WEBVTT

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[dramatic percussion music]

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- HEY, WELCOME
TO "NASA LAUNCHPAD."

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I'M YOUR HOST,
VINCE WHITFIELD.

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HEY, YOU WANT TO SEE
SOMETHING REALLY COOL?

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CHECK THIS OUT.

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YEP, THAT'S A PAPER CLIP.

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AND IT'S NOT SINKING.

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BUT WAIT.
HOW IS THAT POSSIBLE?

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THE PAPER CLIP'S MORE DENSE
THAN WATER,

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AND WE KNOW THAT IF THE DENSITY
OF AN OBJECT

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IS GREATER THAN THE DENSITY
OF WATER,

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THE OBJECT WILL SINK, RIGHT?

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SO WHY IS THE PAPER CLIP
FLOATING?

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THIS DEMO WORKS
BECAUSE OF A PROPERTY

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KNOWN AS SURFACE TENSION.

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AND SURFACE TENSION
IS ALSO RESPONSIBLE

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FOR SOME PRETTY COOL TRICKS
WITH LIQUIDS IN SPACE.

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HERE'S CANADIAN SPACE AGENCY
ASTRONAUT BOB THIRSK

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TO EXPLAIN WHAT EXACTLY
IS SURFACE TENSION.

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- MOLECULES AT THE SURFACE
OF A LIQUID

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EXPERIENCE UNBALANCED
MOLECULAR FORCES.

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SINCE THEY ARE ON THE BOUNDARY,

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THE MOLECULES ARE ATTRACTED
FROM INSIDE

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BUT NOT FROM THE OUTSIDE.

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THIS CAUSES THE SURFACE
TO BEHAVE

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LIKE A STRETCHED
ELASTIC MEMBRANE.

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LIFE ON THE EARTH
IS DOMINATED BY GRAVITY.

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THINK OF THE THINGS YOU USE
EVERY DAY.

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YOU RIDE IN A CAR.

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YOU EAT WITH A SPOON.

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YOU SIT IN A CHAIR.

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YOU DRINK OUT OF A CUP.

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ALL OF THESE THINGS
INHERENTLY DEPEND ON GRAVITY.

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BUT UP HERE IN ORBIT,

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THE EFFECTS OF GRAVITY
SEEM TO DISAPPEAR.

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WITH GRAVITY
OUT OF THE PICTURE,

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OTHER FORCES START TO DOMINATE
OUR DAILY WORK.

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ONE SUCH FORCE THAT BECOMES
VERY IMPORTANT HERE IN ORBIT

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IS SURFACE TENSION.

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HERE IN SPACE, SURFACE TENSION
IS CRITICALLY IMPORTANT,

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EVEN FOR SOMETHING AS SIMPLE
AS GETTING A DRINK OF WATER.

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IF I POURED OUT THIS DRINK
OF WATER ON THE EARTH,

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GRAVITY WOULD SMUSH IT FLAT.

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BUT HERE IN ORBIT,
IT FLOATS IN MIDAIR...

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AND MAKES A PERFECT SPHERE.

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- SO YOU CAN SEE THAT THERE'S
A LOT MORE GOING ON

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WITH SURFACE TENSION
THAN JUST SINKING OR FLOATING.

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AND IT'S EASIER TO SEE

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THOSE PERFECT SPHERES
OF WATER IN SPACE.

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BUT YOU CAN SEE SPHERES
STARTING TO FORM

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IF YOU HAVE A LEAKY FAUCET
AND QUICK EYES

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OR A HIGH-SPEED CAMERA.

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THE MASS OF THE WATER HANGING
FROM THE FAUCET SLOWLY BUILDS

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UNTIL THE FORCE
BECOMES TOO STRONG

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FOR THE SURFACE TENSION
TO BIND IT TO THE FAUCET,

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AND AT THAT POINT, THE DROP
FALLS AND FORMS A SPHERE.

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IN FACT, EVEN IF THE WATER
IS COMING OUT OF THE FAUCET

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IN A STREAM RATHER THAN DROPS,

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WITH ENOUGH DISTANCE TO FALL,

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THE STREAM WILL ACTUALLY
BREAK UP INTO DROPS

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AND THEN SPHERES.

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SPHERES, SPHERES, SPHERES--

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WHAT'S SURFACE TENSION'S
FASCINATION

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WITH THE GLOBE SHAPE?

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WELL, LET'S SEND IT BACK UP
TO BOB FOR THE ANSWER.

