NARRATOR: PRESENTATION OF SCIENCE TREK ON IDAHO PUBLIC TELEVISION IS MADE POSSIBLE THROUGH THE GENEROUS SUPPORT OF THE LAURA MOORE CUNNINGHAM FOUNDATION, COMMITTED TO FULFILLING THE MOORE AND BETTIS FAMILY LEGACY OF BUILDING THE GREAT STATE OF IDAHO.

BY THE FRIENDS OF IDAHO PUBLIC TELEVISION AND BY THE CORPORATION FOR PUBLIC BROADCASTING.

JOAN CARTAN-HANSEN: THE WORLD IS FULL OF MOTION, AND MOTION HAPPENS BECAUSE OF FORCE.

FIND OUT HOW FORCE AND MOTION MOVE YOUR WORLD.

STAY TUNED, SCIENCE TREK IS NEXT.

(MUSIC) JOAN CARTAN-HANSEN: HI, I'M JOAN CARTAN-HANSEN.

AND WELCOME TO SCIENCE TREK .

AND WELCOME TO THE DISCOVERY CENTER OF IDAHO.

FORCE IS BASICALLY A PUSH OR A PULL.

NOW, FORCES, LIKE GRAVITY, CAN AFFECT EVERYTHING.

WE HAVE SCIENTISTS STANDING BY TO ANSWER YOUR QUESTIONS ABOUT FORCE AND MOTION.

AND LATER ON IN THE SHOW WE'LL LEARN A LITTLE BIT MORE ABOUT GRAVITY.

BUT FIRST, LET'S FIND OUT ABOUT FORCE AND MOTION.

FORCE IS PRETTY SIMPLY.

IT'S BASICALLY JUST A PUSH OR A PULL.

SO A FORCE IS A CHANGE IN MOTION.

GRAVITY PULLS YOU DOWN, AND THE GROUND PUSHES YOU UP.

WHEN FORCES ARE IN BALANCE NOTHING HAPPENS, AND YOU DON'T NOTICE IT.

IT'S WHEN THEY GET OUT OF BALANCE THAT THINGS HAPPEN.

READY?

GRAVITY IS THE FORCE OF ATTRACTION BETWEEN THINGS.

IT'S WHAT MAKES THINGS FALL.

(SCREAMING) THERE ARE THREE LAWS OF MOTION DISCOVERED BY SIR ISAAC NEWTON.

AN OBJECT THAT ISN'T BEING PUSHED OR PULLED BY A FORCE EITHER STAYS STILL OR KEEPS MOVING IN A STRAIGHT LINE AT A CONSTANT SPEED.

(SCREAMING) STUDENT: WAIT A MINUTE, GRAVITY PULLED ME DOWN IN A STRAIGHT LINE.

WHY DID WE STOP?

CARTAN-HANSEN: WELL, NEWTON'S FIRST LAW IS ALL ABOUT INERTIA.

INERTIA IS AN OBJECT'S TENDENCY TO RESIST ANY CHANGE IN ITS MOTION.

A BODY AT REST STAYS AT REST.

A BODY IN MOTION STAYS IN MOTION.

IF GRAVITY WAS THE ONLY FORCE, YOU'D JUST KEEP SLIDING.

ANOTHER FORCE CALLED "FRICTION" SLOWS YOU DOWN, AND YOU STOP.

FORCES MAKE THINGS MOVE.

THE BIGGER THE FORCE OR THE LIGHTER THE OBJECT, THE GREATER THE MOTION.

SAY YOU PUSH A TOY ALONG THE STREET, IT'S PRETTY EASY BECAUSE THE TOY IS LIGHT, AND YOU CAN PUSH OR PULL WITH A LOT OF FORCE.

THE MORE FORCE, THE FASTER IT MOVES OR ACCELERATES.

STUDENT: GOOD AIM!

CARTAN-HANSEN: SAY YOU TRY TO PUSH OR PULL SOMETHING REALLY BIG, IT WOULD TAKE A LOT OF FORCE TO GET IT TO MOVE.

EVERY ACTION HAS AN EQUAL AND OPPOSITE REACTION.

FORCES ACT IN PAIRS.

WHEN THE SPACE SHUTTLE LIFTS OFF, THE BURNING GAS PUSHES OUT THE ENGINE AND LIFTS THE SHUTTLE.

WHEN YOU HIT YOUR FRIEND WITH A BUMPER CAR, THE FORCE PUSHES HIM AWAY, BUT THE FORCE OF HIS CAR PUSHES YOU BACK THE SAME AMOUNT OF FORCE.

HIT HIM SOFTLY, YOU BOTH MOVE JUST A LITTLE.

HIT HIM HARD, WOO-HOO, EQUAL AND OPPOSITE REACTION.

THE LAWS OF MOTION ARE THE BASIS FOR THE SCIENCE OF PHYSICS.

THEY APPLY TO ALL THE PARTICLES IN THE UNIVERSE FROM THE SMALLEST ATOM TO EVEN THE BIGGEST PLANETS.

EVEN THIS ROLLER COASTER.

STUDENT: STAY AT REST UNTIL ACTED ON BY AN OUTSIDE FORCE; THAT'S NEWTON'S FIRST LAW.

AND WHEN AN ENGINE PULLS THE CARS UP THE HILL, THAT'S NEWTON'S SECOND LAW.

APPLYING A FORCE MAKES AN OBJECT MOVE.

AND HOW DOES THE THIRD LAW APPLY?

CARTAN-HANSEN: AND FOR EVERY ACTION THERE'S AN EQUAL AND OPPOSITE REACTION.

FIRST WE GO UP, THEN WE GO DOWN.

AND JOINING US NOW TO ANSWER YOUR QUESTIONS ABOUT FORCE AND MOTION ARE KATHRYN DEVINE, ASSOCIATE PROFESSOR OF PHYSICS AT THE COLLEGE OF IDAHO, AND JOHN GARDNER, PROFESSOR OF MECHANICAL AND BIOMEDICAL ENGINEERING AT BOISE STATE UNIVERSITY.

THANK YOU BOTH FOR JOINING US.

KATHRYN DEVINE: THANKS FOR HAVING US.

JOHN GARDNER: HAPPY TO BE HERE.

CARTAN-HANSEN: OKAY.

LET'S GO TO YOUR QUESTIONS.

BLAKE: HI, MY NAME IS BLAKE.

I GO TO KAMIAH ELEMENTARY SCHOOL IN KAMIAH, IDAHO.

MY QUESTION IS WHAT IS FORCE AND HOW IT'S MADE?

DEVINE: SO A FORCE CAN BE THOUGHT OF AS A PUSH OR A PULL THAT MAKES SOMETHING CHANGE ITS SPEED.

SO IF YOU WANT TO SPEED SOMETHING UP, YOU HAVE TO PUSH OR PULL IT TO MAKE IT SPEED UP OR CHANGE DIRECTION.

AND THE WAY THAT A FORCE IS MADE COULD BE A VARIETY OF DIFFERENT THINGS.

YOU COULD DROP SOMETHING OFF A TABLE, AND IN THAT CASE THE FORCE OF GRAVITY OR THE GRAVITATIONAL FORCE WOULD MAKE IT SPEED UP TOWARDS THE GROUND, AND THAT WOULD MAKE IT MOVE.

WE'VE GOT OTHER TYPES OF FORCES.

THERE'S LIKE ELECTROSTATIC FORCES, LIKE STATIC ELECTRICITY THAT MIGHT SUCK YOUR HAIR TO A BALLOON.

SO THERE'S A VARIETY OF DIFFERENT TYPES OF FORCES THAT CAN MAKE SOMETHING MOVE, BUT THEY ALL ACT AS A PUSH OR PULL THAT MAKE SOMETHING CHANGE ITS DIRECTION OR SPEED UP OR SLOW DOWN.

EMILY: MY NAME IS EMILY.

I GO TO OWYHEE-HARBOR ELEMENTARY SCHOOL.

MY QUESTION IS WHY ARE NEWTON'S THREE LAWS SO IMPORTANT TO SCIENCE?

GARDNER: THAT'S A GREAT QUESTION.

AND I THINK ONE OF THE REASONS WHY THOSE LAWS ARE SO IMPORTANT IS BECAUSE NEWTON WAS OBSERVING A LOT OF THINGS AROUND HIM IN THE WORLD.

IN FACT, ALL THE SCIENTISTS AND THE NATURALISTS OF THE AGE WERE TRYING TO FIGURE OUT HOW THINGS MOVE AND WHY.

AND HE WAS ABLE TO LOOK AT ALL THESE OBSERVATIONS AND FOLD THEM TOGETHER INTO THIS SET OF RULES THAT REALLY FIT WELL TOGETHER AND FIT ALL THEIR OBSERVATIONS.

IT'S A GREAT EXAMPLE OF SCIENTIFIC THEORY AND THE SCIENTIFIC METHOD, IN ITSELF, BUT IT WAS ALSO VERY IMPORTANT IN HELPING US UNDERSTAND PLANETS AND GRAVITY AND JUST HOW THINGS MOVE INTO THE FUTURE.

HE REALLY LAID THE FOUNDATION FOR THAT.

CREIGHTON: MY NAME IS CREIGHTON.

I COME FROM OWYHEE ELEMENTARY SCHOOL.

MY QUESTION IS WHAT MAKES THIS BALL BOUNCE?

GARDNER: SO THAT'S A GREAT QUESTION.

SO WHEN YOU THROW THE BALL TO THE GROUND, YOU GIVE IT ENERGY, AND THAT ENERGY IS REFLECTED IN ITS VELOCITY.

THINK OF IT AS SPEED.

AND WHEN IT HITS THE GROUND, IT STOPS ALL OF A SUDDEN.

BUT THAT ENERGY DOESN'T GO AWAY; IT GETS ABSORBED INTO THE BALL, AND THE BALL SQUISHES UP A LITTLE BIT.

AND THEN AS SOON AS IT STOPS, THE BALL WANTS TO UNSQUISH, WANTS TO EXPAND, AND IT BOUNCES BACK UP AGAIN.

BUT IT WON'T COME BACK IN EXACTLY THE SAME WAY BECAUSE SOME OF THAT ENERGY GETS LOST IN THE MATERIAL OF THE BALL.

ALEX: HI, MY NAME IS ALEX.

I GO TO SAGLE ELEMENTARY SCHOOL.

AND MY QUESTION IS HOW BIG IS THE GRAVITATIONAL FIELD AROUND THE EARTH AND WHY?

DEVINE: ACTUALLY, A REALLY INTERESTING QUESTION BECAUSE, TECHNICALLY SPEAKING, A GRAVITATIONAL FIELD WOULD EXTEND AWAY FROM A MASS FOREVER.

AND SO EARTH'S GRAVITATIONAL FIELD WOULD EXTEND, YOU KNOW, INFINITELY OUT.

I GUESS WHAT'S INTERESTING TO PHYSICISTS OR THE WAY THAT PHYSICISTS TEND TO THINK IS HOW FAR DOES IT EXTEND UNTIL IT MATTERS.

AND SO ONCE YOU GET FAR ENOUGH AWAY FROM EARTH, THE GRAVITATIONAL FORCES AND FIELDS FROM OTHER OBJECTS, OTHER PLANETS, STARS WOULD START TO TAKE OVER AND BE MORE IMPORTANT.

AND SO LOCALLY AROUND EARTH OUR GRAVITATIONAL FIELD MATTERS A LOT.

