IDTIMWYTIM: Centrifugal Force
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- Опубліковано 4 чер 2012
- In this edition of IDTIMWYTIM, Hank addresses the so-called centrifugal force, and explains why you really mean centripetal force.
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References for this episode:
www.lhup.edu/~dsimanek/glossar...
phun.physics.virginia.edu/topi...
www.newton.dep.anl.gov/askasci...
Wait, was that... outside? Such a mythical land.
KainPyrotic What is this "outside" you speak of.
This comment aged poorly
I dunno, I think last year it was more relevant to more people than ever.
7 YEARS AGO!!??
10 years ago?!?
While I was wasting time quoting, you got around the no-url filter. Brilliant!
need more episodes outside of the studioooooo!!!!!!!!!!
you are my life saver SciShow!! I need this for my test tomorrow
I have taken years of high school and collegiate physics and all my instructors have failed to explain this as well as you have.
Tyler Morrison alright, can I have a try?
I think it is easier to understand centrifugal force, if you first look at a different situation and then transfer your insights back to the original problem (don't worry, if you don't see what I mean by that, it'll work out)
so, imagine you're driving a car and you're approaching a red light. hopefully, you will slow down your car. what does your body feel when the car slows down? yes, it feels a "forwards force", although actually the car is decelerating, hence experiencing a "backwards force".
why do you feel that forwards force? because of inertia. when you apply the brakes the car decelerates, because the brakes apply a backwards force on the car (Newton II). your body however, remains it's speed, because there is no force applied to it (Newton I, inertia). so, relative to the car, your body accelerates, hence experiencing this forward force.
now, it's exactly the same principle with circular motion, only this time the car is the ball, the string is the brakes applying not the backwards force but the centripetal force, and that funny forwards force from before is now the centrifugal force.
to be honest, I have no idea, why centrifugal force and centripetal force have the same magnitude, and the exact opposite direction, but it should be clear now, why there's such a thing as centrifugal force
That's one of the worse explanations I've ever heard about this topic. How you can talk about centrifugal force without mentioning galilean and non galilean frames of reference is beyond me.
"As with most things in theoretical physics, Isaac Newton said it first." Love it!
YAY! I asked Vertasium to do a video on this misconception...i didn't see this before. Thank you Derek. Thank you Hank for taking care of my biggest pet-peeve in physics!!!!
I loved this video. Thank you for explaining this in an easy to understand fashion.
Now I wanna play some Tether-ball.
I'm struggling with physics, but these videos give me a comfort. They're so much more digestible. Thank you!
I'm really glad Hank explained this to us, although I'm not sure how I didn't see it until over five years after it came out. . . I learned about centrifugal and centripetal forces on populations (which are exactly what you'd think they are, considering what we think centrifugal and centripetal forces are in science) in my AP Human Geo class and was wondering if there were similar things in science.
I just explained this to my friend a couple days ago! I feel like such a knowledgeable high schooler now :)
1:43 -- Pulling it toward the ball, or pulling it toward the pole?
+lucromel
To calculate centripetal force: (m x v^2) / r
To calculate centrifugal force: -(m x v^2) / r
Therefore they are equal and opposite.
But they are not an action / reaction pair. The action - reaction pair, here, is : 1) the pole pulls on the ball via the string
2) the ball pulls on the pole via the string.
There are other pairs. For instance, we can suspect that the pole is implanted in the ground, and when the ball pulls on the pole, the ground pushes on the pole in the other direction, ensuring that the pole remains in place.
1st clear & easy explination I've found. Thank you Sir.
I'm a tutor at a university, and I'm always explaining this to my tutees, but they never believe me... Thank you, Hank - I appreciate this video.
Need to an IDTIMWYTIM on Gravity. A lot of people have no clue what it means...
As well as The Speed of Light :D
They would do it, if scientists actually knew what gravity is
has anyone else noticed that the letters of the acronym IDTIMWYTIM is incorrect. Hank is saying i dont think "that" means what you think it means. either the second I needs changed to a T or Hank needs to say i dont think "it" means what you think it means.
