JOAN CARTAN-HANSEN, HOST: WE

CAN'T SEE IT, BUT WE FEEL ITS

EFFECTS.

IT IMPACTS EVERYTHING IN THE

UNIVERSE. IT'S GRAVITY.

COME DOWN TO EARTH AND LEARN

MORE...

(MUSIC)

CARTAN-HANSEN: GRAVITY IS THE

FORCE OF ACTION BETWEEN TWO

OBJECTS, IN THIS CASE BETWEEN

THE MELONS AND THE EARTH.

IN THE LATE 1600, SIR ISAAC

NEWTON SAW AN APPLE FALL FROM A

TREE.

(THUMP, THUMP)

THAT MADE HIM

WONDER IF THE FORCE THAT MADE

THE APPLE FALL

(MORE THUMPING)

WAS THE SAME FORCE THAT KEPT THE

PLANETS IN ORBIT AROUND THE SUN.

NEWTON CHANGED THE WAY WE ALL

LOOK AT GRAVITY.

CARTAN-HANSEN: TO TALK ABOUT

GRAVITY, YOU FIRST HAVE TO TALK

ABOUT MASS AND MATTER.

NOW MATTER TAKES UP SPACE AND

HAS MASS.

AND MASS IS A MEASUREMENT OF HOW

MUCH MATTER SOMETHING HAS.

THE MORE SOMETHING WEIGHS, THE

MORE MASS IT HAS AND THE MORE

GRAVITY PULLS ON IT.

BUT THE EARTH'S GRAVITATIONAL

PULL IS STRONG BECAUSE IT IS SO

MUCH MASS.

THE GREATER THE MASS OF THE

OBJECT, THE GREATER THE FORCE OF

GRAVITY.

ASTRONAUTS COULD BOUNCE EASILY

ON THE MOON BECAUSE THE MOON'S

GRAVITY IS LESS THAN THE

EARTH'S...BECAUSE THE MOON HAS

LESS MASS THAN THE EARTH.

STUDENT: DOES THAT MEAN I WEIGH

A DIFFERENT AMOUNT ON DIFFERENT

PLANETS?

CARTAN-HANSEN: WELL ON EARTH

SUPPOSE YOU WEIGH 100 POUNDS.

IF YOU WERE ON THE MOON, YOU'D

WEIGH ABOUT 17 POUNDS.

BUT, IF YOU WERE ON A BIGGER

PLANET, SAY, JUPITER, YOU'D

WEIGH MORE THAN A WHOPPING 236

POUNDS.

AND GRAVITY'S AFFECT DEPENDS ON

HOW CLOSE OBJECTS ARE TO ONE

ANOTHER.

THE EARTH'S GRAVITATIONAL PULL

ON SAY, PLUTO, ISN'T VERY STRONG

BECAUSE PLUTO IS SO FAR AWAY.

BUT THE EARTH'S GRAVITATIONAL

PULL ON THE MOON IS GREAT.

THE EARTH'S GRAVITY KEEPS THE

MOON IN ORBIT.

STUDENT: SO IF EARTH'S GRAVITY

IS SO STRONG, HOW DO ASTRONAUTS

GET INTO SPACE AND WHY DO THEY

JUST FLOAT THERE?

CARTAN-HANSEN: ASTRONAUTS CAN

TAKE OFF FROM THE EARTH BECAUSE

THE THRUST EXERTED BY THE POWER

OF THE ROCKET IS GREATER THAN

THE FORCE OF GRAVITY PULLING

THEM DOWN.

BUT ASTRONAUTS NEVER TRAVEL

BEYOND THE EARTH'S GRAVITATIONAL

PULL.

AND THEY ACTUALLY AREN'T REALLY

FLOATING.

THEY ARE, IN FACT, ALWAYS

FALLING TOWARD EARTH.

BUT SINCE THEY ARE ALSO MOVING

FORWARD, THEY FALL AROUND THE

EARTH IN A CIRCLE OR AN ORBIT.

TO THE ASTRONAUTS, THIS CONSTANT

STATE OF FALLING JUST FEELS LIKE

FLOATING.

IT'S CALLED A STATE OF

WEIGHTLESSNESS OR ZERO GRAVITY.

THESE BOISE STATE UNIVERSITY

ENGINEERING STUDENTS ARE FLYING

IN A SPECIAL AIRPLANE THAT CAN

CREATE MOMENTS OF

WEIGHTLESSNESS.

STUDENTS: "WHOO!" "ZERO G"

CARTAN-HANSEN: THEY ARE

STUDYING THE EFFECTS OF MICRO

GRAVITY ON THE TRACTION OF

DIFFERENT WHEEL TREAD DESIGNS ON

LUNAR SOIL AND THEY'RE ALSO

TESTING WAYS TO FIND OUT HOW

MUCH WATER THERE IS IN THE SOIL

ON THE MOON OR OTHER PLANETS.

STUDENTS: "BEST FEELING IN THE

WORLD!"

CARTAN-HANSEN: GRAVITY AFFECTS

EVERYTHING ON EARTH, INCLUDING

THE EARTH.

GRAVITY FROM THE MOON PULLS AT

OUR OCEANS CAUSING HIGH TIDE AND

LOW TIDE.

GRAVITY PULLS WATER FROM THE

CLOUDS CAUSING RAIN AND SNOW.

GRAVITY TUGS AT ROCKS, CAUSING

SIMPLE LOOSE ROCKS TO MOVE OR

WHOLE HILL SIDES TO SLIDE DOWN.

EVEN STARS AND PLANETS ARE

FORMED WHEN GRAVITY PULLS DUST

AND OTHER SMALL PARTICLES

TOGETHER.

SO, GRAVITY IS ONE OF THE

FUNDAMENTAL FORCES IN NATURE.

STUDENT: OOPS!

CARTAN-HANSEN: WHOA, YOU OKAY?

STUDENT: YEA.

WHAT GOES UP MUST COME DOWN.

IT'S JUST GRAVITY.

JOAN: IF YOU WANT TO LEARN MORE

ABOUT GRAVITY AND OTHER

SCIENTIFIC TOPICS, CHECK OUT THE

SCIENCE TREK WEBSITE.

YOU'LL FIND IT AT

IDAHOPTV.ORG/SCIENCE TREK

(MUSIC)

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IDAHO NATIONAL LABORATORY,

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FRIENDS OF IDAHO PUBLIC

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