ONCE YOU START MOVING OUT TO THE SOLAR SYSTEM, EVEN THOUGH TECHNICALLY THE FIELD, THE GRAVITATIONAL FIELD, STILL EXISTS FROM EARTH, OTHER THINGS ARE GOING TO PLAY A LARGER ROLE AND THEIR GRAVITATIONAL FIELDS WOULD MATTER MORE.

CARTAN-HANSEN: AUSTIN WOULD LIKE TO KNOW: WHY DOES SOMETHING DROP WHEN I THROW IT UP?

GARDNER: SO, AUSTIN, WHEN YOU THROW SOMETHING UP IN THE AIR IT'S -- WHATEVER THAT IS, WHETHER IT'S A BALL OR LET'S SAY IT'S A SOFTBALL, IT HAS MASS, AND THE EARTH UNDERNEATH YOUR FEET HAS MASS, AND GRAVITY ACTS BETWEEN TWO MASSES.

SO AS YOU THROW IT UP IN THE AIR, GRAVITY IS ALWAYS ACTING ON IT, AND IT'S CHANGING THE SPEED OF THE BALL AS IT MOVES UP.

AND IT'S ALWAYS TRYING TO PULL IT BACK TO THE CENTER OF THE EARTH.

SO AS THE BALL GOES UP, IT SLOWS DOWN AS THE FORCE OF GRAVITY SLOWS IT DOWN.

IT WILL EVENTUALLY GET TO ITS HIGHEST POINT AND STOP ALTOGETHER AND THEN COME BACK DOWN TOWARDS YOU.

AND IT DOESN'T GET TO THE CENTER OF THE EARTH BECAUSE THE SURFACE, YOU KNOW, THE GROUND, THE GRASS UNDER YOUR FEET, STOPS IT.

AND WHEN IT SITS THERE, GRAVITY IS STILL WORKING ON IT, BUT NOW THE EARTH DOES -- THE GRASS IS PUSHING BACK ON THE BALL AT THE SAME AMOUNT SO IT DOESN'T MOVE ANYMORE.

DEVINE: ONE OF THE REALLY INTERESTING THINGS I LIKE TO HAVE MY STUDENTS THINK ABOUT WITH WHEN YOU THROW BALLS IN THE AIR, TOO, IS THAT THE WAY THAT GRAVITY, THE FORCE OF GRAVITY WORKS IS IF YOU HAVE TWO MASSES, THEY'RE EXERTING EQUAL AND OPPOSITE FORCES ON EACH OTHER.

LIKE NEWTON'S THIRD LAW TELLS US: IF YOU HAVE A FORCE OF ONE OBJECT ON THIS OBJECT, THIS OBJECT IS GOING TO EXERT AN EQUAL AND OPPOSITE FORCE BACK.

AND SO THAT MEANS WHEN YOU THROW A BALL IN THE AIR, WHEN YOU JUMP IN THE AIR, YOU'RE ACTUALLY EXERTING AN EQUAL AND OPPOSITE FORCE BACK ON EARTH.

SO I ALWAYS ASK MY STUDENTS, "WHY IS IT THAT IT LOOKS LIKE THE BALL FALLS AND NOT EARTH JUMPING UP TOWARDS YOUR FEET?"

AND THE REASON FOR THAT IS BECAUSE OF NEWTON'S SECOND LAW, WHICH SAYS THAT IF SOMETHING HAS MORE MASS WITH THE SAME AMOUNT OF FORCE, IT ACCELERATES LESS.

SO IT'S KIND OF INTERESTING TO THINK OF YOU SITTING IN YOUR SEAT.

EARTH IS PULLING YOU DOWN, BUT YOU'RE ACTUALLY PULLING ON EARTH, TOO, WITH AN EQUAL AND OPPOSITE FORCE OF GRAVITY.

AYDEN: HI, MY NAME IS AYDEN, AND I GO TO WILLOW CREEK ELEMENTARY.

I WAS JUST WONDERING WHY A SLINKY FOLLOWS ITSELF DOWN THE STAIRS.

DEVINE: WELL, SLINKYS, LIKE EVERYTHING ELSE THAT HAS MASS, ARE AFFECTED BY EARTH'S GRAVITY.

AND SO WHEN YOU PUSH A SLINKY OFF THE STAIRS, EARTH'S GRAVITY IS GOING TO PULL THE TOP END OF THE SLINKY OVER AND CREATE THAT FORCE TO PULL THE FRONT END DOWN.

AND THEN YOU HAVE THE CONNECTION FORCE, I GUESS; THE SLINKY IS CONNECTED TO ITS BACK END.

AND SO THE FORCE OF THE SLINKY PULLING ON EACH OF ITS LINKS IS GOING TO CAUSE THE REST OF THE SLINKY TO GO.

AND THEN IF IT'S A LITTLE BIT OFF CENTER, THEN THE TIP TIPS OVER OR THE BACK TIPS OVER, AND EARTH'S GRAVITY PULLS ON THAT END, AND YOU START THE WHOLE PROCESS OVER AGAIN.

AND SO THE KEY FORCE THERE IS STILL GRAVITY.

(MUSIC) CARTAN-HANSEN: ANYTHING THAT HAS MASS HAS INERTIA.

IT ISN'T A FORCE LIKE FRICTION, AND THE ONLY WAY TO MAKE SOMETHING GO FASTER OR SLOWER IS TO PUSH OR PULL ON IT BY APPLYING A FORCE, AND THAT'S BECAUSE OF INERTIA.

THE MORE MASS AN OBJECT HAS, THE GREATER ITS INERTIA, SO IT TAKES A BIGGER FORCE TO MAKE IT MOVE.

(MUSIC) JACOB: HELLO, MY NAME IS JACOB, AND I GO TO BASIN ELEMENTARY.

THE QUESTION I WOULD LIKE TO ASK TODAY IS HOW DID OUR EARTH'S GRAVITY FORM, AND WHERE DID IT EVER CHANGE?