My favorite sci show yet :)
Got a physics exam on this stuff in a few days. Super concise and clear explanation! :D
A comic on Centrifugal Force: xkcd.com/123/
You spin me right round, baby, right round, in a manner depriving me of an inertial reference frame, baby.
Wasn't inertia first described by Galileo, if in a less elegant way?
Yes, The Law of Inertia was suggested by Galileo, actually Newton just used the existing concept to describe motion.
The idea of inertia came way before Newton and Galileo. Look up Mozi's Mo Ching, who first realized that an object's default is straight line constant motion.
@@carultch
Maybe, but did Galileo know about that or was it something he discovered independently?
.
Newton certainly knew about Galileo.
@@IamGrimalkin Galileo certainly lived in a time when he could've learned about the Mo Ching. He lived in the home country of Marco Polo, several centuries after trade with China became an established practice.
I certainly cannot speak for whether Galileo did or didn't know about this in advance, or whether he discovered the law of inertia independently. Agreed that Newton stood on the shoulders of Galileo, since Galileo laid the groundwork for a lot of Newton's work.
These bios are edited really well!
Thanks man. I had several years of college level physics, dynamics, etc. And I don't think this was ever explained to me so clearly
Is this what happens to space craft in orbit? Only the string is gravity?
Yes! That's exactly what happens. I'ts been explained to me before but poorly and only now with that analogy I've caught on to what they were saying. So the astronauts never experience "Zero Gravity", they aren't absent from gravity they're just constantly in free-fall and never allowed to go down toward earth.
Ethan Latsinos They have enough outward momentum to balance with the effects of gravity, the only net force is in a circular path around the Earth.
@@ArchAngelSlayer1 The net force on a spacecraft in orbit acts radially inward toward Earth. And is equal to the force of gravity acting on the spacecraft. There is no net force that is "in a circular path around Earth", unless they turn on the rocket engines and propel themselves tangential to the path.
The reason astronauts feel weightless in a spacecraft, is that you cannot actually feel gravity. You only feel the constraint forces, that you instinctively assume are acting on you because of gravity. Since gravity acts uniformly on every kilogram of the spacecraft and its occupants, and causes the same inward acceleration of every mass on board the spacecraft, there end up being no constraint forces that hold the occupants at rest. The weight is nullified by the fact that the astronauts are accelerating along with gravity, and therefore feel weightless.
If you stood on a ladder fixed to Earth that extended as high as the international space station, you would weigh about 95% of your ordinary weight on the ground. That's how much the true gravity is, on astronauts in orbit.
This is a good video. But a warning to would-be pedants out there.
From my Classical Mechanics textbook (upper-level physics major text) by John R. Taylor:
"In most introductory physics courses, the centrifugal force is dismissed as an abomination to be avoided by all right-thinking physicists. As long as we confine our attention to inertial frames, this is a correct (and certainly a safe) point of view. Nevertheless... from the point of view of a noninertial rotating frame there is a perfectly real centrifugal force mω^2ρ (perhaps more familiar as mv^2/ρ)"
Basically, it is perfectly acceptable (and honestly more correct) to use centrifugal force as a term to describe what's happening in certain situations. The thing that makes you lighter at the equator than the poles is definitely centrifugal force.
Just, make everyone's day a little less annoying and don't correct people if the extent of your knowledge comes from an online video.
"Just, make everyone's day a little less annoying and don't correct people if the extent of your knowledge comes from an online video."
If only the average person that watched these sort of videos followed that.
This is from my University Physics with Modern Physics text (13th edition by Freedman & Young) :
"In an inertial frame of reference there is no such thing as “centrifugal force.” We won’t mention this term again, and we strongly advise you to avoid using it as well."
The text literally never mentions the term again. Though, it must be noted that it does qualify the statement, maintaining that it does not exist _in an inertial reference frame_, which at least implies that it _IS_ valid in rotating frames, but doesn't specifically endorse it's use in such situations like your text does. I guess this is the type of 'introductory physics courses' your text was referring to.
