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,
AUDREY STAPLES.

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YOU MIGHT HAVE HEARD THE SAYING
THAT OPPOSITES ATTRACT.

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AND, YOU KNOW, THAT'S TRUE
IN A LOT OF CASES,

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LIKE IN SOME
BAD ROMANTIC COMEDIES

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OR WHEN YOU BRING A PAIR
OF MAGNETS CLOSE TO EACH OTHER.

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NORTH AND SOUTH POLES
WILL SNAP TOGETHER.

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BUT SOMETIMES,
LIKE WITH WATER,

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MOLECULES OF THE SAME SUBSTANCE
ATTRACT.

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WONDER WHY?

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YOU'LL GET A BETTER PICTURE
OF WHY

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WHEN YOU GET THE CHANCE
TO SEE WATER

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SOMEPLACE OTHER THAN EARTH,

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LIKE ON THE INTERNATIONAL
SPACE STATION,

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COMMONLY REFERRED TO
AS THE ISS,

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WHERE WATER APPEARS TO BE
NEARLY WEIGHTLESS.

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HERE'S CANADIAN SPACE AGENCY
ASTRONAUT BOB THIRSK

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ON THE ISS

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WITH A CLOSER LOOK AT WATER
AND THIS SPECIAL PROPERTY.

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- THE INTERMOLECULAR FORCES

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CAUSE WATER TO BE ATTRACTED
TO ITSELF,

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WHICH IS CALLED COHESION.

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FOR EXAMPLE,
HERE ARE TWO SPHERES OF WATER.

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WHEN THE SPHERES
ARE SEVERAL CENTIMETERS APART,

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THERE'S NO ATTRACTIVE FORCES
BETWEEN THEM.

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BUT WHEN I BRING THEM CLOSE
ENOUGH TOGETHER TO ATTRACT,

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THEY MERGE THROUGH THEIR
ATTRACTIVE FORCES.

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- SO YOU PROBABLY ALREADY KNOW

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THAT WATER MOLECULES
ARE ATTRACTED

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TO OTHER WATER MOLECULES,

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AND THAT'S CALLED COHESION.

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WELL, THESE SAME COHESIVE FORCES

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ARE RESPONSIBLE
FOR SURFACE TENSION.

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SURFACE TENSION
IS THE PROPERTY OF A LIQUID

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THAT MAKES IT BEAD UP
WHEN IT DRIPS ON A SURFACE,

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LIKE A LEAF OR YOUR SKIN
OR A COIN.

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WATER'S SURFACE TENSION
IS PRETTY STRONG.

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YOU CAN CHECK IT OUT

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WITH AN EYEDROPPER OF WATER
AND A PENNY.

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TAKE A CLOSER LOOK.

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SEE WHAT HAPPENS
WHEN YOU SQUEEZE THE WATER OUT

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ONTO THE PENNY,
ONE DROP AT A TIME.

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HOW MANY DROPS DO YOU THINK

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YOU CAN GENTLY SQUEEZE
ONTO THE PENNY

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BEFORE THE WATER SPILLS
OVER THE SIDE OF THE PENNY?

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I BET IT'LL BE MORE
THAN YOU EXPECTED.

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SURFACE TENSION IS WHAT ALLOWS
THE WATER DROPS

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TO CLING TOGETHER,

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FORMING THAT DOME OR BULGE
AT THE TOP.

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YOU CAN SEE
THAT WATER'S SURFACE TENSION

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IS PRETTY STRONG.

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YOU CAN ALSO SEE
THE COHESION OF THE WATER

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AS IT STUCK TO ITSELF.

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BUT THE WATER
DID SOMETHING ELSE AS WELL:

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IT STUCK TO THE PENNY TOO.

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WHY WAS THAT?

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HERE'S BOB AGAIN TO EXPLAIN

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AND TO SHOW HOW IT WORKS
IN SPACE.

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- INTERMOLECULAR FORCES
CAN ALSO CAUSE WATER

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TO BE ATTRACTED
TO OTHER MATERIALS.

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THIS IS CALLED ADHESION.

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FOR EXAMPLE,
WATER CAN STICK TO A STRAW.

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WHEN I MOVE THE STRAW
CLOSE TO THE SPHERE,

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THE WATER STICKS.

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WATER STICKS TO MANY OTHER
MATERIALS AS WELL.

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THINK ABOUT ALL THE THINGS
ON EARTH

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THAT YOU SEE
LITTLE WATER DROPS ON:

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WINDOWS, TREE LEAVES,

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EVEN YOUR OWN SKIN.

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LET ME SHOW YOU WITH MY HAND.

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THE MOLECULES ON MY SKIN
WILL PULL HARD ENOUGH

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TO MAKE THE WATER STICK.

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THE WATER TRIES
TO FIND A BALANCE

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BETWEEN THE COHESION
WITH THE WATER

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AND THE ADHESION TO MY HAND.

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EVENTUALLY IT SETTLES
ON AN UNUSUAL SHAPE

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THAT FILLS THE SPACE
BETWEEN MY FINGERS.

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IF I CONTINUE
BY ADDING WATER,

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I CAN EVENTUALLY BUILD
AN ENTIRE GLOVE OF WATER

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THAT WILL STAY FIXED
TO MY HAND.

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IT STICKS TO MY HAND
BY INTERMOLECULAR FORCES.

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HOW COOL IS THAT?

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- YOU KNOW,
IF IT WEREN'T FOR GRAVITY,

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SUBTLE FORCES LIKE
SURFACE TENSION, COHESION,

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AND ADHESION
MIGHT HAVE A LOT BIGGER IMPACT

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ON OUR EVERYDAY LIVES
ON EARTH.

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WOULD WE STILL USE BOWLS,
SPOONS, AND CUPS?

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OR WOULD WE COME UP
WITH NEW TOOLS

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THAT WOULD MAKE OUR LIVES
EASIER?

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WELL, THAT'S SOMETHING
TO THINK ABOUT

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AS WE PLAN TO EXPLORE PLACES
LIKE THE MOON, MARS, AND BEYOND.

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THAT'S IT FOR NOW.

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I'M AUDREY STAPLES,

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AND WE'LL CATCH YOU NEXT TIME
ON "NASA LAUNCHPAD."