 POUNDS PER CUBIC FOOT.
OKAY. WOW.
WELL, THEN THAT MEANS
THIS RIVER MUST WEIGH...
A LOT.
( splat )
( groaning )
JUST KIDDING.
I'M FINE.
I'M FINE, RELY.
ALL RIGHT. THAT'S GOOD.
SO, YOU SEE, WHETHER
SOMETHING FLOATS OR NOT
DOESN'T HAVE ANYTHING TO DO
WITH HOW MUCH IT WEIGHS
BUT EVERYTHING TO DO
WITH HOW MUCH THE FLUID
IT DISPLACES WEIGHS.
YOU SEE, THIS COCONUT HERE
WEIGHS MORE
THAN THIS ROCK, BUT...
THE COCONUT WILL FLOAT
EVEN THOUGH IT WEIGHS MORE.
( squeaking )
OKAY, HERE'S HOW IT WORKS.
ALL RIGHT, ARE YOU READY?
REY BACK THERE?
ALL RIGHT.
THESE TWO PIE PLATES
ARE EXACTLY THE SAME.
THE ONLY DIFFERENCE IS THIS.
WHEN I PLACE THIS IN THE WATER
IT DISPLACES SOME OF THE WATER.
GRAVITY IS PULLING
THE PIE PLATE DOWN
BUT THE WATER  PUSHING BACK
WITH A BUOYANT FORCE
EQUAL TOHE WEIGHT
OF THE WATER DISPLACED.
IF THE WEIGHT
OF THE WATER DISPLACED
ISN'T GREAR THAN THE WEIGHT
OF THE OBJECT, IT SINKS.
BUT... BUT... BUT...
BUT... BUT... BUT... BUT...
 IF WE INCREASE THE AMOUNT
 OF WATER DISPLACED
 THE FORCE PUING BACK
 AGAINST THE OBJECT IS INCREASED
 AND ITLOATS, EVEN THOUGH
 IT WEIGHS THE ME
 AND IS MADE
 OF THE SAME MATERIAL
 AS THE PIE PLATE THAT SUNK.
 THAT'S ARCHIMEDES' PRINCIPLE.
SO WE END  WITH A RATIO
BETWEEN THE WEIGHT OF AN OECT
AND THE WEIG
OF THE FLUID IT DISPLACES
AND THIS RATIO IS CALLED
"SPECIFIC GRAVITY.
( groans )
NOW, IF AN OBJECT HAS
A ECIFIC GRAVITY
OF LESS THAN ONE, IT WILL FLOAT.
IF IT'S GREAR THAN ONE,
IT SINKS.
OKAY, SO LET'S FIGURE OUT
WHY THIS PUPPYLOATS.
ALL RIGHT, THEN.
OKAY, OKAY, GOOD.
SO FIRST THING WE GOT TO DO
IS FIGURE OUT
HOW MUCH WATER
THIS KAYAKS GOING TO
DISPLACE, SO LET'S START
BY FIGURING OUT
THE DIMENSIONS
OF THE PART OF THE KAYAK
THAT'S IN THE WATER, OKAY?
ALL RIGHT.
ALL RIGHT, GOOD.
LET'S GET A LITTLE
MEASUREMENT HERE.
SO, UH, DO YOU
WANT A TAPEREDUT
WITH THIS BABY?
SOUNDS GREAT.
WE CAN P SOME WINGS ON
IT FOR YOU IF YOU WANT.
OKAY.
COULD YOU HOLD
IS FOR ME?
I'LL BE BACK
IN JUST A SECOND.
YEAH.
ALL RIGHT, 42, PERFECT.
ALL GHT,
THAT LOOKS GOOD.
YOU OKAY?
YEAH.
OKAY, COOL.
 THE PART OF THE YAK
 THAT'S UNDERWATER
 IS FIVE FEET LONG
 BY TWO FEET WIDE
 BY SIX INCHES DEEP.
 TO FIND THE VOLUME,
 WE JUST MULTIPLY.
 THAT GIVES US FIVE CUBIC FEET.
 HOW MUCH DOES
THIS KAYAK WEIGH?
ABOUT 40 POUNDS.
ALL RIGHT, ALL RIGHT,
AND HOW MUCH DO YOU WEIGH?
A HUNDRED AND FIFTY.
ALL RIGHT, OKAY
SO THAT MEANS
THE YAK HAS TO DISPLACE
AT LEAST 190 POUNDS TO FLOAT.
OKAY,  IF WE HAVE
FIVE CUBIC FEET
AT 62 POUNDS
PER CUBIC FOOT
THAT'S... SEVEN... ( mumbling )
310 POUNDS OF BUOYANT FORCE,
WHICH  A RATIO OF...