It doesn't make sense to me why some textbooks endorse the use of centrifugal force (in the proper context), and others almost seemingly equate it to the devil. Even if the textbooks are geared toward introductory courses, the _AUTHORS_ of such textbooks would have certainly taken advanced courses that endorse its use. Got any explanation for this? I sure don't.
Willoughby Krenzteinburg Young and Freedman has got to be the worst textbook I've ever bought, I'm still annoyed that my university suggested me that in first year years ago. I'd take everything in it with a massive grain of salt (though, there really isn't much in it to take with salt anyway)
I used Young and Freeman in my Freshman physics course. The reason they strongly advise you *not* to use the term is because in freshman-level mechanics you will *never* be doing physics on non-inertial frames of reference.
The reason why advanced textbooks say this is wrong is because the physics there is an *actual* centrifugal term from a rotating frame of reference. Newton's Second Law in a rotating frame is:
ma = F + 2mv x Ω + m(Ω x r) x Ω
Ω = angular velocity, a vector
a,v,r are vectors and the x is the cross product
The Coriolis Force, Fc is
Fc = 2mv x Ω
The Centrifugal Force, Fcf is
Fcf = m(Ω x r) x Ω
So Fc and Fcf don't appear in inertial frames of reference. But they're super real if you're in a non-inertial one.
Earth is regarded as "roughly inertial." When you throw a baseball, Fc and Fcf affect the destination of your baseball much less than drag (which you should also be thankful freshman courses ignore). Fire an ICBM, and suddenly those terms are super important, and very real.
(I know this was probably way more than anyone wanted)
Willoughby Krenzteinburg Because Taylor has an entire chapter dedicated to nonintertial frames, meaning that ignoring fictitious forces like the centrifugal force would be really really stupid. According to wikipedia, Young doesn't, so it doesn't need to bother with it.
this was a very clear and concise explanation, thank you
i really thank you for giving people a look at science that is appealing and informative. thank you hank really thank you
Centrifugal force is just one of those things that we should just accept and use in common needs. It feels like it's moving away, that's enough reason. You make tests as a kid and what do you discover naturally? It tries to move away from you, you let go, it goes. That's about as far as we need to define the whole thing in order to explain perfectly well what is happening to another humanbeing.
When you really need to calculate something, then it becomes important to use correct terms, but if you're calculating centripetal forces, odds are you didn't just thought of it in your own head, you were taught how to do it.
Only thing that really changes, is the direction of the force, which is counter-intuitive, harder to understand. I certainly will use centrifugal, instead of explaining everytime like a nosy kid that "no, it's centripetal because...." and everyone in the room instantly hates me. I would too.
Of course, the ideal would be to have more people who understand basic concepts and theories.. "But that's a sin" says the congressman...
But... it was just explained why centrifugal force as we 'know' it... is wrong. Why would you want to perpetuate something that's wrong? Why not teach it to people? O.o Just because something 'feels' like it's moving away doesn't mean that what you're feeling is scientifically correct. You could use that argument for anything fictitious if that's the case.
Just call it the Centrifugal Effect :P
^^ That's quite good, actually, i like it.
@TheRubberWolf: Because that's how you understand the phenomenon if no one is there to tell you otherwise.
There are things that need to be scientifically correct and things that are easy to understand. When you swing that ball in a string, you don't feel the force moving towards you. Only when you need to make calculations, the actual direction is important. In fact, i'm pretty sure that since only the sign changes, even calculations aren't that hard..
Same goes for a lot of basic stuff. You don't need to know that cold is not a thing but an absence of heat. If everything was explained like it is, we wouldn't have many scientists.. Some concepts are just illogical when it comes to everyday life.
If we started talking in perfect scientific terms, language would become very strange indeed. Not to mention, complicated, inefficient..
@Switzer The more i think about Centrifugal Effect, the more i like it.. It really addresses the issue from both sides, making it easy to understand but still correct.