GARDNER: GRAVITY IS RELATED DIRECTLY TO MASS.

SO THE EARTH HAS GRAVITY BECAUSE IT HAS MASS, BECAUSE IT'S MADE UP OF STUFF, OF MATTER.

AND SO I THINK ONE OF THE ANSWERS TO THAT QUESTION IS THE SAME THING AS ANSWERING HOW DID THE EARTH FORM IN THE FIRST PLACE OR HOW DO PLANETS FORM.

AND THE PLANETS FORM BECAUSE, SAY THERE WERE A COUPLE OF SMALLER PIECES OF MASS THAT WERE ATTRACTING EACH OTHER, AND THEY CAME TOGETHER, AND THEY STUCK TOGETHER BECAUSE THAT'S WHAT GRAVITY DOES; IT PULLS OBJECTS TOGETHER.

AND SO THOSE TWO OBJECTS TOGETHER HAD MORE MASS, AND SO THEY HAD A BIGGER GRAVITATIONAL FORCE THAT THEY COULD PULL ON OTHER OBJECTS IN THE AREA.

AND SO PLANETS CAME TOGETHER AS A COALESCENT OF BRINGING TOGETHER OF A BUNCH OF SMALLER PIECES.

AND ONCE THERE WAS ENOUGH MASS THERE, THEN IT COULD ALSO START PULLING TOGETHER OTHER KINDS OF MOLECULES THAT MAKE UP GAS.

AND THAT'S HOW WE GOT AN ATMOSPHERE.

WE NEED THE GRAVITY TO KEEP AN ATMOSPHERE ON THE PLANET, AS WELL.

JADEN: HI, MY NAME IS JADEN, AND I GO TO OWYHEE ELEMENTARY SCHOOL.

MY QUESTION IS HOW DOES THE MOON CIRCLE AROUND THE EARTH?

DEVINE: SO THE MOON IS ACTUALLY BEING PULLED TOWARDS THE EARTH AT ALL TIMES.

AND SO ONE OF THE KIND OF CRAZY THINGS TO THINK ABOUT IS WHY, THEN, DOESN'T THE MOON GET PULLED BY EARTH'S GRAVITY AND JUST STRAIGHT INTO THE EARTH AND CRASH INTO THE EARTH?

SO ONE THING YOU CAN THINK ABOUT IS THAT THE MOON IS ACTUALLY NOT ONLY BEING PULLED TOWARDS THE EARTH, BUT IT HAS A SPEED AROUND THE EARTH, SO A VELOCITY.

SO IF EARTH WAS TO DISAPPEAR COMPLETELY, SO IF EARTH JUST VANISHED ONE DAY, THE MOON WOULD START TRAVELING IN A STRAIGHT LINE BECAUSE, REMEMBER, THINGS TRAVEL IN A STRAIGHT LINE UNLESS ACTED ON BY AN OUTSIDE FORCE, LIKE NEWTON'S FIRST LAW TELLS US.

SO WHAT'S HAPPENING IS YOU HAVE EARTH EXERTING A GRAVITATIONAL FORCE.

THE MOON WANTS TO TRAVEL IN A STRAIGHT LINE, BUT THE EARTH PULLS IT A LITTLE BIT, AND SO THE MOON CHANGES ITS DIRECTION.

AND THEN IT STARTS TRAVELING IN A DIFFERENT DIRECTION, AND EARTH PULLS IT AGAIN, AND IT CHANGES ITS DIRECTION.

SO ONE WAY YOU CAN THINK ABOUT IT IS THAT THE MOON IS ALWAYS FALLING TOWARDS EARTH, BUT IT'S JUST CHANGING ITS DIRECTION, SO INSTEAD OF FALLING TO THE SURFACE OF THE EARTH, IT JUST CONTINUES TO FALL AROUND EARTH IN A CIRCLE.

WILLIAM: HI, MY NAME IS WILLIAM.

I GO TO OWYHEE ELEMENTARY SCHOOL.

AND MY QUESTION IS HOW DOES A MAGNET WORK?

DEVINE: IT'S ACTUALLY A VERY DEEP QUESTION IN TERMS OF HOW A MAGNET WORKS.

THERE'S A LOT GOING ON IN HOW A MAGNET WORKS.

SO THE FORCE AT WORK THERE IS THE MAGNETIC FORCE.

BUT IT'S ALSO RELATED TO THE ELECTROSTATIC FORCE.

AND SO IF YOU WERE TO BREAK DOWN, IF YOU WERE TO LOOK AT THE VERY, VERY, VERY TINY PIECES THAT MAKE UP A MAGNET, SAY A BAR OF IRON THAT HAS A MAGNETIC -- HAS BEEN MAGNETIZED, WHAT YOU WOULD SEE IS THE INDIVIDUAL ATOMS THAT MAKE UP THE IRON IN YOUR MAGNET.

AND ALL OF THE ELECTRONS IN THOSE ATOMS ARE LINED UP SO THAT THEIR ORBITS ARE ALL ORIENTED THE SAME DIRECTION.

AND THAT'S KIND OF THE KEY OF HOW A MAGNET WORKS.

AND SO ALL OF THE ELECTRIC FIELDS OF THE ELECTRONS ARE IN THE SAME DIRECTION, AND ALL OF THOSE ELECTRONS ARE MOVING.

AND WHAT YOU MAY LEARN IF YOU TAKE A LOT MORE PHYSICS, SOMEDAY, IS THAT IF YOU HAVE A MOVING ELECTRICALLY-CHARGED OBJECT, LIKE AN ELECTRON, THAT GENERATES A MAGNETIC FIELD.

