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hms.tech
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I think that there is no such thing as centrifugal force .
Am I right ? is this force fictitious ?
Am I right ? is this force fictitious ?
Depends on how you're using the term centrifucal force. There's the fictitious centrifugal force in a rotating frame. A less common (for physicists) usage is "reactive centrifugal force", which is part of a pair of Newton third law forces: say a string exerts a centripetal force on an object, then the object exerts a reactive outwards force on the string. Note that this "reactive centrifugal force" is not exerted on the object itself, but on the string. In a rotating frame, the fictitious forces, centripetal and coriolis (and euler if there is angular acceleration of the frame) all appear to act on the object. Wiki articles:hms.tech said:I think that there is no such thing as centrifugal force. ... is this force fictitious ?
All forces are just mathematical models invented by humans.Studiot said:It doesn't exist.
"Fictitious force" is just an unfortunate name choice. It gives people the wrong idea that some forces are more "real" than others. But that is just philosophy, irrelevant to physics. That is why I prefer the terms "inertial forces" and "interaction forces".Studiot said:That is why it is fictitious.
A.T. said:All forces are just mathematical models invented by humans.
"Fictitious force" is just an unfortunate name choice. It gives people the wrong idea that some forces are more "real" than others. But that is just philosophy, irrelevant to physics. That is why I prefer the terms "inertial forces" and "interaction forces".
Studiot said:hms.tech
Before you get confusing explanations as to the different ways of regards motion under a central force or circular motion perhaps you would tell us what your course says ie which approach they take. Your exams will be based on this.
An "inertial" frame of reference means the frame of reference is not accelerating (no linear acceleration and no rotation). Newton's laws of physics apply in an inertial frame without any modification.hms.tech said:Yes, I read this word "inertial" a lot on the Wikipedia link provided by rcgldr. Can you explain this notion ?
hms.tech said:I couldn't find the term centrifugal force in any of my physics books, hence I checked out PF. Can you provide some links (non Wikipedia) about centrifugal force.
In your diagram of the car in a turn, there is a Newton third law pair of forces, an inwards centripetal force exerted by the road onto the car, and an equal in magnitude but opposing outwards reaction force that the car applies to the road. That outwards force is real, the issue for some people is using the term "reactive centrifugal force" to describe that outwards force that the car exerts to the road.hms.tech said:So it can be thought of as "inertia" , but I would stick to my claim that this force is non existent.
hms.tech said:Yes, I read this word "inertial" a lot on the Wikipedia link provided by rcgldr.
Can you explain this notion ?
rcgldr said:In your diagram of the car in a turn, there is a Newton third law pair of forces, an inwards centripetal force exerted by the road onto the car, and an equal in magnitude but opposing outwards reaction force that the car applies to the road. That outwards force is real, the issue for some people is using the term "reactive centrifugal force" to describe that outwards force that the car exerts to the road.
You switch frames back and forth and confuse the issue. Stick to an inertial frame, and there are no inertial forces. Stick to a non-inertial frame, and you always have inertial forces which act just like interaction forces (except Newtons 3rd).hms.tech said:Am I right in the above mentioned aspect ?
The centripetal force produces centripetal acceleration. The force that causes centripetal acceleration produces mechanical tensions (ie chains of electromagnetic forces at the atomic level). These mechanical tensions operate radially. The net sum of these tensions is the centripetal force that produces the centripetal acceleration.rcgldr said:An "inertial" frame of reference means the frame of reference is not accelerating (no linear acceleration and no rotation). