WEBVTT

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[dramatic percussion music]

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- HEY, EVERYBODY,
WELCOME TO "NASA LAUNCHPAD."

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I'M YOUR HOST, SCOTT BEDNAR.

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DO YOU KNOW WHO THIS GUY IS?

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WELL, YOU SHOULD.
THAT'S SIR ISAAC NEWTON.

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YOU MAY HAVE HEARD OF THE STORY
OF AN APPLE FALLING ON HIS HEAD,

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LEADING TO A GREATER
UNDERSTANDING OF GRAVITY.

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THAT STORY MAY NOT BE
ENTIRELY TRUE, THOUGH.

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THE APPLE MAY NOT HAVE
REALLY HIT HIM ON THE HEAD.

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BUT ONE THING THAT IS TRUE
IS THAT NEWTON'S LAWS OF MOTION

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HAVE A HUGE IMPACT
ON EVERYTHING WE DO.

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NOT FAMILIAR
WITH NEWTON'S LAWS OF MOTION?

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WELL, LET'S RUN THROUGH THEM
VERY QUICKLY IN SIMPLE TERMS.

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AND HEY, YOU CAN TRY THIS
AT HOME.

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CENTER AN INDEX CARD
OVER THE TOP OF A GLASS

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AND PUT A COIN IN THE MIDDLE
OF THE CARD, LIKE SO.

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THEN CAREFULLY FLICK THE CARD
TO ONE SIDE.

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COOL, THE COIN DROPPED
RIGHT DOWN INTO THE GLASS.

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NOW PUT THE COIN
ON A FLAT SURFACE AND WAIT.

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STILL WAITING?

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NOTICE THAT THE COIN
JUST SITS THERE.

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IT IS NOT MOVING ANYWHERE
BY ITSELF.

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YOU HAVE JUST WITNESSED
FIRSTHAND NEWTON'S FIRST LAW:

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OBJECTS TEND TO KEEP ON DOING
WHATEVER THEY'RE DOING--

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STAYING AT REST
OR STAYING IN MOTION--

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UNLESS SOMETHING ELSE
EXERTS A FORCE ON THEM.

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OF COURSE, THAT'S NET FORCE.

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THINK OF IT THIS WAY.

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IF TWO GUYS
ARE TRYING TO MOVE A COUCH

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AND ONE OF THEM PUSHES
IN ONE DIRECTION

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AND ONE PUSHES
IN THE OTHER DIRECTION,

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THE TWO FORCES ARE BALANCED
AND CANCEL EACH OTHER OUT.

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THE COUCH DOESN'T MOVE,

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AND IT IS THE SAME
AS NO FORCE AT ALL.

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BUT IF A THIRD GUY COMES UP
AND JOINS ONE SIDE,

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YOU WOULD HAVE A NET FORCE,

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SOMETHING LEFT OVER
WHEN YOU FIGURE OUT

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ALL THE FORCES
ACTING ON SOMETHING.

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YOU CAN'T JUST
ADD UP THE NUMBERS

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TO SEE IF THERE IS
A NET FORCE.

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DIRECTION IS IMPORTANT TOO.

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WE'LL COME BACK TO THAT.

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NOW ON TO LAW TWO:

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AN NET FORCE
ACTING ON AN OBJECT

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CAUSES THE OBJECT
TO ACCELERATE.

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WE'D BETTER GO BACK
AND FIGURE OUT

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WHAT ACCELERATION IS FIRST.

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ACCELERATION IS ANY CHANGE

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IN AN OBJECT'S SPEED
OR DIRECTION.

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THE ACCELERATION DEPENDS
ON THE AMOUNT OF FORCE APPLIED

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AND THE MASS
OF THE OBJECT BEING MOVED.

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WHEN YOU ADD LOTS OF FORCE
TO AN OBJECT,

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IT ACCELERATES MORE THAN IF
YOU ADD LESS FORCE TO AN OBJECT.

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ONCE AGAIN.
MAKES SENSE, DOESN'T IT?

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AND FINALLY, LAW THREE:

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WHEN AN OBJECT EXERTS A FORCE
ON ANOTHER OBJECT,

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THE SECOND OBJECT EXERTS

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AN EQUAL AND OPPOSITE FORCE
BACK.

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NEED MORE INFO?