"So people can stop being so dumb". I am afraid you have failed, friend. Have you watched politics this year at all? Lol
This video was posted in 2012 bud
The production of dumb people will stop when humanity is extinct.
B4 Music And my comment was posted in 2016. Please do tell how my comment doesn't still make sense.
Same goes for this year
I love this show so much.
Thanks for the video. Really helped to differentiate Centripetal and Centrifugal Forces easily.
I don't believe this was properly explained.
Agreed! Hank should have read Newton's Philosophiæ Naturalis Principia Mathematica in the original Latin.
great vid man, helped me a lot :)
Great video, I think he did a really good job explaining it.
This is sooo great! We were just arguing about this in my physics class today!
About time. This deserves a like.
About that barrel ride: From your frame of reference in the ride it seems as if you are being pulled against the wall (centrifugal force). In actuality, your inertia is moving you in a straight line perpendicular to a line between you and the center of the barrel. The walls of the barrel are preventing you from continuing on that path and are exerting the force on you (like the string on the tether ball). This combined with the force due to friction between you and the wall keep you stuck.
Hey Hank,
First of all, great job on the CrashCourse Biology and the Sci-Show! I have a suggestion for your 'IDTIMWYTIM'-segment: The term 'queen' for the reproductive female within eusocial inscet colonies (bees, bumblebees, wasps, termite and especially ants) is often missused or missunderstood. Most people think of the queen as some sort of actual ruler and can't grasp the concept of collective intelligence....
This was my suggestion last time. :o SUCCESSSSSSSS! I feel special.
Hank: I think that it is time for the world to understand that when they are talking about "Internet Speed" as in 10Mbps (Mega bits per second) they are actually talking about bandwidth. Because electrons can only move so fast, so it's the amount you can pump through the cables.
As always, great show!! Keep it up, and we'll continue watching.
dude phenomenal explanation
More!! This is my favorite category!
I like all the history lessons, evolution, phsycological and other science videos, but you should definitely do more physics stuff. I think physics is the most interesting science
I haven't heard of this guy, I'll go check out his channel now, thanks!
Not picking on hank, but he threw the ball exactly the way I'd picture him throwing a ball. He also surprised me when he caught the ball, not that he could catch it, just his body language doing it. You're an enigma, hank green.
I don't really understand the co-ordinates because I'm not that old that I have learned stuff like that. But thank you for the long explanation, I appreciate people who put time into writing thorough comments that won't have the other person with more questions.
Finally someone who explains this concept effectively!,
Frantically panicking about centrifugal force two days before my A-level physics coursework is due in: Hank Green, you are a life-saver. This is brilliant.
@Scishow It really depends on what frame of reference you are using, in advanced physics courses, where rotating reference frames are used, the centrifugal force is "real" and does exist.
This, one of the simple ways to gauge the level of physics education people had is asking them about the centrifugal force.
Hank, what do you call the force that the rope exerts on the tetherball pole, making it sway around and around?
You explained this really well. Now I would love to just send everyone I know that doesn't understand this to your video, but that would require them all to understand English, which, sadly is not the case. So I guess in most cases I will have to do the explaining myself, which I can't do nearly as eloquent as you.
okay I have a video request idea can you please tell me why when you roll the window down in a car or truck on the other side you can feel vibrations in the air?
The process is theoretically mediated by gravitons, which are force-carrier particles. Each "real" force has a force-carrier particle that carries changes in characteristics (like mass or velocity) between other particles. Hank talks about it in the Sci Show videos for the weak and strong forces.
As he explained in the video, the force pulling you against the wall of a Gravitron is your own inertia which is trying to make you move in a straight line, at a tangent to the direction of spin.
Just came across your channel recently.
Have you done anything on quantum entanglement or Bell's theorem?
Every time I watch one of these particular segments, I think of the song Hank wrote called "I know." The one that only had ten words.
That, and The Princess Bride.
Is this in response to 1veritasium's video today? If not, you should really watch his stuff. It's great, and been in line with your posts a couple of times. PHYSICS!
So is the stability given to a bullet after the rifling of a bore makes it spin called centrifugal force or centripugal force?