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- SURFACE TENSION ARISES
BECAUSE OF TINY FORCES

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ACTING BETWEEN THE INDIVIDUAL
MOLECULES OF WATER.

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THESE INTERMOLECULAR FORCES
ARE LIKE TINY SPRINGS,

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CONNECTING
ALL THE H2O MOLECULES.

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IF THIS SPHERE OF WATER
IS SLIGHTLY STRETCHED

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IN ONE DIRECTION,

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THE TINY SPRINGS PULL IT BACK
TO ITS ORIGINAL SHAPE.

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THE WATER ALWAYS TRIES
TO BE IN A SPHERE,

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BECAUSE THIS WAY,
THE LITTLE SPRINGS

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ARE ALL STRETCHED
THE SAME AMOUNT.

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NONE HAVE TO WORK HARDER
THAN ANOTHER.

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TO SHARE THE WORK EVENLY,

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THE WATER TAKES THE SHAPE
OF THE LEAST SURFACE AREA,

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WHICH, FOR A FREELY FLOATING
OBJECT,

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IS A SPHERE.

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- WONDER WHY WATER
FORMS A SPHERE?

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MOLECULES IN LIQUID WATER
ARE MUTUALLY ATTRACTED

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BUT CAN SLIP AND SLIDE
PAST EACH OTHER.

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THAT'S HOW LIQUID WATER
CAN TAKE ON THE SHAPE

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OF THE CONTAINER
IT'S POURED INTO,

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SUCH AS A DRINKING GLASS.

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BUT WATER MOLECULES
AT THE SURFACE

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AREN'T MUCH ATTRACTED
TO GAS MOLECULES

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WHIZZING IN THE AIR ABOVE THEM.

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THEIR MAIN ATTRACTION

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IS TOWARDS OTHER WATER MOLECULES
IN THE GLASS.

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THE RESULT IS A TENSE,
TIGHT SURFACE,

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ALMOST LIKE A THIN, RUBBERY SKIN
ON THE WATER.

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SOME INSECTS CAN WALK
ACROSS THIS SKIN

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ON THE SURFACE OF A POND.

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THIS SURFACE TENSION IS THE KEY

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TO THE SHAPE OF WATER
SPILLED ON THE ISS.

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AS A PARCEL OF WATER
FREE-FALLS ON THE ISS,

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SURFACE TENSION PULLS THE WATER
INTO A SPHERE.

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HOW COME?

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SINCE THE PARCEL
IS A FREE-FLOATING BLOB,

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IT HAS ONE SMOOTH SURFACE
EXPOSED ON ALL SIDES.

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ALL MOLECULES ON THE SURFACE

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TEND TO BE TUGGED TOWARDS
THE CENTER OF THE DROP

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WITH EQUAL TENSION
BY THEIR FELLOW MOLECULES.

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AND SO THE BLOB OF WATER
PULLS INTO A COMPACT SPHERE,

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THE MOST EFFICIENT SHAPE
IN NATURE,

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WITH THE SMALLEST POSSIBLE
SURFACE AREA.

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OH, WE'RE ALMOST OUT OF TIME.

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WANT TO LEARN THE TRICK
WITH THE FLOATING PAPER CLIP?

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JUST PUTTING THE PAPER CLIP
ON THE WATER

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WOULD LEAD TO A SUNKEN SHIP--
I MEAN CLIP.

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BUT TRY THIS.

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RIP A PIECE OF TISSUE PAPER,

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PUT THAT ON THE WATER FIRST,

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AND THEN PUT THE PAPER CLIP
ON TOP OF IT.

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THEN CAREFULLY POKE
THE TISSUE PAPER,

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NOT THE PAPER CLIP,
UNTIL THE TISSUE SINKS.

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WITH A LITTLE PRACTICE,

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THE PAPER CLIP WILL BE LEFT
ON TOP OF THE WATER.

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NOW, WE KNOW IT'S NOT FLOATING
IN TERMS OF DENSITY,

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BUT, RATHER, IT'S BEING HELD UP
BY THE SURFACE TENSION.

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THAT'S HOW SOME WATER BUGS
CAN WALK ON WATER TOO.

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THERE'S MORE TO LEARN
ABOUT SURFACE TENSION,

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BUT THAT'S ALL THE TIME
WE HAVE FOR NOW.

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UNTIL NEXT TIME,
I'M VINCE WHITFIELD.

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THANKS FOR WATCHING
"NASA LAUNCHPAD."