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LET'S HEAD TO
THE INTERNATIONAL SPACE STATION,

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WHERE IT'S ACTUALLY EASIER

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TO OBSERVE NEWTON'S LAWS
IN ACTION.

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HERE'S ASTRONAUT DAN TANI
WITH SOME DEMONSTRATIONS.

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- LET'S PRETEND
LIKE I'M ON THE GROUND

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IN YOUR CLASSROOM.

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AND IF I WERE TO TAKE ONE
OF THESE CANDY-COATED CHOCOLATES

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AND LET GO OF IT,
WHAT WOULD HAPPEN?

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WELL, IT WOULD GO CRASHING
ONTO THE GROUND, WOULDN'T IT?

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AND THEN WHEN I ATE IT,
IT WOULD HAVE TO BE

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A DIRTY CHOCOLATE
THAT FELL ON THE GROUND.

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THE REASON THAT HAPPENS TO YOU
IN A CLASSROOM OR ON THE GROUND

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IS, THERE'S A FORCE
EXERTED ON THE CHOCOLATE,

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AND THAT FORCE IS PROVIDED
BY GRAVITY, OKAY?

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AND THAT FORCE IS ALWAYS
STRAIGHT DOWN.

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SO IF YOU WERE TO DROP
THE CANDY-COATED CHOCOLATE,

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IT WOULD FALL TO THE GROUND

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BECAUSE IT HAS A FORCE
IMPOSED ON IT.

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BUT HERE IN THE SPACE STATION
AND IN LOW-EARTH ORBIT,

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WE ARE UNDER MICROGRAVITY,

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WHICH IS ESSENTIALLY NO GRAVITY,
NO APPARENT GRAVITY.

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SO IF I LET GO OF THE CANDY...

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IT DOESN'T FALL.

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IT STAYS AT REST

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BECAUSE THERE'S NO
EXTERNAL FORCE ON IT, OKAY?

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ACTUALLY, THERE'S A LITTLE FORCE
BECAUSE WE HAVE FANS GOING,

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AND SO THE FORCE
IS PROVIDED BY THE AIRFLOW.

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BUT BASICALLY,
THERE'S NO FORCE ON IT

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UNTIL AN EXTERNAL FORCE
IS IMPOSED ON IT...

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LIKE THAT.

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- NEWTON'S FIRST LAW
ONLY MAKES SENSE

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IF YOU THINK ABOUT ALL OF
THE FORCES AFFECTING AN OBJECT.

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IF YOU THROW A BALL
HERE ON EARTH,

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PRETTY QUICKLY,
IT STOPS MOVING, RIGHT?

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SO WHAT OTHER FORCES
ARE AT WORK?

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GRAVITY PULLS THE BALL
TOWARDS EARTH.

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FRICTION IS A RESISTING FORCE

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CAUSED WHEN OBJECTS
RUB AGAINST EACH OTHER.

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THESE FORCES ARE ACTING
AGAINST THE FIRST FORCE,

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YOU THROWING THE BALL.

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SO A BATTLE OF FORCES
IS TAKING PLACE.

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EVENTUALLY, THE FORCES
BALANCE EACH OTHER OUT,

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AND EQUILIBRIUM IS ESTABLISHED,

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SO THE BALL RETURNS TO REST,

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OR STOPS MOVING
ALTOGETHER.

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ALL RIGHT, BACK TO DAN
FOR THE SECOND LAW.

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- "F" EQUALS "MA."

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THAT'S A PRETTY SIMPLE
EQUATION,

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BUT IT REALLY MEANS A WHOLE LOT

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TO PEOPLE WHO STUDY
HOW THINGS MOVE.

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AND LET'S DO
A LITTLE DEMONSTRATION

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OF "F" EQUALS "MA."

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I'M DOWN HERE ON THE FLOOR
OF THE SPACE STATION,

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OR WE CALL IT THE DECK.

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WE HAVE SOME BUNGEES SET UP.

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BUNGEES HOLD OUR STUFF DOWN.

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BUT A BUNGEE'S A GOOD WAY
TO IMPOSE

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A PARTICULAR AMOUNT OF FORCE
ON THINGS.

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LET'S PUT THIS CANDY
UNDER A LITTLE BIT OF FORCE

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AND SEE WHAT HAPPENS.

