Physics: Centripetal vs Centrifugal Forces: Fiction in Physics

Hit play to learn about centripetal and centrifugal forces.

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Transcript

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go Well sometimes it feels like we're going in circles

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just going round and round not actually getting anywhere And

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here's a little secret Well it's true that's what we

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do in fact we're going in multiple circles all at

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once For one thing the earth is spinning on its

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axis and it's spinning really really fast like a thousand

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miles an hour kind of fast way faster than a

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racecar that's one circle But we're also orbiting the sun

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in a circle and that's even faster the earth and

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all of us on it air flying around the sun

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at around sixty seven thousand miles an hour to put

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that in scientific terms super crazy fast but actually that's

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a snail's pace when you look at our solar system

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is a hole because the sun the planets and everything

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else in our little neighborhood is whirling around the center

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Of our galaxy at a whopping five hundred thousand miles

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an hour Yikes And you thought you were just sitting

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in your chair not moving like a lump there So

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we've got circles within circles and yet we stay firmly

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attached to the ground How does that happen Why don't

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we go flying off into space like water flying off

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a dog when it shakes itself dry Well it's for

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the same reason that a tether ball doesn't go flying

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away from the pole it's tied to and the same

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reason this car is able to go around the track

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and that reason is centripetal force will centripetal force is

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the force that points toward the center of a circle

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when they're circular motion So when the moon orbits the

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earth well there's a centripetal force that keeps it from

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wandering on over to mars same with the race car

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and the tether ball But hold on how to the

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moon and tether ball in my car all have the

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same kind of force Well they don't A centripetal force

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isn't any specific type of force It could be a

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normal force or tension or gravity or some other kind

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Of force for that matter as any ancient roman khun

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tell you send trip it toe literally means center seeking

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in latin In the case of circular motion any force

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that acts toward the center of a circle is the

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centripetal force So centripetal is an adjective that describes how

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our forces acting rather than a type of force unto

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itself Now you may have heard of another kind of

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force It's the force you feel pushing you to the

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outside of a circle Like when you're chillin in the

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passenger seat When your mom realizes well she's about to

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miss her left turn you might feel a force smush

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ing your face against the window Well some people call

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that the centrifugal force and those people's pants are probably

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on fire because they're liars Okay well maybe it's a

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bit hard but the truth is that there's no such

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thing as sent terrific yl force It doesn't exist It's

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a myth a lie like mermaids or leper cons or

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fat free cheesecake that actually tastes good Now let's think

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back to what our old pal sir isaac newton said

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Newton's first law of motion says that objects in motion

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Tend to stay in motion and objects at rest and

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to stay at rest So when you're in the car

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trying to ignore your mom singing along every single eighties

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sung that ever existed well your body is moving in

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a straight line and your body has inertia that will

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keep moving in that straight line unless something acts on

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it So when she jerks the wheel to last well

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your body wants to maintain the motion in the pre

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turn direction Luckily there's seat belt and a door in

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a window that air preventing that in fact they're providing

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a centripetal force on your body and it's a good

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thing they are otherwise well you'd end up outside sidecar

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and that would hurt So while you feel like you're

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being pushed to the outside of the turn all your

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feeling is inertia Trying to keep you going in a

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straight line There's no extra force that suddenly pops into

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existence once something starts moving in a circle is just

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plain old inertia doing it's a you know inertia thing

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but wait If centripetal force points toward the center of

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a circle why doesn't the object just end up in

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The center of the circle Well we can find an

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explanation for this in outer space Not too far out

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Though The international space station is only about two hundred

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fifty miles away from earth We might think that astronauts

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in the space station float because there's no gravity up

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there but that's not true Two hundred fifty miles isn't

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close enough to escape earth's gravity In fact at that

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distance the force of gravity from our planet is on

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ly reduced by about ten percent But it sure doesn't

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look that way when we see those cool videos where

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everything is floating around The truth is that the space

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station and everything in it is falling Centripetal force in

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the form of gravity is pulling it toward the earth's

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core but it has velocity that's at a ninety degree

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angle to that centripetal force If we look at the

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circular orbit of the space station the velocity vector is

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always tangent to the circle Well a tangent to a

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circle is a line that only touches the circle at

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one point it's not going to cut through the circle

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at all and a line that's tangent to the circle

