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Centrifugal Vs. Centripetal Force - A Better Explanation


Miles

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*Disclaimer: The purpose of this is to give an explanation that makes it easier to understand why centrifugal force is not a real force, as well as to make it easier to understand why centripetal force is a real force (and what centripetal force actually is).  Anyone who does not already know the difference should still be able to understand the basic differences from my explanation, as I aim to make this in layman's terms as much as possible.*


 

6c4886687b.jpg

 


 

First, what is the picture showing...

The large blue dot represents an object rotating in a circle around the center axis (the dot in the middle of the circle).  

The path that the object follows when rotating is the dotted line.

The arrows are color coded with their corresponding descriptions.

---

Next, let's define what the arrows' descriptions mean...

The blue arrow, velocity, is the speed of the object, and direction of momentum that the object wants to follow.

The red arrow, centripetal force, is the inward force that keeps the object going in a circle.

The green arrow, centrifugal force, is the outward force that is the tendency of an object to move away from the center axis.

---

Centrifugal vs. Centripetal Force

Centrifugal force is not real, but centripetal force is real.  

How is this so?

And now we get to reason why I posted this in the first place.  For a long time, I myself was very confused at the notion that centrifugal force is fake.  There were two reasons I didn't understand it.

One: The straight line that the two forces make seems to always to exist while the object keeps rotating in a circle.

Two: If the object were to break free of its circular motion, the object would follow the path that its velocity is carrying it.  So, to me, it seemed that because the aim of velocity is at a right angle to the line created by both the centrifugal and centripetal forces, that they both should have to be real.

What helped me realize what I was thinking wrong?

Well, I had to figure out if each of the forces was a pushing or a pulling force.  Is centrifugal force and outward push or pull?  Is centripetal force an inward push or pull?

And as soon as I asked myself those questions, I realized the answer through nothing other than the logic of semantics!  

Push: To exert force on [something] in order to move it away from oneself.
Pull: To exert force on [something] in order to move it toward oneself.

Centripetal force is an inward pull; Centrifugal force is an outward push.

Furthermore, it is necessary to remember which thing is acting as "oneself" in the definitions of push and pull when they are applied to diagram above.  By default, "oneself" must be the center axis, since the center axis = the pivot point, and all forces are defined in the pivot point's relation to the object in motion.

Now, the basis of that relies on Newton's Third Law.  If you aren't familiar with it, don't be worried about it being too hard to understand.  It's probably one of the most simple, fundamental laws that is easy to see.  Newton's Third Law states: For every action, there is always an equal and opposite reaction.  It is important to understand that by "action" he means exertion of force.

So, besides the obvious connection to this subject (that it explains why centripetal force is an inward pull and why centrifugal force is an outward push), that law actually provides the basis for using the center axis (pivot point) as "oneself" in the definitions of push and pull.  

So, how can we apply this to figuring out why centrifugal force is fake?

Cause and effect.

One of the forces must come first as the origin of its equal and opposite reaction.

To figure this out, let's use 2 real life examples.  

1. Imagine the object (the big blue dot in the picture) as a car driving around a left corner.  When you turn left, the car is being pulled left around the corner, and you are being pushed right because of your momentum, away from the pivot.

It is easy to see that the pull of turning left is the cause of being pushed right.  Therefore, pull comes before push.

2. Imagine the object as a ball attached to a string, being twisted around in a circle.  The string is pulling the ball towards the pivot.  The effect is that the ball is pushed outward as it keeps rotating...

It is easy to see that the pulling of the string is the cause of the ball pushing outward.  Therefore, pull comes before push.

---

Here is where I finally figured out why centrifugal force is fake.

If, for every action, there is an equal and opposite reaction, then the object being pulled upon also has an equal and opposite reaction.

For the sake of simplicity of this example, forget about circular motion.

You have a string with a ball attached.  You pull on the string, thus pulling on the ball.  Because there is an equal and opposition reaction not just for you, but for the ball as well... 

The reaction of your pull on the ball causes the ball to pull on you.  Thus, the ball isn't being pushed away from you when you pull on it, but you are being pulled towards the ball.

And, because of Newton's Third Law again, if you were to push on the ball, the reaction of your push on the ball causes the ball to push against you.  Thus, the ball isn't being pulled away from you when you push on it, but you are being pushed away from the ball.

Did you see what happens?  Apply that exact same logic back to the original diagram of circular motion.  Now do you see what happens?