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THE FORCE
THAT THE BUNGEE EXERTED

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EQUALS THE MASS,
WHICH IS SMALL,

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TIMES THE ACCELERATION
THAT IT EXPERIENCED, OKAY?

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SO BIG ACCELERATION,
LITTLE MASS

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FOR THE SAME AMOUNT OF FORCE,
OKAY?

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SO FORCE,
FORCE IS EQUAL TO "MA."

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SO LET'S NOW--LET'S DO THAT,

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PUT THAT FORCE
ON THE OLD HAMMER.

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THERE, YOU SEE THAT?

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A LOT LESS ACCELERATION.

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SO THE FORCE IS THE SAME.

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THE FORCE FROM THE BUNGEE
WAS THE SAME,

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BUT THE MASS WAS REALLY SMALL
FOR THE CHOCOLATE.

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IT EXPERIENCED
A BIGGER ACCELERATION,

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SO IT GOT A BIGGER--
A FASTER SPEED.

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BUT THE BIGGER MASS,
SAME AMOUNT OF FORCE,

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RESULTED IN A SLOWER
ACCELERATION.

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- SO IF YOU'VE GOT THE SAME
FORCE ACTING ON TWO OBJECTS,

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THE MASS AND ACCELERATION
OF THE OBJECTS

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ARE INVERSELY PROPORTIONAL.

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IT'S ALGEBRA.

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BIGGER "M," SMALLER "A."

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BIGGER "A," SMALLER "M."

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AND NOW FOR THE GRAND FINALE,
NEWTON'S THIRD LAW.

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AND HERE'S DAN AGAIN
WITH A BIG BAG OF WATER

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TO SHOW HOW IT WORKS.

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- OKAY, SO WHAT HAPPENED THERE?

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I PUSHED AWAY THE WATER,

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AND I WAS--I LIFTED MY FEET
SO I WAS FLOATING.

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AND IT WENT AWAY
WITH THE SPEED,

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AND I WENT AWAY
WITH THE SPEED,

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BECAUSE WHEN I PUSHED,

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THAT ACTION HAD AN EQUAL
AND OPPOSITE REACTION ON ME.

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SO THE FORCE
THAT WE PUSHED THE WATER OFF,

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I USED THE SAME FORCE
TO PUSH MYSELF BACK, OKAY,

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BUT I WENT SLOWER BECAUSE
I HAVE MORE MASS THAN THE WATER.

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AND THIS IS HOW ROCKETS WORK.

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WHAT ROCKETS DO IS,
THEY THROW OUT THEIR PROPELLANT.

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PROPELLANT IS REALLY HEAVY.

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ALL THAT MASS GETS USED

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TO PROPEL THE SHUTTLE
INTO ORBIT.

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AND WHAT IT DOES IS,

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THE ROCKET ENGINES
CREATE COMBUSTION,

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AND IT SPITS OUT
THE MASS OF THAT PROPELLANT

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OUT THE BACK OF THOSE ENGINES,
AND THAT MASS PUSHES--

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AND THAT FORCE
PUSHES THE SHUTTLE INTO SPACE,

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AND THAT'S HOW ROCKETS WORK.

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- SO A ROCKET CARRIES FUELS
WHICH EXPLODE AND MIX TOGETHER.

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THE GASES
FROM THE CONTROLLED EXPLOSIONS

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ARE FORCED OUT
OF THE REAR OF THE ROCKET

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AT A REALLY HIGH SPEED.

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THE LARGE MASS OF GAS
IS PUSHED BACK

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AGAINST THE SMALLER MASS
OF THE ROCKET,

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AND THE ROCKET
ACCELERATES FORWARD.

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NEWTON'S THIRD LAW IN ACTION.

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FROM CARD TRICKS TO
THE INTERNATIONAL SPACE STATION,

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NEWTON'S LAWS HELP US
UNDERSTAND AND EXPLAIN

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PRINCIPLES OF MOTION.

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YOU WANT TO FIND OUT MORE?

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WELL, VISIT NASA'S
TEACHING FROM SPACE WEBSITE

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AT THE ADDRESS ON YOUR SCREEN.

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THAT'S ALL FOR THIS EPISODE.

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UNTIL NEXT TIME,
I'M SCOTT.

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CATCH YOU NEXT TIME
ON "NASA LAUNCHPAD."