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JOAN CARTAN-HANSEN, HOST: WE

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CAN'T SEE IT, BUT WE FEEL ITS

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EFFECTS.

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IT IMPACTS EVERYTHING IN THE

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UNIVERSE. IT'S GRAVITY.

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COME DOWN TO EARTH AND LEARN

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MORE...

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(MUSIC)

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CARTAN-HANSEN: GRAVITY IS THE

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FORCE OF ACTION BETWEEN TWO

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OBJECTS, IN THIS CASE BETWEEN

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THE MELONS AND THE EARTH.

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IN THE LATE 1600, SIR ISAAC

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NEWTON SAW AN APPLE FALL FROM A

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TREE.

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(THUMP, THUMP)

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THAT MADE HIM

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WONDER IF THE FORCE THAT MADE

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THE APPLE FALL

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(MORE THUMPING)

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WAS THE SAME FORCE THAT KEPT THE

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PLANETS IN ORBIT AROUND THE SUN.

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NEWTON CHANGED THE WAY WE ALL

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LOOK AT GRAVITY.

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CARTAN-HANSEN: TO TALK ABOUT

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GRAVITY, YOU FIRST HAVE TO TALK

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ABOUT MASS AND MATTER.

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NOW MATTER TAKES UP SPACE AND

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HAS MASS.

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AND MASS IS A MEASUREMENT OF HOW

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MUCH MATTER SOMETHING HAS.

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THE MORE SOMETHING WEIGHS, THE

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MORE MASS IT HAS AND THE MORE

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GRAVITY PULLS ON IT.

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BUT THE EARTH'S GRAVITATIONAL

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PULL IS STRONG BECAUSE IT IS SO

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MUCH MASS.

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THE GREATER THE MASS OF THE

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OBJECT, THE GREATER THE FORCE OF

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GRAVITY.

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ASTRONAUTS COULD BOUNCE EASILY

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ON THE MOON BECAUSE THE MOON'S

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GRAVITY IS LESS THAN THE

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EARTH'S...BECAUSE THE MOON HAS

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LESS MASS THAN THE EARTH.

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STUDENT: DOES THAT MEAN I WEIGH

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A DIFFERENT AMOUNT ON DIFFERENT

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PLANETS?

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CARTAN-HANSEN: WELL ON EARTH

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SUPPOSE YOU WEIGH 100 POUNDS.

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IF YOU WERE ON THE MOON, YOU'D

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WEIGH ABOUT 17 POUNDS.

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BUT, IF YOU WERE ON A BIGGER

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PLANET, SAY, JUPITER, YOU'D

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WEIGH MORE THAN A WHOPPING 236

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POUNDS.

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AND GRAVITY'S AFFECT DEPENDS ON

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HOW CLOSE OBJECTS ARE TO ONE

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ANOTHER.

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THE EARTH'S GRAVITATIONAL PULL

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ON SAY, PLUTO, ISN'T VERY STRONG

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BECAUSE PLUTO IS SO FAR AWAY.

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BUT THE EARTH'S GRAVITATIONAL

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PULL ON THE MOON IS GREAT.

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THE EARTH'S GRAVITY KEEPS THE

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MOON IN ORBIT.

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STUDENT: SO IF EARTH'S GRAVITY

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IS SO STRONG, HOW DO ASTRONAUTS

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GET INTO SPACE AND WHY DO THEY

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JUST FLOAT THERE?

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CARTAN-HANSEN: ASTRONAUTS CAN

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TAKE OFF FROM THE EARTH BECAUSE

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THE THRUST EXERTED BY THE POWER

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OF THE ROCKET IS GREATER THAN

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THE FORCE OF GRAVITY PULLING

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THEM DOWN.

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BUT ASTRONAUTS NEVER TRAVEL

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BEYOND THE EARTH'S GRAVITATIONAL

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PULL.

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AND THEY ACTUALLY AREN'T REALLY

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FLOATING.

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THEY ARE, IN FACT, ALWAYS

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FALLING TOWARD EARTH.

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BUT SINCE THEY ARE ALSO MOVING

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FORWARD, THEY FALL AROUND THE

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EARTH IN A CIRCLE OR AN ORBIT.

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TO THE ASTRONAUTS, THIS CONSTANT

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STATE OF FALLING JUST FEELS LIKE

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FLOATING.

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IT'S CALLED A STATE OF

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WEIGHTLESSNESS OR ZERO GRAVITY.

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THESE BOISE STATE UNIVERSITY

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ENGINEERING STUDENTS ARE FLYING

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IN A SPECIAL AIRPLANE THAT CAN

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CREATE MOMENTS OF

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WEIGHTLESSNESS.

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STUDENTS: "WHOO!" "ZERO G"

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CARTAN-HANSEN: THEY ARE

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STUDYING THE EFFECTS OF MICRO

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GRAVITY ON THE TRACTION OF

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DIFFERENT WHEEL TREAD DESIGNS ON

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LUNAR SOIL AND THEY'RE ALSO

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TESTING WAYS TO FIND OUT HOW

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MUCH WATER THERE IS IN THE SOIL

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ON THE MOON OR OTHER PLANETS.

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STUDENTS: "BEST FEELING IN THE

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WORLD!"

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CARTAN-HANSEN: GRAVITY AFFECTS

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EVERYTHING ON EARTH, INCLUDING

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THE EARTH.

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GRAVITY FROM THE MOON PULLS AT

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OUR OCEANS CAUSING HIGH TIDE AND

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LOW TIDE.

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GRAVITY PULLS WATER FROM THE

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CLOUDS CAUSING RAIN AND SNOW.

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GRAVITY TUGS AT ROCKS, CAUSING

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SIMPLE LOOSE ROCKS TO MOVE OR

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WHOLE HILL SIDES TO SLIDE DOWN.

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EVEN STARS AND PLANETS ARE

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FORMED WHEN GRAVITY PULLS DUST

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AND OTHER SMALL PARTICLES

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TOGETHER.

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SO, GRAVITY IS ONE OF THE

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FUNDAMENTAL FORCES IN NATURE.

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STUDENT: OOPS!

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CARTAN-HANSEN: WHOA, YOU OKAY?

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STUDENT: YEA.

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WHAT GOES UP MUST COME DOWN.

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IT'S JUST GRAVITY.

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JOAN: IF YOU WANT TO LEARN MORE

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ABOUT GRAVITY AND OTHER

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SCIENTIFIC TOPICS, CHECK OUT THE

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SCIENCE TREK WEBSITE.

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YOU'LL FIND IT AT

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IDAHOPTV.ORG/SCIENCE TREK

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(MUSIC)

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NARRATOR: PRESENTATION OF

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SCIENCE TREK ON IDAHO PUBLIC

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TELEVISION IS MADE POSSIBLE

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THROUGH THE GENEROUS SUPPORT OF

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00:04:05,633 --> 00:04:06,966
THE LAURA MOORE CUNNINGHAM

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FOUNDATION, COMMITTED TO

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FULFILLING THE MOORE AND BETTIS

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FAMILY LEGACY OF BUILDING THE

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GREAT STATE OF IDAHO; BY THE

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IDAHO NATIONAL LABORATORY,

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MENTORING TALENT AND FINDING

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SOLUTIONS FOR ENERGY AND

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SECURITY CHALLENGES; BY THE

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FRIENDS OF IDAHO PUBLIC

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TELEVISION; AND BY THE

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CORPORATION FOR PUBLIC

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BROADCASTING.