Centrifugal force

[gentleman-farmer]

swansont

Attractive forces allow the possibility of exerting a force that does no work, which occurs when the force is perpendicular to the motion. That solution is not present for a repulsive force.

 

gf) Centrifugal force is an example where the force does not lay in the inertial frame; and where the force is perpendicular to the motion. But all manner of work can be performed by the force.

 

swansont it would help if you were a little more specific -

 

gf

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[swansont]

swansont

 

gf) Centrifugal force is an example where the force does not lay in the inertial frame; and where the force is perpendicular to the motion. But all manner of work can be performed by the force.

 

swansont it would help if you were a little more specific -

 

gf

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Centrifugal forces are not examples of an attractive force. By definition of "centrifugal" (literally center-fleeing)

 

gf, it would be helpful if you were more correct.

[gentleman-farmer]

gf)

Centrifugal force is an example where the force does not lay in the inertial frame; and where the force is perpendicular to the motion. But all manner of work can be performed by the force.

 

swansont)

Centrifugal forces are not examples of an attractive force. By definition of "centrifugal" (literally center-fleeing)

 

gf, it would be helpful if you were more correct.

 

gf) I didn't give the example of Centrifugal force as an example of an attractive force nor did I suggest it - the example (as I stated) was one of a force perpendicular to the motion that can perform work

 

And that is a correct statement

 

gf

[D H]

Centrifugal force is an example where the force does not lay in the inertial frame; and where the force is perpendicular to the motion. But all manner of work can be performed by the force.

 

swansont it would help if you were a little more specific -

It would help if you were a little more specific.

 

Centrifugal force is a terribly overloaded and widely misused concept. The thing most widely referred to as the centrifugal force, [math]-m\,\boldsymbol{\omega} \times (\boldsymbol{\omega} \times \mathbf r)[/math], is a fictitious force. It cannot do any work because it is a fictitious force; fictitious forces cannot do work because they aren't real. The centrifugal force is not always perpendicular to motion. In any case, force that is always perpendicular to the motion cannot do any work by definition.

 

 

So you must have been thinking about some other force when you said that it can do all manner of work -- except you implied that you are thinking of the fictitious centrifugal force when you said "Centrifugal force is an example where the force does not lay in the inertial frame".

[swansont]

 

 

gf) I didn't give the example of Centrifugal force as an example of an attractive force nor did I suggest it - the example (as I stated) was one of a force perpendicular to the motion that can perform work

 

And that is a correct statement

 

gf

 

If your post was not a rebuttal of my statement, why would you bother to quote it? You doth protest too much, methinks. And, as D H points out, as a standalone statement, it's still wrong.

[gentleman-farmer]

DH

The thing most widely referred to as the centrifugal force, is a fictitious force. It cannot do any work because it is a fictitious force; fictitious forces cannot do work because they aren't real. The centrifugal force is not always perpendicular to motion. In any case, force that is always perpendicular to the motion cannot do any work by definition.

 

gf) Your statement is not thought out correctly :: centrifugal force is not called a fictitious force (or unreal as you say) because it doesn't exist - it is called fictitious because the force does not exist in the inertial frame. Our very existence on this planet owes its gratitude to centrifugal force and the resultant formation of the equatorial bulge (with a constant 295.25 gradient) that maintains axial stability.

 

Please look up centrifugal force and inertial frame - and it'll become clearer

 

By the same token swansont is in error also because he based his response on your faulty analysis

 

Here is an example :: the work is being performed along the line of the cable - while the inertia is in line with the hammer

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gf

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[D H]

Where is the centrifugal force in that picture, gf? Hint: The camera is not rotating with the hammer thrower. There is no centrifugal force in that picture.

 

Let's look at things from the perspective of the photographer. There certainly are forces at play here. The stone is subject to tension in the wire, and so is the hammer thrower. The hammer thrower is exerting a force on the wire, etc. etc. Just because forces are involved does not mean work is being done. For example, if the hammer thrower was rotating at a uniform rate, there would be no work. There is no work involved in uniform circular motion.

 

The trick here is that the hammer thrower's rotation is not uniform. He starts spinning slowly and quickly builds up a rapid rotation. Work is involved because the rotation rate is increasing. That's fairly easy to see from an inertial perspective. Computing work from the perspective of a frame that is rotating at a non-uniform rate is rather challenging. I suggest you try it.

