[dramatic percussion music]
- HEY, WELCOME TO "NASA LAUNCHPAD."
I'M YOUR HOST, AUDREY STAPLES.
YOU MIGHT HAVE HEARD THE SAYING THAT OPPOSITES ATTRACT.
AND, YOU KNOW, THAT'S TRUE IN A LOT OF CASES,
LIKE IN SOME BAD ROMANTIC COMEDIES
OR WHEN YOU BRING A PAIR OF MAGNETS CLOSE TO EACH OTHER.
NORTH AND SOUTH POLES WILL SNAP TOGETHER.
BUT SOMETIMES, LIKE WITH WATER,
MOLECULES OF THE SAME SUBSTANCE ATTRACT.
WONDER WHY?
YOU'LL GET A BETTER PICTURE OF WHY
WHEN YOU GET THE CHANCE TO SEE WATER
SOMEPLACE OTHER THAN EARTH,
LIKE ON THE INTERNATIONAL SPACE STATION,
COMMONLY REFERRED TO AS THE ISS,
WHERE WATER APPEARS TO BE NEARLY WEIGHTLESS.
HERE'S CANADIAN SPACE AGENCY ASTRONAUT BOB THIRSK
ON THE ISS
WITH A CLOSER LOOK AT WATER AND THIS SPECIAL PROPERTY.
- THE INTERMOLECULAR FORCES
CAUSE WATER TO BE ATTRACTED TO ITSELF,
WHICH IS CALLED COHESION.
FOR EXAMPLE, HERE ARE TWO SPHERES OF WATER.
WHEN THE SPHERES ARE SEVERAL CENTIMETERS APART,
THERE'S NO ATTRACTIVE FORCES BETWEEN THEM.
BUT WHEN I BRING THEM CLOSE ENOUGH TOGETHER TO ATTRACT,
THEY MERGE THROUGH THEIR ATTRACTIVE FORCES.
- SO YOU PROBABLY ALREADY KNOW
THAT WATER MOLECULES ARE ATTRACTED
TO OTHER WATER MOLECULES,
AND THAT'S CALLED COHESION.
WELL, THESE SAME COHESIVE FORCES
ARE RESPONSIBLE FOR SURFACE TENSION.
SURFACE TENSION IS THE PROPERTY OF A LIQUID
THAT MAKES IT BEAD UP WHEN IT DRIPS ON A SURFACE,
LIKE A LEAF OR YOUR SKIN OR A COIN.
WATER'S SURFACE TENSION IS PRETTY STRONG.
YOU CAN CHECK IT OUT
WITH AN EYEDROPPER OF WATER AND A PENNY.
TAKE A CLOSER LOOK.
SEE WHAT HAPPENS WHEN YOU SQUEEZE THE WATER OUT
ONTO THE PENNY, ONE DROP AT A TIME.
HOW MANY DROPS DO YOU THINK
YOU CAN GENTLY SQUEEZE ONTO THE PENNY
BEFORE THE WATER SPILLS OVER THE SIDE OF THE PENNY?
I BET IT'LL BE MORE THAN YOU EXPECTED.
SURFACE TENSION IS WHAT ALLOWS THE WATER DROPS
TO CLING TOGETHER,
FORMING THAT DOME OR BULGE AT THE TOP.
YOU CAN SEE THAT WATER'S SURFACE TENSION
IS PRETTY STRONG.
YOU CAN ALSO SEE THE COHESION OF THE WATER
AS IT STUCK TO ITSELF.
BUT THE WATER DID SOMETHING ELSE AS WELL:
IT STUCK TO THE PENNY TOO.
WHY WAS THAT?
HERE'S BOB AGAIN TO EXPLAIN
AND TO SHOW HOW IT WORKS IN SPACE.
- INTERMOLECULAR FORCES CAN ALSO CAUSE WATER
TO BE ATTRACTED TO OTHER MATERIALS.
THIS IS CALLED ADHESION.
FOR EXAMPLE, WATER CAN STICK TO A STRAW.
WHEN I MOVE THE STRAW CLOSE TO THE SPHERE,
THE WATER STICKS.
WATER STICKS TO MANY OTHER MATERIALS AS WELL.
THINK ABOUT ALL THE THINGS ON EARTH
THAT YOU SEE LITTLE WATER DROPS ON:
WINDOWS, TREE LEAVES,
EVEN YOUR OWN SKIN.
LET ME SHOW YOU WITH MY HAND.
THE MOLECULES ON MY SKIN WILL PULL HARD ENOUGH
TO MAKE THE WATER STICK.
THE WATER TRIES TO FIND A BALANCE
BETWEEN THE COHESION WITH THE WATER
AND THE ADHESION TO MY HAND.
EVENTUALLY IT SETTLES ON AN UNUSUAL SHAPE
THAT FILLS THE SPACE BETWEEN MY FINGERS.
IF I CONTINUE BY ADDING WATER,
I CAN EVENTUALLY BUILD AN ENTIRE GLOVE OF WATER
THAT WILL STAY FIXED TO MY HAND.
IT STICKS TO MY HAND BY INTERMOLECULAR FORCES.
HOW COOL IS THAT?
- YOU KNOW, IF IT WEREN'T FOR GRAVITY,
SUBTLE FORCES LIKE SURFACE TENSION, COHESION,
AND ADHESION MIGHT HAVE A LOT BIGGER IMPACT
ON OUR EVERYDAY LIVES ON EARTH.
WOULD WE STILL USE BOWLS, SPOONS, AND CUPS?
OR WOULD WE COME UP WITH NEW TOOLS
THAT WOULD MAKE OUR LIVES EASIER?
WELL, THAT'S SOMETHING TO THINK ABOUT
AS WE PLAN TO EXPLORE PLACES LIKE THE MOON, MARS, AND BEYOND.
THAT'S IT FOR NOW.
I'M AUDREY STAPLES,
AND WE'LL CATCH YOU NEXT TIME ON "NASA LAUNCHPAD."