The pivot point, which is "oneself" in the definitions of push and pull, transfers from the center axis to the object because of the equal and opposite reaction that take place. 

Therefore, the center axis pulling on the object causes the object to pull on the center axis.  

Did you notice that the word "push" is not in that statement?

That's because centrifugal force is fake.

---

Possibilities for discussion points:

1. Is there anything unclear, or anything left unanswered for you?

2. Does this explanation serve as a better way to help you understand why centrifugal force is fake?

3. Do you have any alternatives that also help to explain centrifugal vs. centripetal force?

(These are just suggestions, but I encourage you to post anything you think is relevant).

~ Miles

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Actually, centrifugal force isn't "fake." That's just a thing high school teachers say to their munchkins to simplify things. It's no more fictitious than gravity is, considering that gravity is really just the curvature of spacetime modeled as a force from our reference frame.

 

Anyway, the point is this. All you have to do is construct Newton's laws in a non-inertial reference frame, and you'll see centrifugal force appear bright as day.

 

It is true that centripetal force pulls a particle in towards the center of its curved path. From the reference point of the particle, though, a centrifugal force acts in the opposite direction, pulling outward. You use one or both depending on your perspective--but the two only coexist if you are not moving in your reference frame.

 

In an inertial reference frame, you have Force = mass × acceleration. The particle is accelerating toward the center, so the force is a pull inward to that center. It's nice, easy, and simple, so this is what teachers will tell you.

 

But in a non-inertial reference frame, however, you have: F + Fe + Fw + Fc = mass × acceleration. F is external forces, Fe is the force causing the non-inertial reference frame to rotate, Fw is the centrifugal force, and Fc is the coriolis force. If the particle is not moving relative to its own rotational reference frame, this means there is no external force, and the coriolis force is zero. So, those cancel out, and you get Fe = -Fw. In other words, there is a force Fw that is experienced by the particle which is opposite in direction to the force keeping the reference frame in rotation. The forces have to coexist to keep the particle from moving relative to its frame.

 

More simply, it's like this. If you're standing on the ground watching a car go around a corner, you recognize that the car is being pulled in by a force (friction) acting inward. If you're *in* the car, though, you're in an accelerating frame of reference, so the force you experience very clearly acts outward. You are at rest, and you're being pushed to the opposite side of the car by that force.

 

It's all about reference. Remember, everything is relative. As Einstein's theory of relativity would put it, that pull in the inertial reference frame is indistinguishable from a rotating reference frame with a centrifugal force applied. Which one you use depends on where you're basing your observations, so the simple way to think of it is as you said: centrifugal force pulls out, centripetal force pulls in.

Edited by Admiral Regulus
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Actually, centrifugal force isn't "fake." That's just a thing high school teachers say to their munchkins to simplify things.

 

All you have to do is construct Newton's laws in a non-inertial reference frame, and you'll see centrifugal force appear bright as day.

 

Centripetal force pulls a particle in towards the center of its curved path. From the reference point of the particle, a centrifugal force acts in the opposite direction, pulling outward.

 

It's like this. If you're standing on the ground watching a car go around a corner, you recognize that the car is being pulled in by a force (friction) acting inward. If you're *in* the car, though, you're in an accelerating frame of reference, so the force you experience very clearly acts outward. You're pushed to the opposite side of the car by that force.

 

It's all about reference. Remember, everything is relative. Which one you use depends on where you're basing your observations, so the simple way to think of it is like this: centrifugal force pulls out, centripetal force pulls in.

 

No.

 

You literally cannot define centripetal or centrifugal force without pivot.  Ergo, an object must be in circular motion in order for centrifugal or centripetal force to even be defined.

 

Plus, you completely contradict your own explanation.  You are totally right that everything is relative.  Which is exactly why pulling causes pulling, and pushing causes pushing.  That is a direct transfer of reference point.  

 

Centrifugal force is a push!  Not a pull!  This is caused by the necessary transfer of reference point due to Newton's Third Law stating "for every action there's an equal and opposite reaction" - ergo, there is an equal and opposite reaction for both the pivot point and the object.  

 

---

 

"Centripetal force" is actually just the effect of Newton's Third Law.  When you push on something, the equal and opposite reaction is that it pulls away from you.  But, since the inverse is always true: since one "equal and opposite reaction" causes another "equal and opposite reaction" to occur, when you push on something, it pushes back.  Thus, when you pull on something, it pulls back.  Therefore, pulling doesn't cause pushing, and pushing doens't cause pulling... but pulling causes pulling, and pushing causes pushing.  So, in terms of centrifugal vs centripetal force, when a center pivot point pulls on an object in motion, the object doesn't push away from center pivot, but the object pulls back on the pivot.  So, because centrifugal force is defined as pushing, it's fake.