Question: you said that Real Force requires physical interaction between objects. What if it would be possible to build a mechanism where a set of magnetic forces would act as the string does in the video? Would that still be considered a real force, or something else?
wow, that really clear things up for me
Could you explain why does the ball tends to go up and the rope straights up getting perpendicular to its base even if you didn't shoot the ball up and it doesn't "run" from the base?
You should do one on reaction forces, i.e. how the reaction isn't necessarily an object moving backwards but also the force it exerts on the thing pushing it.
Same thing. When the water is in the center of the bottle there is nothing keeping it from going forward (towards the edge of the bottle).At the edge of the bottle,the edge will exert a force perpendicular to the edge(normal force) which will keep the water in a circular motion. one thing to note is that the centripetal force is also a fictitious force that describes the need of a force to keep an object on a circular path. The force needs to be delivered by an actual force(tension in the video)
Scharfy, the force that holds you against walls on rides is centripetal force. Its just that instead of having a string hold you in place you have the walls or seat of the ride providing the force. The shape of the rollercoaster track and your velocity controls how much force is applied.
yes, its the same thing for the most part. I assume you mean something like a person spinning a ball in a cup attached to a string, right? in this case, the centripetal force on the cup is the force of tension that the string exerts on the cup. The centripetal force on the ball, however, is the normal (something like an upwards, resisting press) force exerted by the cup on the ball. I hope this kinda clarifies things.
I feel I must link you to the great Bad Astronomer and his wonderful explanation for why centrifugal force is totally a thing and why he and I both use the concept, sadly youtube does not seem to like the URL, but it can be seen on his Discovery Magazine blog under the topic 'When I say Centrifugal I mean Centrifugal'
My physics teacher described this even better:
When you're on a Merry-Go-Round and you're in the firetruck or police car or whatever, you may feel like you're being pushed outwards, against the side of said firetruck ect. Whereas actually, you just want to go in a straight line because of inertia. The side is there to stop you, it constantly pushes you to the middle, which feels to us like we're being pushed against it.
Thanks so much! I never understood this until now!
It works when considering the earth-sun system. Relativity teaches us that all reference frames are equivalent, bigger or not. Besides which it is usually possible for any reference frame to move 'outside' it.
Please do a video on 'Positivism'. I know it might be a bit more "theoretical" than others but misconceptions of positivism are abundant... (especially where it concerns metaphysical claims)... as I found out while writing my "philosophy of science" essay this semester.
Is this the reason that when you are in a vehicle and it turns left but yu lean right instead?
By perfect system, I was referring to an atmospheric system (I haven't gotten used to shortening things for UA-cam), since the weather will affect the ball and cord.
As for the other thing, it was poor wording on my part. The reason it seems to move to a ninety degree angle is the fact that it's anchored at all. The cord is stronger than the pull of the Earth's gravity on the ball, so it moves up. It's entire location change is because of the the combined effect of all the forces together.
It is a game involving 2 people in which the object is to wrap the ball all the way around the pole until the rope is wound tight, and the ball stops without bouncing. One player hits it clockwise from a top-down perspective, the other player hits it counter-clockwise from the same POV. There are numerous rules the players agree on before beginning play, resulting in various different game and play styles. It is somewhat similar to swingball, except played with a volleyball and without racquets.
ooooh now I get it. :D I've been wondering about this for a while!
Neat video!
Momentum. The force that you're feeling squishing you against the car is actually the force of the frame of the car (or the seat on the ride) pushing back against the direction of your momentum. Here's another example: imagine a car driving down a straight road until it comes to a 90 degree turn. In order to change it's trajectory, some force must be exerted on the car. In this case, that force will be friction between the wheels and the road. This frictional force is the centripetal force.
It depends on your definition of the dimensions, you can make colour dimensions or its Ph value, anything that can be measured is a dimension. In some circumstances spacial relations and time are useful as the first four dimensions, but that is not always the case.
so I don't think I've ever called the example centrifugal force as it was clearly being held in position. But then what force do you call that ride which forces me against the wall so I can go upside-down etc... what controls it?
