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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