 

---

 

Then, 

 

"Newton used the third law to derive the law of conservation of momentum; from a deeper perspective, however, conservation of momentum is the more fundamental idea (derived via Noether's theorem from Galilean invariance), and holds in cases where Newton's third law appears to fail, for instance when force fields as well as particles carry momentum, and in quantum mechanics."

 

>>> http://en.wikipedia.org/wiki/Newton%27s_laws_of_motion#Newton.27s_3rd_Law

 

"In a closed system (one that does not exchange any matter with its surroundings and is not acted on by external forces) the total momentum is constant. This fact, known as the law of conservation of momentum, is implied by Newton's laws of motion."

 

>>> http://en.wikipedia.org/wiki/Momentum#Conservation

 

So, Quantum Mechanics is a sub-field of Physics that is a closed system.  In an open system, centrifugal force is fake; in a closed system, it's real because the laws of physics are altered because of Quantum Mechanics.

 

---

 

Lastly, 

 

My OP is obviously not talking about closed systems.

 

~ Miles

 

P.S. 

 

In an open system (one that does exchange matter with its surroundings and is acted upon by external forces), the total momentum is not constant like it is in a closed system, and centrifugal force does not exist in an open system.

 

In a closed system (one that does not exchange any matter with its surroundings and is not acted on by external forces) the total momentum is constant, and centrifugal force exists because of momentum conservation.

 

Open systems allow for momentum to change.

 

A "Newton's Cradle," which is a closed system pendulum, displays centrifugal force because momentum is conserved.

 

Newtons_cradle_animation_book_2.gif

 

In my OP, the car and the ball examples are open system.  There is no hitting involved.  Momentum is fluid in an open system.  But, the pendulum constantly goes back and forth.  That gif shows centrifugal force in action in a closed system.

 

This is why I was focusing on open systems.  I was trying to keep my thread in laymen's terms for a wider audience.

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...you're kidding, right? This has nothing to do with Newton's third law. It's as simple as this:

 

1. If an object is not moving, the sum of all forces acting on that object must be equal to zero. (Newton's second law)

 

2. You are always where you are, right? The center of your perception is always going to be where you are, because you never move relative to you. From your point of view, you are always stationary. You never move relative to your reference frame.

 

3. Therefore, relative to you, the sum of all forces acting on your body must be equal to zero.

 

4. Now, suppose you are rotating, and a force is pulling you towards a given centerpoint. This is centripetal force.

 

5. Since you don't move relative to you, you must also simultaneously experience a force opposite of that given force. The opposite force is added to the original force, so that the sum can remain zero, as it should. This necessary opposite force is centrifugal force. It is real. You feel it. You experience it. You can measure it.

 

You know this is true because it can be applied to linear motion without changing anything. If you are accelerating in a car, there is a force pushing you forward, such that F = m a, where both F and a are nonzero. However, from your perspective, you don't move, so there must also be a force pushing you back in your seat, to keep you from moving relative to your perception. In this case, you have F1 + F2 = m a = 0, and consequently, F2 = -F1. There is a force, and a force opposing it that you feel against you.

 

And, you guessed it, this matches obvious observations. When you are accelerating forward, you do indeed feel a force pushing you backward. That's why. It's relative motion--something Newton didn't fully understand, but Einstein used to mold his fame.

 

I suggest you read up on planar rigid body kinematics, especially section 6.4, rotating reference frames. Chop chop! Final exam is next week at 7AM!

Edited by Admiral Regulus
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@@Admiral Regulus,

 

In an open system (one that does exchange matter with its surroundings and is acted upon by external forces), the total momentum is not constant like it is in a closed system, and centrifugal force does not exist in an open system.

 

In a closed system (one that does not exchange any matter with its surroundings and is not acted on by external forces) the total momentum is constant, and centrifugal force exists because of momentum conservation.
 

Open systems allow for momentum to change.
 

A "Newton's Cradle," which is a closed system pendulum, displays centrifugal force because momentum is conserved.
 