AND SO THE SHORT KIND OF QUICK ANSWER FOR HOW A MAGNET WORKS IS BECAUSE ALL THE ELECTRONS ARE ALIGNED, ALL THE FIELDS ARE ALIGNED, THEN THE MOVEMENT OF THOSE INDIVIDUAL ELECTRONS GENERATES THIS MAGNETIC FIELD, AND THAT'S WHY A MAGNET WORKS.

IF YOU HAD A PIECE OF IRON THAT DIDN'T HAVE ALL OF THE ATOMS ALIGNED, THEN IT WOULDN'T BE A MAGNET.

AND THAT'S WHY SOME PIECES OF IRON ARE MAGNETIC AND OTHERS AREN'T.

JENSON: HI, MY NAME IS JENSON.

I COME FROM OWYHEE-HARBOR ELEMENTARY SCHOOL.

MY QUESTION IS ARE ALL METALS AFFECTED BY MAGNETS?

GARDNER: THE ANSWER TO THAT IS NO, NOT ALL METALS ARE AFFECTED BY MAGNETS.

IT HAS TO DO SIMILAR TO WHAT KATIE JUST SAID ABOUT THE MAKEUP AND HOW THE ATOMS LINE UP IN THE INDIVIDUAL GRAINS OF THE METAL.

BUT WE CLASSIFY METALS AS FERROUS METALS, WHICH IS RELATED TO IRON CONTAINING METALS, AND NONFERROUS.

AND THAT'S THE CONNECTION OF WHETHER THEY'RE MAGNETIC OR NOT.

SO IT'S MOSTLY IRON THAT IS -- AND METALS THAT CONTAIN IRON THAT ARE ATTRACTED BY MAGNETS.

CARTAN-HANSEN: RONAN ASKS: CAN YOU HAVE A MAGNET GO SIDEWAYS?

GARDNER: I REALLY LIKE THIS QUESTION BECAUSE IT LETS US TALK ABOUT THE NATURE OF FORCES, AS WELL.

SO FORCES ACT ALONG THE LINE.

AND SO IF TWO MAGNETS CAN EITHER ATTRACT EACH OTHER OR PUSH EACH OTHER APART, DEPENDING ON HOW THE NORTH AND SOUTH POLES ARE ARRANGED, BECAUSE MAGNETS HAVE NORTH AND SOUTH POLES.

AND SO OPPOSITES ATTRACT, AND LIKE POLES PUSH AWAY FROM EACH OTHER.

AND SO, YEAH, YOU COULD MAKE A MAGNET GO OFF IN A DIRECTION OTHER THAN THAT STRAIGHT LINE.

AND THAT'S IF THE MAGNET IS SITTING ON LIKE, SAY, A TABLETOP AND YOU PUSH A MAGNET DOWN ON TOP OF THE TABLE FROM THERE, IF THE POLES ARE DIFFERENT, IT WILL JUMP UP AND HIT THAT MAGNET.

BUT IF THEY'RE DIFFERENT, THAT MAGNET'S PUSHING AND TRYING TO GET THROUGH THE TABLE, BUT IT CAN'T.

AND SO EVENTUALLY IT WILL GET A LITTLE BIT OFF CENTER, AND IT WILL SCOOT OFF TO THE SIDE.

AND SO THAT'S THE WAY THAT THE MAGNETS CAN MAKE A FORCE THAT'S NOT IN THE SAME DIRECTION AS THE LINE BETWEEN THEM.

COLTON: HI, MY NAME IS COLTON.

I GO TO SAGLE ELEMENTARY SCHOOL.

AND MY QUESTION IS WHY DOES THE FORCE CHANGE THE SPEED OF AN OBJECT?

DEVINE: WELL, YOU CAN THINK OF THAT THROUGH YOUR EXPERIENCE.

AND I THINK THAT'S PROBABLY HOW NEWTON CAME UP WITH THE SECOND LAW THAT A FORCE DOES CHANGE THE SPEED OF AN OBJECT.

IF YOU PUSH ON SOMETHING, IT WILL MOVE.

AND SO THAT'S REALLY THE HEART AND SOUL OF NEWTON'S SECOND LAW.

IF YOU GIVE SOMETHING A PUSH, YOU'RE GIVING IT ENERGY; THAT CHANGES THE SPEED OF THE OBJECT.

AND SO YOU CAN TIE THIS BACK, THEN, TO MAYBE CONCEPTS OF ENERGY.

WHEN YOU'RE PUTTING A FORCE ON AN OBJECT, YOU'RE ALSO SPEEDING IT UP OR SLOWING IT DOWN AND CHANGING THE AMOUNT OF ENERGY.

SO YOU'RE TRANSFERRING SOME ENERGY FROM YOU TO THE OBJECT.

(MUSIC) CARTAN-HANSEN: GRAVITY HOLDS OUR WORLD TOGETHER.

IT EVEN HOLDS THE AIR IN OUR ATMOSPHERE.

BUT WHAT IS GRAVITY?

GRAVITY IS THE FORCE OF ACTION BETWEEN TWO OBJECTS.

IN THIS CASE BETWEEN THE MELONS AND THE EARTH.

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.

YOUR BODY HAS MASS AND SO DOES YOUR FRIEND'S.

SO THERE'S A GRAVITATIONAL PULL BETWEEN THEM.

OH, NO, THAT DOESN'T HAPPEN.

YOUR BODIES DON'T HAVE ENOUGH MASS TO BE PULLED TOGETHER LIKE THAT.

STUDENTS: WHEW.

CARTAN-HANSEN: BUT THE EARTH'S GRAVITATIONAL PULL IS STRONG BECAUSE IT HAS 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 EFFECT 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 EARTH BECAUSE THE POWER OF THE ROCKET IS USED TO PUSH THE SPACE SHUTTLE OUT OF EARTH'S ATMOSPHERE.

BUT SPACE SHUTTLE ASTRONAUTS NEVER TRAVEL BEYOND EARTH'S GRAVITATIONAL PULL, THEY JUST KEEP MOVING FAST ENOUGH TO KEEP GRAVITY FROM PULLING THEM BACK TO EARTH.