 

BTW, this recent discussion of centrifugal force has nothing to do with the topic of this thread.

[gentleman-farmer]

C H

Where is the centrifugal force in that picture

 

gf) Your responses C H are always so jejune that I suspect you are an alien from Pluto

 

Where is the centrifugal force in that picture? It is in every pixel

 

 

C H

BTW, this recent discussion of centrifugal force has nothing to do with the topic of this thread.

 

gf) ask swansont he brought up the subject of

a force that does no work, which occurs when the force is perpendicular to the motion.

 

But a force perpendicular to the motion can do all manner of work - as we see in this illustration

 

gf

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[Cap'n Refsmmat]

You will note that the hands of the hammer thrower do not stay stationary. They move as he rotates. You can see this if you take a piece of string and try to spin it over your head -- your hands move in a small circle to cause the string to spin. However, the end of the string travels in a circle with one fixed center. Your hand holding the string moves around that center point. Thus, the force you apply to make the string move is not perpendicular to the motion, because your hand moves away from the center point and pulls on the string from an angle.

[swansont]

 

But a force perpendicular to the motion can do all manner of work - as we see in this illustration

 

 

Really? The cosine of 90º is not zero?

 

The force is not actually perpendicular to the motion, i.e. the cable is not straight, as the Cap'n has noted, giving us a tangential component of the force.

[gentleman-farmer]

You will note that the hands of the hammer thrower do not stay stationary. They move as he rotates. You can see this if you take a piece of string and try to spin it over your head -- your hands move in a small circle to cause the string to spin. However, the end of the string travels in a circle with one fixed center. Your hand holding the string moves around that center point. Thus, the force you apply to make the string move is not perpendicular to the motion, because your hand moves away from the center point and pulls on the string from an angle.

 

gf) It's not the hands that are of interest - they merely act as an extension of the cable. The point of interest is the inertial frame - the inertial frame (wherein lies the motion hence the momentum) is perpendicular to the line of force known as centrifugal force (which is quite real as the Olympic athlete clearly demonstrates)

 

swansont

Really? The cosine of 90º is not zero?

 

gf) Centrifugal force does not originate from the momentum of the hammer and has no relationship with the cosine of 90º -- centrifugal force originates from the time rate of change of the instantaneous straight line portion of the orbit as it goes curvilinear in accordance with Newton's 1st Law: a body in motion will follow a straight line unless acted upon by an external force

 

In this case the external force is being executed by the Olympic athlete

 

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gf

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[D H]

C H

 

gf) Your responses C H are always so jejune that I suspect you are an alien from Pluto

RIght back at ya, dude. You are the one with an overly simplistic view here.

 

And do stop with the C H (or more correctly, D H), gf) gf<newline>/ silliness. It just makes you look, well, hhmmm, what to say? If you can't say something nice ...

 

Where is the centrifugal force in that picture? It is in every pixel

The photographer is standing on the ground rather than rotating with the hammer thrower. That is ground in the foreground, not a rotating platform, after all. There is no centrifugal force in that picture.

 

 

[gentleman-farmer]

Cap'n Refsmmat

You will note that the hands of the hammer thrower do not stay stationary. They move as he rotates. You can see this if you take a piece of string and try to spin it over your head -- your hands move in a small circle to cause the string to spin. However, the end of the string travels in a circle with one fixed center. Your hand holding the string moves around that center point. Thus, the force you apply to make the string move is not perpendicular to the motion, because your hand moves away from the center point and pulls on the string from an angle.

 

gf) It's not the hands that are of interest - they merely act as an extension of the cable. The point of interest is the inertial frame - the inertial frame (wherein lies the motion hence the momentum) is perpendicular to the line of force known as centrifugal force (which is quite real as the Olympic athlete clearly demonstrates)

 

swansont

Really? The cosine of 90º is not zero?

 

gf) Centrifugal force does not originate from the momentum of the hammer and has no relationship with the cosine of 90º -- centrifugal force originates from the time rate of change of the instantaneous straight line portion of the orbit as it goes curvilinear in accordance with Newton's 1st Law: a body in motion will follow a straight line unless acted upon by an external force

 

In this case the external force is being executed by the Olympic athlete

 

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gf

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[D H]

Emphasis mine:

It's not the hands that are of interest - they merely act as an extension of the cable. The point of interest is the inertial frame - the inertial frame (wherein lies the motion hence the momentum) is perpendicular to the line of force known as centrifugal force (which is quite real as the Olympic athlete clearly demonstrates)

The highlighted phrase is nonsense for two reasons. One, the inertial frame is not normal to the line of force. I can't even begin to make sense of what you are trying to say here. Second, there is no centrifugal force in an inertial frame. You are mixing reference frames here, and that is a definite no-no.