Newtons_cradle_animation_book_2.gif
 

In my OP, the car and the ball examples are open system.  There is no hitting involved.  Momentum is fluid in an open system.  But, the pendulum constantly goes back and forth.  That gif shows centrifugal force in action in a closed system.

This is why I was focusing on open systems.  I was trying to keep my thread in laymen's terms for a wider audience.

 

 Again,

It is not the same for open systems as it is closed systems.

The force that pushes outward in open systems is velocity, which is speed and momentum.

When something is in circular motion, velocity is at a 90 degree angle forward to the line of centripetal force at the speed of the rotation.  

It doesn't even need to be a full circle.  

Literally because of forward momentum and speed (velocity), centrifugal force is not equal to centripetal force in an open system, and as such it is fake.

~ Miles

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Uuummmm... that's not... :dash:

 

Right. Okay. So can you explain to me what relation either open systems or closed systems or momentum conservation have with reference frames?

Edited by Admiral Regulus
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I have to agree with Regulus on this.  Both centripetal and centrifugal forces are real and concrete forces.  There are two rather simple ways to demonstrate this:

 

1.) Newton's Third Law:  For every force there exist an equal and opposite force.  So if there is a centripetal force pointing inward, then by Newton's Third Law there must be a force of equal magnitude pointing outward, which would be your centrifugal force.

 

2.) Tether Ball:  Attach a ball to a pole with a string and kick the ball.  The string will pull taught and cause the ball to circle the pole.  I am sure everybody has seen some variation of this in person.  The thing is, the only way to pull a string taught is to pull both ends of the string in opposite directions.  If you apply a force in only one direction, the string will remain loose and simply accelerate.  So the only way this works is if the string is being pulled inward by the pole and outward by the ball.  Thus this everyday experience clearly illustrates the simultaneous existence of the centripetal and centrifugal forces.

 

 

 

One of the forces must come first as the origin of its equal and opposite reaction.

 

 

This is what is steering you in the wrong direction.  Newton's Third Law grants no such special privilege to one of the two forces involved.  The "for every force there is an equal and opposite reaction" wording of his Third Law is a rather clumsy and imprecise way to word it, hence the reason why I stated it the way I did above.  Both forces come into play simultaneously unless you are dealing with relativistic action at a distance type phenomenon, which we are not here. 

Edited by Twilight Dirac
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Uuummmm... that's not... :dash:

 

Right. Okay. So can you explain to me what relation either open systems or closed systems or momentum conservation have with reference frames?

 

Your previous post talking about "one's own self" as a single reference frame never changing is invalid, because you must take in mind the reference frame of the object you are interacting with itself as well.  If you don't, you are contradicting the fact that everything is relative.  

 

Second of all, you seem to be disregarding that I am talking about pivoting around an axis.

 

Lastly, if you had read the links I gave you, you would understand the difference between closed and open systems.  

 

I told you already, I know that closed systems have centrifugal force.  Look at the pendulum.  I posted that.  I know.

 

---

 

I shouldn't have to say this: 

 

Look at the picture in my OP.  What shape is it?  A circle.

 

Circular motion.

 

I'm not talking about linear; I'm talking about circular motion.

 

---

 

@@Twilight Dirac,

 

I've already covered everything you said.

 


 

Look folks, allow me right now to admit to having bad word choice.  It's not fake, but rather, fictitious.  I inadvertently didn't realize I was using fake when I meant to say fictitious.  Nonetheless...

 

I stand by my OP. 

 

---

 

Just... *sigh*

 

I don't have time at the moment to go into details.

 

Watch this.

 

https://www.youtube.com/watch?v=zHpAifN_2Sw

 

Please watch.

 

Thanks.

 

~ Miles

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In my head it was that both forces are real and they cancel each other out so you maintain orbit.

 

Although what I am studying is kiddy physics. I have only heard of force moving towards the center of orbit.

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Your previous post talking about "one's own self" as a single reference frame never changing is invalid, because you must take in mind the reference frame of the object you are interacting with itself as well.  If you don't, you are contradicting the fact that everything is relative.

 

 

Except that isn't necessarily true.

 

Draw a free body diagram of one body. There! Done! You have now modeled a system of one body without taking any other body into consideration.

 

 

Second of all, you seem to be disregarding that I am talking about pivoting around an axis.

 

What you don't realize is that it doesn't matter. There is nothing special about circular motion that cannot also be applied to other forms of motion. Circular motion is just a particular case of curvilinear motion, which is really the same as linear motion, but just with the extra consideration of more than just one dimension.