IT'S CALLED A STATE OF WEIGHTLESSNESS OR, AS NASA CALLS IT, "MICROGRAVITY."

THESE BOISE STATE UNIVERSITY ENGINEERING STUDENTS ARE FLYING IN A SPECIAL AIRPLANE THAT CAN CREATE MOMENTS OF WEIGHTLESSNESS.

(WHOOPING) THEY'RE STUDYING THE EFFECTS OF MICROGRAVITY 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.

STUDENT: "BEST FEELING IN THE WORLD" CARTAN-HANSEN: SO GRAVITY IS ONE OF THE FUNDAMENTAL FORCES IN NATURE.

WE REALLY DON'T KNOW WHAT CAUSES GRAVITY, BUT WE SURE FEEL THE EFFECTS OF GRAVITY.

WHOA, YOU OKAY?

STUDENT: YEAH.

WHAT GOES UP MUST COME DOWN.

IT'S JUST GRAVITY.

(MUSIC) LILIANA: HI, MY NAME IS LILIANA.

AND I GO TO OWYHEE-HARBOR ELEMENTARY SCHOOL.

AND MY QUESTION IS HOW DO AIRPLANES FLY WHEN GRAVITY IS PULLING THE AIRPLANES DOWN?

GARDNER: WHAT A TERRIFIC QUESTION.

AND I THINK IT WOULD BE VERY -- IT WOULD BE HARD NOT TO ASK THAT QUESTION WHEN YOU SEE AIRPLANES BECAUSE THEY'RE REALLY HEAVY OBJECTS, AND THEY HAVE A LOT OF GRAVITY ACTING ON THEM.

AND THE ANSWER TO THAT QUESTION HAS TO DO WITH THE SHAPE OF THE WINGS.

IT'S CALLED THE "AERODYNAMIC FORCE."

AND THE ENGINES OF AN AIRPLANE PUSH IT THROUGH THE AIR AT A VERY HIGH SPEED.

AND AS THE AIR RUSHES AROUND THE SHAPE OF THE WINGS, THE NET EFFECT IS THAT IT HAS A FORCE THAT PUSHES UPWARD ON THE WINGS AND THAT LIFTS THE PLANE INTO THE AIR.

SO IF A PLANE WERE TO STOP, IF IT DIDN'T HAVE THAT FORWARD VELOCITY, IT FALLS RIGHT AWAY.

SO IT HAS TO GO FAST TO FLY, AND THAT'S WHY PLANES GO FAST.

MILLIE: HI, MY NAME IS MILLIE, AND I GO TO BASIN ELEMENTARY SCHOOL.

THE QUESTION I WOULD LIKE TO ASK IS WHAT WOULD HAPPEN TO US IF WE HAD NO GRAVITY AT ALL.

GARDNER: THAT'S THE KIND OF QUESTION THAT PEOPLE WHO ARE REALLY INTERESTED IN SCIENCE FICTION MIGHT ASK.

AND I LOVE THE QUESTION BECAUSE THE ANSWER IS WE COULDN'T EXIST.

THE PLANET WOULDN'T HAVE FORMED IN THE FIRST PLACE.

WE'D HAVE NO ATMOSPHERE ON THE PLANET.

WE WOULDN'T BE ABLE TO WALK ON THE PLANET.

GRAVITY REALLY IS WHAT ALLOWS EXISTENCE, AS WE UNDERSTAND IT, TO HAPPEN.

IF IT WEREN'T FOR GRAVITY, THERE MIGHT BE LIFE, BUT IT WOULD BE VERY HARD TO IMAGINE WHAT IT WOULD LOOK LIKE.

DEVINE: ANOTHER KIND OF FUN THING TO THINK ABOUT IS, LET'S SAY THAT WE HAD HAD GRAVITY SO WE COULD FORM, BUT THEN SUDDENLY SOMEBODY TURNED OFF GRAVITY, AND IT ALL WENT AWAY.

AT FIRST YOU PROBABLY WOULDN'T NOTICE IT RIGHT AWAY UNTIL YOU EXERTED A FORCE THAT WOULD PUSH YOU OPPOSITE GRAVITY.

SO YOU MIGHT BE SITTING IN YOUR CHAIR, YOU WOULDN'T NOTICE, AND THEN YOU'D STAND UP, AND SUDDENLY YOU'VE EXERTED A FORCE PUSHING AWAY FROM EARTH, AND THERE'S NOTHING TO BRING YOU BACK UP, AND YOU'D GO FLOATING AWAY FROM THE SURFACE OF EARTH.

THE OTHER THING THAT I THINK WOULD BE VERY BAD, THAT WE'D NOTICE RIGHT AWAY, IS THAT OUR ATMOSPHERE WOULDN'T BE GRAVITATIONALLY BOUND TO EARTH ANYMORE.

SO EVENTUALLY, PRETTY QUICKLY, PROBABLY, OUR ATMOSPHERE WOULD EVAPORATE AWAY FROM THE SURFACE OF THE EARTH AND WE WOULDN'T HAVE ANY AIR TO BREATHE.

AND SO WE DON'T WANT GRAVITY TO GO AWAY.

GRAVITY HELPS US, KIND OF, STAY ALIVE AND STAY ON THE SURFACE OF THE EARTH WHERE WE BELONG.

CARTAN-HANSEN: CONN ASKS: HOW DOES FRICTION WORK?

DEVINE: FRICTION IS A FORCE THAT'S A CONTACT FORCE BETWEEN TWO SURFACES.

AND SO IF YOU HAVE LIKE YOUR HAND AND YOUR OTHER HAND AND YOU RUB THEM TOGETHER, YOU'RE CREATING A FRICTIONAL FORCE.