 

Re your comment to swansont: Do you know what the definition of work is? Forces that are normal to the direction of travel cannot perform work. It is part and parcel of the definition of work. Also important to note, no work is done on an object that is not moving. That is also part and parcel of the definition of work.

 

 

A question for you: Is the hammer moving in the rotating frame in which the hammer thrower is stationary? What does the answer to that question say about work done on the hammer in that frame?

 

[gentleman-farmer]

C H (and others) Perhaps you'll see yourselves being laughted at in this cartoon - could I suggest you read it through carefully because it makes a point of every ill gotten notion you've all perpetrated - please take particular note in the line There's no such thing - as it was C H that started the There's no such thing drama that now you can see is quite real

 

"No Mr. Bond, I expect you to die!"

 

[D H]

please take particular note in the line There's no such thing - as it was C H that started the There's no such thing drama that now you can see is quite real

Where, exactly, did I say there is no such thing as centrifugal force? Please be careful: I did say the centrifugal force is a fictitious force and I did say that it is not a real force -- in the sense that (1) real forces are forces that not fictitious and (2) can be measured by some local experiment. I did not say that it does not exist.

 

And do stop with the C H nonsense. I don't know what you are meaning by that, but I suspect you are up to no good.

 

 

 

[swansont]

 

gf) Centrifugal force does not originate from the momentum of the hammer and has no relationship with the cosine of 90º -- centrifugal force originates from the time rate of change of the instantaneous straight line portion of the orbit as it goes curvilinear in accordance with Newton's 1st Law: a body in motion will follow a straight line unless acted upon by an external force

 

<sigh>

 

You said

But a force perpendicular to the motion can do all manner of work - as we see in this illustration

 

To which I replied

Really? The cosine of 90º is not zero?

 

There's nothing about centrifugal forces inherent to your original statement; a force perpendicular to motion can do no work, because of the definition of work (there's that pesky little dot product). End of story. You are flat-out wrong in your statement, and your example is not one of a force perpendicular to motion doing any work.

[gentleman-farmer]

[DJBruce]

What does the XKCD comic have to do with centrifugal force's ability to do work?

 

I am not a physics expert, but even I know that a force perpendicular to the motion of an object cannot do any work.

[gentleman-farmer]

DJBruce

I am not a physics expert, but even I know that a force perpendicular to the motion of an object cannot do any work.

 

Swansont)

force perpendicular to motion can do no work, because of the definition of work (there's that pesky little dot product). End of story. You are flat-out wrong in your statement, and your example is not one of a force perpendicular to motion doing any work.

 

gf) All of you DJBruce, Swansont, & D H, ( and I'm trying to say this as politely as the circumstances allow) have absolutely no knowledge of what you speak

 

It is impossible for a force to exist but what it has performed some work. Absolutely impossible

 

A force must encounter resistance in order to manifest itself. With resistance there must be deflection - with deflection there is distance traveled - with force and distance traveled - there is work. Work being Swansont's pesky little dot product - that he thinks no one understands

 

If you guys would think through what you are saying - you'd begin to understand centrifugal force

 

D H says

real forces are forces that not fictitious and (2) can be measured by some local experiment.

 

Gf) D H that is pure foolishness - centrifugal force was labeled "fictitious" for the sole reason that the force does not lay in the inertial plane. Stand in front of an advancing train (or stand in front of the Olympic athletes' hammer) and you'll learn all about inertial planes (and you'll learn about time rate of change of momentum)

 

With all other forces the inertia is in line with the force. Like as in don't put your hand where I'm about to drop this here rock.

 

Again - if a force exists it has performed some work - and it is the easiest thing in the world (in defiance of C H's suggestion that you can't perform a local experiment) to put a spring scale on the Olympic athlete's cable and watch the force increase as the athlete increases the speed of rotation (or vise versa)

 

 

gf

[Klaynos]

 

It is clear from this appeal to ridicule post that you do not want to continue taking part in this discussion.

 

I would suggest you re-read the rules for the forum, paying close attention to the section on negative personal comments.

 

Thread closed.