 

 

Lastly, if you had read the links I gave you, you would understand the difference between closed and open systems.

 

Except I didn't ask you what the difference was between open and closed systems. I asked you how open and closed systems relate to reference frames because you brought that up without any regard to why. It's like bringing up art styles in the 1200's in a discussion on AC circuits.

 

Until you can explain how this is all related, I'm going to assume you're just copying and pasting random crap from Wikipedia, kinda like what I did back in the seventh grade.

 

 

I told you already, I know that closed systems have centrifugal force.  Look at the pendulum.  I posted that.  I know.

 

The pendulum demonstrates conservation of momentum and conservation of energy. Nothing else, really. Both of those two things are very separate subjects from the coordinate substitution that I have been trying to explain.

 

As I said, you haven't explained the relation. I asked you to explain the relation.

 

In my head it was that both forces are real and they cancel each other out so you maintain orbit.

 

Although what I am studying is kiddy physics. I have only heard of force moving towards the center of orbit.

 

If the forces cancel out, you don't change velocity. An orbiting object is always changing velocity, so it does have unbalanced forces acting on it.

 

Draw a free body diagram of the moon in orbit around Earth. There is only one major force acting on the moon—that's gravity. That means the moon only accelerates towards Earth. Gravity pulls on the moon and causes its path to curve.

 

In order for an object to have a circular path, there must be a force acting inward. This force must be: F = m v2 / r, where v is the velocity and r is the radius to the center of the circle.

 

The force of gravity between two objects is given my FG = G* m * M / r2 where G is the universal gravitational constant, the m's are the masses of the two bodies, and r is the distance between them. Therefore, if m v2 / r = G* m * M / r2, the orbit will be circular. If the moon's velocity is too great, the moon will pull away from Earth. If the moon's velocity is too small, it will be pulled closer to Earth.

 

Gravity, in the sense that it keeps the planets in orbit, acts as a centrepetal force. Centrufugal force is something a little different. In order to understand this a little better, let's do a little thought experiment.

 

Suppose you go to sleep one night, and I kidnap you and put you in a large box. Before you wake up, I have a teleporter, and I could take you to any part of the universe you could imagine. You don't know where you are, or what's happening to you—you can't see through the box.

 

If you feel no forces acting on you at all, does that mean you're in space? The answer is no. It means you are moving with a constant velocity, and the same velocity that the box has. You could be in deep space, in orbit around a planet, or also free-falling to the surface of a planet.

 

But let's say that's not the case. Let's say you are being pulled to one end of the box by a "mystery force." So, what does that mean? Could you figure out the cause of that force? This could be a gravitational force, but it could also be some other kind of force acting on the box. If the box is moving forward, for example, you're going to be thrown to the back of the box by this mystery force.

 

If the box is rotating, that mystery force could be a centrifugal force. A force must act on the box for it to rotate, so from your perspective inside the box, you would feel a force pushing you toward the other end. To you, and to any instruments you have in your box, you would observe this centrifugal force as being no different from a gravitational force or a linear force. Without knowing if you're rotating, accelerating, or being pulled by gravity, you would have no way of distinguishing between any of those.

 

But let's say you are rotating. Let's also say you have a ball with you. You stand up so that the mystery force is pushing you feet down into the "floor" of the box. You drop the ball, and watch as it falls to the floor, like it would on Earth. Like Newton, you therefore conclude that there is a force pulling both you and the ball to the floor of the box. This force would be the centrifugal force.

 

The centrifugal force only exists in a rotating reference frame. It is the force that acts on objects to make them seem like they are moving from your perspective, when it is actually you that is moving. But from that perspective, it acts as any other force would.

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Watch this.   Please watch.

 

Remember, just because it has been posted on the internet doesn't mean its true.  I have taken the liberty of diagramming the merry-go-round pendulum experiment shown in this video

 

pendulum.png

This is rather similar to the diagram shown in the video linked above, only I haven't omitted half the forces acting on the string!  Honestly, this is quite the oversight.  You can clearly see where and how the centrifugal force arises, and as the video points out, because the string is under tension in all reference frames, the forces shown above exist in all reference frames.

 

About the only place I can agree with you here is in regard to semantics.  I did a quick wikipedia search and it gives two definitions for the centrifugal force.  One is a force present exclusively as a consequence of being in a rotating frame of reference which will by definition vanish in an inertial frame of reference, and the second is the badly named reaction centrifugal force which I have shown above, which is present in all frames of reference.  Regardless of what you name the forces, however, there is in fact a real, frame independent, outward pointing force present in both the above example and most rotating systems (exceptions occur for some purely action at a distance systems such as binary stars).  Call it whatever you want, but it exist, it is real, and it can do anything a real force can (perform work, break the string, have somebody drawn and quartered, etc.).

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(edited)

About the only place I can agree with you here is in regard to semantics.  I did a quick wikipedia search and it gives two definitions for the centrifugal force.  One is a force present exclusively as a consequence of being in a rotating frame of reference which will by definition vanish in an inertial frame of reference, and the second is the badly named reaction centrifugal force which I have shown above, which is present in all frames of reference.  Regardless of what you name the forces, however, there is in fact a real, frame independent, outward pointing force present in both the above example and most rotating systems (exceptions occur for some purely action at a distance systems such as binary stars).  Call it whatever you want, but it exist, it is real, and it can do anything a real force can (perform work, break the string, have somebody drawn and quartered, etc.).

 

Houston we have lift off!

 

Finally someone realizes!  It's pretty damn obvious, if you look through my history of posts (not just here), that I am a king of semantics.  I'm glad that finally someone understands; I am right; I am semantically correct!  

 

Lol, alright, enough cheering.  ;) 

 

You see, the issue I have with your post is that you still don't understand why your picture is showing a force that does not exist.

 

Semantically, centrifugal force, as you said, has two definitions.  There is reactive centrifugal force, and there is fictitious centrifugal force.

 

But the issue is that when you just, and only just, specify "centrifugal force" it refers to the fictitious one, because semantically, "reactive centrifugal force" is not "centrifugal force."  The cause of the confusion is due to the necessity to use the word "centrifugal" in "reactive centrifugal force."  Why?  

 

This:

 

Centrifugal = center fleeing

Centripetal = center seeking

 

Ergo, the etymology of the words are the reason that "centrifugal" is used in "reactive centrifugal force."  

 

Reactive centrifugal force is not the same force as centrifugal force.  It is a different force.

 

The current definition of "centrifugal force" states that it does not exist.

 

I've been trying to explain to you all, from the get-go, in my OP, that centrifugal force uses a non-inertial reference frame.  

 

The problem with that is not even because other reference frames don't see it (well, that's of course true, but I mean, the origin of the issue in itself is not that).  

 

The issue is:

 

The object is moving.  And, it is moving in a circle, of course.  

 

Ergo, "centrifugal force" refers to the one seen in circular motion.

 

---

 

(Hence why my OP is correct...)

 

---

 

@@Admiral Regulus, this is where you went wrong.  You made me switch over to something that semantically is not centrifugal force when I posted that pendulum (Newton's Cradle).  

 

So, Admiral, do me a favor and go to this page: http://en.wikipedia.org/wiki/Newton's_cradle

 

And, press "ctrl" + "f" to bring up the text finder, and type in "cent" --- you will see that neither centrifugal nor centripetal is mentioned on that page.  At all.

 

Because they both are semantically defined using circular motion.   :comeatus: 

 

---

 

Folks, you should start trying to realize that usually in academic subjects, and especially in physics, you need to know semantics.

 

My original post is indeed correct.  :twi: 

 

~ Miles

 

P.S.

 

The centrifugal force only exists in a rotating reference frame.

 

The reason I didn't reply to your post is because of ^that^ last thing you said.

 

You just proved me right.  Thanks.

 

:smug:

Edited by Miles
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Well if you don't disagree with me, then okay. I know I'm right, so therefore you are right, too. I don't understand any small bit of how you arrived at any of your conclusions, but all you seem to care about is semantics, so point taken. Quite frankly, I couldn't give two shits about that.

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You see, the issue I have with your post is that you still don't understand why your picture is showing a force that does not exist.

 

Semantics I will give you, this I will not.  Every force in that picture is as real as any force gets.  They exist in all frames of reference, are capable of doing work, deforming materials, accelerating objects, anything that a force can do those forces can do (although you might have to be clever as to your physical arrangements).   They are there and they are quite real.

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(edited)

Semantics I will give you, this I will not.  Every force in that picture is as real as any force gets.  They exist in all frames of reference, are capable of doing work, deforming materials, accelerating objects, anything that a force can do those forces can do (although you might have to be clever as to your physical arrangements).   They are there and they are quite real.