AND THAT FRICTIONAL FORCE IS WHAT MAKES YOUR HANDS WARM UP WHEN YOU RUB THEM TOGETHER.

AND SO THE WAY THAT FRICTION WORKS, THEN, IS YOU JUST NEED TO HAVE THE SURFACE OF ONE OBJECT IN CONTACT WITH THE SURFACE OF THE ANOTHER OBJECT.

AND THE RUBBING TOGETHER OF THOSE TWO SURFACES CREATES FRICTION.

HALLIE: HI, MY NAME'S HALLIE, AND I GO TO ROCKY MOUNTAIN HIGH SCHOOL.

AND I WAS WONDERING WHAT THE DIFFERENCE BETWEEN CENTRIFUGAL FORCE AND CENTRIPETAL FORCE WAS?

DEVINE: THAT'S A GREAT QUESTION.

AND A LOT OF PEOPLE GET CONFUSED BY IT, A LOT OF ENGINEERING STUDENTS IN MY CLASSES GET CONFUSED BY THAT.

BUT THEY'RE TWO WORDS THAT REFER TO THE SAME EFFECT BUT HAVE SUBTLY DIFFERENT MEANINGS.

SO THE BEST WAY TO ANSWER THAT IS TO IMAGINE A SITUATION WHERE YOU HAVE A BALL AND A STRING, AND YOU'RE SWINGING IT AROUND OVER YOUR HEAD.

SO THE STRING CONSTRAINS THE BALL TO GO IN A CIRCLE.

AND IT'S CONSTANTLY ACCELERATING BECAUSE THE VELOCITY IS CONSTANTLY CHANGING DIRECTION.

AND TO CAUSE THAT ACCELERATION, TO CAUSE THAT CHANGE IN VELOCITY, THE STRING DOES THAT BY EXERTING A FORCE, THE TENSION IN THE STRING; THAT'S THE CENTRIPETAL FORCE THAT KEEPS THE BALL GOING IN A CIRCULAR DIRECTION.

CENTRIFUGAL FORCE ISN'T REALLY A FORCE.

IT'S THE TERM WE USE TO DESCRIBE THE EFFECT OR THE TENDENCY OF THE BALL TO MOVE OUT OF THE CIRCLE.

IT'S THE CENTRIPETAL FORCE THAT COUNTERACTS THAT AND MAKES IT GO IN THE CIRCLE.

DEVINE: SO THE THING I ALWAYS TELL MY STUDENTS TO REMEMBER, TOO, IS THAT IN CIRCULAR MOTION WHEN BOTH OF THESE FORCES ARE AT PLAY HERE, WHEN WE TALK ABOUT BOTH OF THESE FORCES, IN CIRCULAR MOTION, CENTRIPETAL MEANS CENTER-SEEKING.

AND SO CENTRIPETAL FORCES ARE REAL FORCES, LIKE TENSION FROM A STRING, BUT ALSO GRAVITY.

SO EARTH PULLING ON THE MOON.

THE MOON IS ORBITING BECAUSE OF A CENTRIPETAL FORCE.

AND CENTRIPETAL FORCES YOU CAN ALWAYS POINT TO SOMETHING AND SAY, GRAVITY, THAT'S A CENTRIPETAL FORCE, OR TENSION, THAT'S A CENTRIPETAL FORCE.

CENTRIFUGAL FORCES ARE THIS KIND OF, LIKE JOHN SAID, IMAGINARY FORCES, THIS BIG FORCE THAT'S MORE OF OUR PERCEPTION.

AND SO IF YOU'VE EVER HEARD OF THOSE FAIR RIDES, THE GRAVITRON, WHERE YOU GO IN AND THE ROOM, ITSELF, SPINS IN A CIRCLE AND YOU FEEL YOURSELF SUCKED OUT TO THE WALL, WELL, YOU'RE PERCEIVING; YOU DON'T KNOW FROM BEING INSIDE THE ROOM THAT THE ROOM IS ROTATING.

AND SO IT FEELS LIKE, TO YOU, LIKE YOU'RE BEING PULLED BY A FORCE.

AND THAT KIND OF IMAGINARY FORCE THAT'S NOT ACTUALLY GRAVITY OR TENSION OR ANYTHING, BUT IT'S HAPPENING BECAUSE THE ROOM IS ACTUALLY SPINNING, YOU JUST DON'T KNOW IT; THAT'S A CENTRIFUGAL FORCE.

CARTAN-HANSEN: MIA ASKS: HOW CAN YOU MAKE YOURSELF GO DOWN A SLIDE FASTER?

DEVINE: SO NO MATTER WHAT, GRAVITY IS GOING TO EXERT THE SAME AMOUNT OF FORCE ON YOU.

AND SO YOU'RE A SET AMOUNT OF MASS, THE EARTH IS A SET AMOUNT OF MASS, AND EARTH IS GOING TO PULL YOU DOWN.

SO THE THING THAT SLOWS YOU DOWN ON A SLIDE, THEN, IS THE FRICTION BETWEEN YOUR BODY AND THE SLIDE.

AND SO TO GET THE BEST AMOUNT OF SPEED, WHAT YOU WANT TO DO IS REDUCE THE AMOUNT OF FRICTION BETWEEN YOU AND THE SLIDE.

AND SO YOU'D WANT TO DO THINGS LIKE REDUCE THE AMOUNT OF SURFACE AND CONTACT WITH THE SLIDE OR WEAR PANTS THAT ARE REALLY SLIPPERY.

SO SLIPPERY CLOTHING IS PROBABLY THE BEST WAY.

BUT THE KEY IS TO MINIMIZE THE FRICTION BETWEEN YOUR BODY AND THE SLIDE.

CARTAN-HANSEN: KATHRYN, WHY DID YOU WANT TO STUDY PHYSICS?