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Will always be perpendicular to the radius of the circle

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at the point where the tangent line touches creating that

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ninety degree angle So we have two vectors one first

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centripetal force and another for velocity Well when the planet's

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gravity pulls on the space station the space station feels

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that pole and falls down But the space station is

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moving perpendicular toe Whatever down is at any particular moment

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and it's moving really fast Like really really fast like

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five miles per second fast man does everything go faster

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than my race car anyway This velocity creates a situation

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where the space station isn't falling towards earth it's falling

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around the earth and because everything is falling at the

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same rate Well there's no way for anything Tohave Wait

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just think of tryingto weigh yourself on a scale while

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both u n the scale are in free fall It's

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a foolproof weight loss solution right up until you hit

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the ground Yeah so now we understand there's no such

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thing isn't terrific Yl force and the centripetal force describes

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a force that's pointed toward the center of circular motion

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Alright let's hop in the car and take a few

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Laps around the track here as we head into turn

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one what are the forces that are acting on the

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car and in what direction are these forces acting We're

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going to be getting the three dimensional treatment here but

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don't worry no special glasses will be required Let's ease

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into this question slowly we're always gonna have gravity to

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deal with right That's pointing straight down since we're not

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floating in the air we've also got a normal force

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from the pavement pushing us up And of course the

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engine in the car is providing a force that's making

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the car move forward then there's a force of friction

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that's acting in the opposite direction Well that's all well

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and good Nothing we haven't run into before by now

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we're like the picasso of free body diagrams but none

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of these forces air making the car turn let's look

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at a bird's eye view of the situation We won't

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worry about gravity in the normal force for right now

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we've got our applied force and friction right Well since

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we're turning left there has to be some centripetal force

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pointing to the left We could cheat and just label

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it f sub c for centripetal but that wouldn't be

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very accurate We should label this with a specific type

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of force so what's keeping the car from just maintaining

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its forward inertia well more friction the friction between the

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wheels and the tract pushes toward the center of this

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circular motion If you've ever made a sharp turn on

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a gravel road you know that the friction in that

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circumstance might not have been strong enough to keep you

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from sliding forward But thanks to our fancy high tech

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tires here i can make this turn at about one

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hundred seventy five miles an hour Sure it's not quite

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as fast as a space station but i'm doing pretty

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well here for standards and what would happen if we

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hit an oil patch and lost all our frictional force

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We keep on going straight in a line tangent to

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the curve were in because there's no such thing as

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a centrifugal force acting to maintain circular motion centripetal force

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is the tooth fairy of circular motion and sorry if

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you just found out the tooth fairy isn't really we're

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not going to get into the whole santa claus thing

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Here So we've seen a few examples of different centripetal

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forces Let's take a look at one more ever been

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to the carnival and ridden a grab a tron will

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a gravity tron is a ride that basically spins you

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around like you're inside of a top it might not

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sound that cool but it's been so fast that your

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inertia basically pins you to the wall and that lets

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you climb up the wall like you're floating your feet

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won't touch the floor in the ride we'll just be

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suspended above it Pretty cool right How is that possible

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Well after all it's not like gravity just goes away

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once you hand over your ticket and get in the

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machine What happens is that as the ride spins faster

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and faster the force of your inertia becomes stronger and

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stronger because your body wants to go straight it pushes

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hard into the walls of the ride The spinning khun

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get so fast that you can experience a force three

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times stronger than gravity because you're being pushed into the

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wall with so much force a force of inertia is

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greater than the force of gravity so inertia wins and

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you can lose contact with the ground without crashing down

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and you know hopefully the contents of your stomach don't

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come crashing up Okay so that makes sense But because

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we've got circular motion we know we need us in

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trip it'll force and it ain't gravity it's not friction

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either In the gravity tron the centripetal force that's pushing

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you toward the center of the circle is a normal

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force The normal force provided by the walls of the

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ride pushing back on you as your inertia pushes you

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against the wall centripetal force can be a little tricky

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Sometimes we really have to think about what's going on

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to determine what's creating the force So next time you

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feel like things are spinning out of control take a

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second to think about where all that spinning is coming

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from and hopefully you'll feel a centripetal force that keeps

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you from flying outside of the circle because well when

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that centripetal force let's go no other force that's not 00:10:50.488 --> [endTime] quite as nice