 

badaff16c4.png

 

---

 

To sort of synthesize some things I said in my OP into one collective thought:

 

Two forces of inward pulling are acting on the object in circular motion.  

(and now to pair this with your picture)

Tension in the string is caused by... inertia.

 

Those red lines you drew for centrifugal force are fictitious. 

 

---

 

Well if you don't disagree with me, then okay. I know I'm right, so therefore you are right, too. I don't understand any small bit of how you arrived at any of your conclusions, but all you seem to care about is semantics, so point taken. Quite frankly, I couldn't give two shits about that.

 

>>> "I couldn't give two shits about that."

 

*facehoof*

 

Then what are you doing on a thread about physics?  

 

Centrifugal force is fictitious.

 

My OP was never about reactive centrifugal force.  Reactive centrifugal force IS real.

 

Your comment about not giving a shit is keeping you from realizing:

 

Centrifugal Force and Reactive Centrifugal Force are two different things.

 

ERGO, semantics is 100% important in the realm of physics!

 

I'm not trying to be rude, I promise.  But you really have to take the names of things in physics with a semantically specific logic.

 

~ Miles

Edited by Miles
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Tension in the string is caused by... inertia.

 

Inertia isn't a force.  Inertia is simply something that must be overcome by force.  Sometimes the forces associated with overcoming inertia are called inertial forces, but as the name suggest, they are forces. 

 

 

 

Those red lines you drew for centrifugal force are fictitious. 

 

You keep saying that, but you have provided zero evidence to that effect.  We have the experiment in the video you posted that clearly shows a frame independent outward force, and to quote the old empiricist axiom "the measurement is the truth" then if you disagree with the experiment, it is the experiment that is correct.  Then there are all the examples I can provide, that outward force can stretch a spring outward, it can accelerate another object outward, you could replace the merry-go-round with another pendulum and form a bola for which the so called reaction force of one pendulum propagates through the string to become the centripetal force of the other.  Heck, just bolt a force meter to the bloody merry-go-round to take the measurement, or even suspend it above the merry-go round through a pulley system to keep the meter in an inertial frame, you will measure an outward force.  Then there is the small fact these forces are required to exist by Newton's third law.  That outward force satisfies every physics based definition for a force and you can't get rid of it through reference frame transformations, so I am not certain what else you want from it before you will accept it as a real force.

 

Perhaps if I pointed out how a fictitious force can arise through adopting a rotating reference frame you would better understand what is going on here.  Instead of starting with circular motion, start with mass moving with a fixed linear velocity, then switch to rotating frame of motion.  In the rotating frame of motion, that same mass will be undergoing curved motion and therefore accelerating.  We can then use Newton's Second Law to associate a force with that acceleration.  Here is your fictitious centrifugal force!  Notice how when we switch back to an inertial frame, both the curved motion and the force vanish entirely, and there is no evidence of an outward force in play at all.  No strings under tension that could pull springs outward or anything else like that, it is just gone.  Perhaps this is what is causing the confusion.

 

 

 

My OP was never about reactive centrifugal force.  Reactive centrifugal force IS real.

 

 

But those reactive centrifugal forces are the same ones shown in my diagram that you keep on insisting are fictitious.

Edited by Twilight Dirac
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>>> "I couldn't give two shits about that."

 

*facehoof*

 

Then what are you doing on a thread about physics?  

 

Centrifugal force is fictitious.

 

My OP was never about reactive centrifugal force.  Reactive centrifugal force IS real.

 

Your comment about not giving a shit is keeping you from realizing:

 

Centrifugal Force and Reactive Centrifugal Force are two different things.

 

ERGO, semantics is 100% important in the realm of physics!

 

I'm not trying to be rude, I promise.  But you really have to take the names of things in physics with a semantically specific logic.

 

~ Miles

 

It doesn't matter what you call it. What matters is that your calculations turn up the right answer in the end. You could take the same force and call it "Fspinnystuff" or "Fassbiscuit" for all I care. It's just an algebraic placeholder. Similarly, you could use a rotating reference frame or an inertial reference frame, that doesn't matter, either. Either method will lead you to the correct solution as long as you know what you're doing. You know, whether you do it with rdot squared times theta or v squared over r, it doesn't matter. It's the same difference. With F equals m times g or f equals m times negative g, again, it's the same difference. These things are all arbitrary.