Yo hank I do Breakdance and when I spin on top of my head. I feel a force pulling me outwards and not inwards can you explain this ? I don't feel the centripetal force ... why is that ?
I only ever referred to Centrifugal force as the force that keeps water from spilling despite a cup being held horizontally while the cup is being moved at a speed faster than what allows the water to leave the cup. Do the sides and base of the cup then exert centripetal force on the liquid? Is that how that works?
as someone who loves physics, but doesn't have the time to do proper research, i love these videos.
Here's how I like to explain it: When you are in an accelerating car, it can feel like "some force" is pushing you back against the seat. But for most people it is easy to understand that in fact it is the seat pushing against you as you try to stay at the same speed. In the same way, when you take a turn in your car, it can feel as though "some force" is pushing you against the door, when in reality it is the door pushing against you as you try to keep going in a straight line.
The same thing, essentially. The water inside the bucket wants to keep on flying straight, but the bucket held by your arm is holding it in. The water acts as the ball does in Hank's example, and the bucket and your arm act like the string does in Hank's example, holding the water in. The water has inertia, the bucket and your arm has the centripetal force.
I wonder if you drew a line that followed the flight path of the tethered ball and then unravveled it into a straight line, how that would compare to the length of how far you could just throw the ball?
inconceivable!
i use centrifuges to separate matter by particulate size. large particulat accumulates in the bottom, or up the outermost side (caused by this force we are trying to name).
Please help??
@Jacefully I believe it is the differing densities that actually separate the substances but the machine may be called a centrifuge. This is why chemists weren't physicists. Or maybe they named the machine before it was determined that centrifugal force is a fictitious force. Hope this helps.
As for the space elevator, I think that has more to do with the properties of stuff orbiting in space. Like, if you put the center of mass of an elevator in a stable geostationary orbit (actually slightly above, for complicated reasons), the cable is 'hanging down' from orbit rather than the space station being 'held up' from the ground. There's tension pulling the cable up,, rather than pressure from gravity pushing it down.
Wikipedia has a decent diagram, search 'Space Elevator'.
Depends a little bit on your frame of reference. In relativity theory for example it is not a force but the bending of four dimensional spacetime. In particle physics it is one of the four fundamental forces and they are submitted via particles (similar to the electromagnetic force which is submitted by photons).
Seriously. Clear, concise, and completely shattering my world view.
Ah well, science is like that sometimes.
Haha, np. It's good practice explaining things :)
Essentially what I'm saying about a choice of co-ordinates is that it depends where you're looking from. If you're moving with the thing that's rotating (e.g. sitting on a roundabout) then you feel a real centrifugal force. If on the other hand you're standing next to a roundabout with a ball on it, you just see the ball moving in a straight line with no force acting on it.
So three questions came to mind...the first was the rotator ride which seems to have been answered satisfactorily. Second, we are assuming shot putters and discus throwers are taking advantage of centrifugal force when they do their spinny thing but they have a variety of techniques-is there an optimal way to throw? Third, which came first the centrifuge or the term centrifugal force?
I have a question. It isn't that I don't understand this video or that I disbelieve it, but if there isn't centrifugal force, what is it that, for example, pushes everyone riding on that one spinning ride at fairs (the Gravitron? I don't know, it doesn't matter, just an example) against the walls as it spins, away from the center?
Wait then what is it that keeps a ball in a cup when you spin the cup? is it the same thing?
Oh thank god!!!! That part of my brain that had me doing physics and maths all through school and then onto studying engineering at university is infinitely thankful to you for putting this out there!!
This conversation veered off in another direction. I was initially wondering why you claim the centrifugal force does exist. Still, you're right, and I never disagreed with you regarding Gallilean relativity or whatever this became.
beautiful explainer
Can you do an episode of IDTIMWYTIM about mutations?
yes thats correct, it is the term we use to describe the interactions between inertia and centripetal force however that is exactly the point
its an INTERACTION and NOT a FORCE