( mumbling )
.61, WHICH IS
LESS THAN WATER.
SO THIS KAYAK WILL FLOAT
WITH YOU IN IT.
WELL, I ALREADY
KNEW THAT.
BUT YOU DIDN'T KNOW WHY.
 A KAYAK IS BASICALLY
 A SEALED CONTAINER.
 AS LONG AS IT MAINTAINS ITS
 VOLUME OF AIR INSIDE THE HULL
 IT'S GOING TO HAVE
 A SPECIFIC GRAVITY
 THAT WILL KEEP IT COMING
 BACK UP TO THE SURFACE.
HEY, GREG, HOW COME FI
DON'T FLOAT OR SINK?
WELL, I'M GLAD
YOU ASKED, COURTNEY.
YOU SEE, FISH HAVE SOMHING
WE CALL "NEUTRAL BUOYANCY."
 BECAE THE WEIGHT
 OF THE WATER THEY DISPLACE
 IS ROUGHLY EQUAL
 TO THEIR OWN WEIGH
 THEY DON'T SINK OR FLOAT.
THAT'S WHY SCUBA DIVERS
WEAR WEIGHBELTS.
TO CANCEL OUT
THEIR NATURAL BUOYANCY
THEY ADD WEIGHT
TIL THEY'RE NEUTRAL.
HERE, GREG, CAN YOU
HOLD THIS FOR A SEC?
OH, YEAH, YEAH, SURE.
I HAD A LDFISH
THAT FLOATED ONCE.
HE WAS DEAD.
OH. OKAY.
WELL, WE'RE NOT
ACTUALLY TALKING
ABOUT DEAD GOLDFISH
TODAY, BUT, BUT, THANKS.
THANKS FOR SHARING.
 SHIPS ARE MADE
 OFRETTY HEAVY MATERIALS:
 EEL, EVEN CONCRETE.
 THE REASON THEY FLOAT
 IS THE AIRSPACE INSIDE THE HULL
 TAKES UP VOLUME
 AND THAT MAKES SURE
 THE SPECIFIC GRAVITY
 IS LESS THAN ONE.
 IF THE HULL SPRINGS A LEAK
 THE AIR IS REPLACEBY WATER,
 WHICH IS HEAVY
 AND IT FILLS
 UNTIL THE SPECIFIC GRAVITY
 IS GREATER THAN ONE
 AND IT SINKS.
ARE WE ROLLING? OKAY.
HI. I'M JO KAZIMIERCZYK,
OWNER OF MILLBROOK BOATS.
I DESIGN AND BUILD WHITE-WATER
CANOES AND KAYAKS.
Greg:
HOW MUCH
SOMEONE WEIGHS
HOW DOES THAT AFFECT
THE CONSTRUCTION
OF THE BOAT?
THE FASTEST BOATS
ARE THE NARROWEST BOATS.
UNFORTUNATELY,
FOR A HEAVIER RSON
THAT MIGHT NOT BE TRUE
SO A HEAVIER PERSON
HAS TO GET HIS BUOYANCY
FROM SOMEWHERE ELSE.
THE KAYAK MIGHT
BE MADE DEEPER
THE DEPTH
OF THE BOAT...
Greg:
UH-HUH.
WOULD MAKE UP
THE BUOYANCY
IN THE VERTICAL PLANE
RATHER THAN THE WIDTH.
RIGHT.
THE HORIZONTAL PLANE.
SO, JOHN, THE OLD
ARCHIMEDES' PRINCIPLE
MUST BE PRETTY
IMPORTANT TO YOU.
IT'S CERTAINLY THE FOCAL POINT
OF A BOAT BUILDER, YEAH.
WITHOUT IT, YOU'D BE SUNK.
( laughs )
WHO SAID THAT?
SO THAT'S IT.
I'D LIKE TO ANK ADAM BOYD...
AND THE REST OF THE KAYAKERS
WHO HELPED US TODAY:
COURTN...
BRENDAN...
SILAS AND KYLE...
WELL...
I'D ALSO LIKE TO THANK
PETER KENNEDY
AND BILL FARLEY
FROM ADVENTURE QUEST.
NOW, I DON'T KNOW,
I MAY GO OUT ON A LIMB HERE
BUT I'D VENTURE  SAY
THAT OUR, UH...
OUR SPECIFIC GRAVITY
I THINK, UH...
I THINK IT'S ME THAN ONE.
WHAT DO YOU GUYS THINK?
Kayakers:
YEAH.
I THINK IT'S MORE THAN ONE.
WE'RE T GOING ANYWHERE.
 [Captioning sponsored by THE
 U.S. DEPARTMENT OF EDUCATION]