DEVINE: WELL, ORIGINALLY, I DIDN'T WANT TO STUDY PHYSICS BECAUSE I DIDN'T REALLY KNOW WHAT PHYSICS WAS GOING TO BE ALL ABOUT.

SO WHEN I STARTED IN COLLEGE I THOUGHT I WANT TO BE, ACTUALLY, A BIOLOGIST AND STUDY BIOLOGY.

AND I WAS FASCINATED BY BIOLOGY.

AND THEN I TOOK A GEOLOGY CLASS, AND I WAS FASCINATED BY GEOLOGY.

AND THEN I TOOK A CHEMISTRY CLASS, AND I THOUGHT CHEMISTRY WAS GREAT, TOO.

SO I REALLY DIDN'T KNOW WHAT I WANTED TO DO, BUT I DIDN'T THINK IT WAS PHYSICS.

AND SO I TOOK PHYSICS BECAUSE IT WAS REQUIRED FOR ALL OF THE OTHER FIELDS.

YOU HAD TO TAKE PHYSICS IN ORDER TO BE A GEOLOGIST OR A BIOLOGIST OR A CHEMIST.

AND IN THAT PHYSICS CLASS I REALIZED THAT PHYSICS WAS REALLY THE STUDY OF, ON THE VERY FUNDAMENTAL LEVEL, WHY DO THINGS WORK.

AND SO PHYSICS HELPED EXPLAIN BIOLOGY, PHYSICS HELPED EXPLAIN GEOLOGY, PHYSICS HELPED EXPLAIN CHEMISTRY.

AND SO I REALIZED THAT THIS WAS THE SCIENCE THAT KIND OF TIED EVERYTHING TOGETHER, AND THIS WAS THE PLACE FOR ME.

CARTAN-HANSEN: JOHN, IF SOMEONE IS INTERESTED IN BECOMING A PHYSICIST OR AN ENGINEER, WHAT SHOULD HER OR SHE STUDY IN SCHOOL?

GARDNER: SO WHEN YOU'RE IN GRADE SCHOOL, OBVIOUSLY, YOU DON'T HAVE A LOT OF CHOICES.

YOU SHOULD JUST STUDY HARD, ALL THE TIME.

PAY ATTENTION IN CLASS AND DO YOUR WORK.

AND PROBABLY THE MOST IMPORTANT CLASS TO BE PAYING ATTENTION TO THAT RELATES TO THOSE IS YOUR MATHEMATICS CLASSES.

AND I THINK IT'S IMPORTANT TO REALIZE THAT TO BE A PHYSICIST OR ENGINEER YOU DON'T NECESSARILY HAVE TO LOVE MATH, BUT YOU HAVE TO BE PRETTY GOOD AT IT, AND YOU HAVE TO BE ABLE TO MOVE ON TO THE NEXT CLASS.

AS YOU GET INTO HIGH SCHOOL, TAKE A CHANCE TO TAKE YOUR PHYSICS CLASS OR CHEMISTRY.

AND FROM THE ENGINEERING STANDPOINT, DON'T FORGET THAT MAYBE THE MORE PRACTICAL CLASSES, LIKE A SHOP CLASS OR, YOU KNOW, SOMETHING IN -- WORKING WITH YOUR HANDS, THAT CAN BE VERY USEFUL, TOO.

IT DOESN'T HELP WITH THE THEORETICAL BACKGROUND, BUT IT HELPS YOU UNDERSTAND MACHINES AND HOW THEY WORK, AND THAT'S A REALLY IMPORTANT UNDERSTANDING TO HAVE WHEN YOU GO INTO ENGINEERING.

CARTAN-HANSEN: I'M SORRY, WE'VE RUN OUT OF TIME.

MY THANKS TO KATHRYN AND JOHN FOR ANSWERING STUDENTS QUESTIONS.

DEVINE: THANKS.

THIS WAS A LOT OF FUN.

GARDNER: AND WE'RE GLAD TO BE HERE.

CARTAN-HANSEN: MY THANKS ALSO TO THE FOLKS HERE AT THE DISCOVERY CENTER OF IDAHO FOR HOSTING US.

NOW, YOU CAN LEARN MORE ABOUT FORCE AND MOTION AND LOTS OF OTHER SCIENTIFIC TOPICS ON THE SCIENCE TREK WEBSITE.

WE'LL ANSWER MORE QUESTIONS ABOUT FORCE AND MOTION ON SCIENCE TREK: THE WEB SHOW .

AND IF YOU WANT TO SUBMIT A QUESTION FOR SCIENCE TREK , IT'S EASY.

AND YOU AND YOUR CLASS CAN WIN PRIZES.

YOU CAN SEND IT AS AN EMAIL OR AS A VIDEO QUESTION, RECORD IT ON YOUR WEBCAM OR CELL PHONE.

AND IF YOU'RE AN EDUCATOR, WE'LL EVEN LEND YOU A CAMERA.

OUR LAST PRIZE WINNER WAS CARLEY IN MRS. SHANE'S CLASS AT SAGLE ELEMENTARY IN SAGLE, IDAHO.

SO TO FIND OUT ALL ABOUT FORCE AND MOTION, HOW TO SEND IN YOUR QUESTIONS, AND HOW TO WIN, GO TO THE SCIENCE TREK WEBSITE.

AND EACH WEEK CHECK OUT MY BLOG FOR THE LATEST SCIENCE NEWS FOR KIDS.

YOU'LL FIND IT ALL AT IDAHOPTV.ORG/SCIENCETREK.

THANKS FOR JOINING US.

WE'LL SEE YOU NEXT TIME ON SCIENCE TREK .

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CARTAN-HANSEN: IF YOU WANT TO LEARN MORE ABOUT THIS TOPIC OR WATCH OUR VIDEOS, CHECK OUT THE SCIENCE TREK WEBSITE AT IDAHOPTV.ORG/SCIENCETREK.