 

I still don't know what you mean by reactive centrifugal force and centrifugal force that is, apparently somehow unreactive. And even more particularly, I've no idea how it relates to open systems, closed systems, and reference frames. I understand absolutely 0% of anything you said. I've tried to take a gander at it, but every other line contradicts itself so I gave up about two days ago.

 

So, to reiterate, I don't care. I know I'm right no matter what you say. I don't mean to sound arrogant, but I know I'm right because everything I've said is consistent with observations and can be applied to solve real-world problems. Whether or not I call it the thing you do is the concern of someone who... isn't me.

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@@Admiral Regulus,

I know you're probably getting tired of the back and forth... but, I just want to help you understand something.

Push = outward; move something away from oneself.
Pull = inward; bring something towards oneself.

When you have a ball on a string, and you spin it around, you are pulling.  Not pushing.
The ball creates tension because it is also pulling on the string.  Not pushing.

That is two centripetal forces.

The law is "equal and opposite," not "equal and inverse."

The equal and opposite force of the pivot point's centripetal force, is the ball's centripetal force.
The equal and inverse force of the pivot point's centripetal force, is the ball's centrifugal force.

The pivot point's centripetal force is from the ball towards the pivot point.

396ae7108b.png

 

The pivot point is pulling the ball towards the pivot point.

Then,

The ball's centripetal force is from the pivot point to towards the ball.

193579a886.png

The ball is pulling the pivot point towards the ball.

Those two centripetal forces are each other's equal and opposite.

---

The pivot point cannot have centrifugal force.  That is the reason why the "equal and opposite" force of the pivot point's centripetal force is the ball's centripetal force, as stated above.

Because:

(Here's where I'm going to show you how reactive centrifugal force is real)

9e82a52eaa.png

 

Now do you see the difference?

Now after studying that...

"In classical mechanics, a reactive centrifugal force forms part of an action–reaction pair with a centripetal force.
 

In accordance with Newton's first law of motion, an object moves in a straight line in the absence of any external forces acting on the object. A curved path may however ensue when a physical acts on it; this force is often called a centripetal force, as it is directed toward the center of curvature of the path. Then in accordance with Newton's third law of motion, there will also be an equal and opposite force exerted by the object on some other object,[1][2] such as a constraint that forces the path the curved, and this reaction force, the subject of this article, is sometimes called a reactive centrifugal force"', as it is directed in the opposite direction of the centripetal force."

The ball's own centripetal force's equal and opposite would be the ball's own reactive centrifugal force.

The pivot point (the axis) cannot have it's own centrifugal force, as explained in the image above.

The ball can.

---

Now, I know what you're going to assume.

>>> "You have blatantly contradicted yourself, Miles."

But, I haven't.

Because: Semantics.

~ Miles

P.S.

Just to clarify:

My OP does not talk about reactive centrifugal force.

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And this is why everything you said doesn't matter:

 

I could just as easily say there are only four forces acting in such a rotating ball scenario. Gravity, normal force, friction/drag, and tension.

 

Alternatively, you could model the entire system as a single rigid body rotating about a point not identical to its center of mass. Using the angular time derivatives and moment of inertia will give you the correct reaction forces acting on the system as a whole.

 

Call it whatever you want. After one too many petty arguments over semantics in the past, I refuse to go to that level. Stop digging in the mud on Wikipedia and open your eyes to the rest of the world.

Edited by Admiral Regulus
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After one too many petty arguments over semantics in the past,

 

Lmao.  

 

It was obvious in my OP that semantics were involved in this topic.  Otherwise I would not have used the definitions of push and pull.

 

For Pete's sake, Admiral, did you even read this bit?

 

And as soon as I asked myself those questions, I realized the answer through nothing other than the logic of semantics!

 

Push: To exert force on [something] in order to move it away from oneself.

Pull: To exert force on [something] in order to move it toward oneself.

 

Centripetal force is an inward pull; Centrifugal force is an outward push.

 

>>> "[...] through nothing other than the logic of semantics!"

 

---

 

You could have avoided this, Admiral. 

 

So I don't need any of your finger pointing.

 

I stated from the get-go that semantics were involved in my topic.   :proud: 

 

This is my topic; I defined the grounds upon which I wanted my topic to be based. 

 

There would not have been any back and forth as there was if I had based my OP in the math side of centripetal vs. centripetal, because then it would be about math - but I didn't, and it isn't.

 

You can say all you want about me, I don't care... But you should carefully read the starter posts of topics, as sometimes they will pre-define an aim that is not what you are assuming it to be.

 

~ Miles

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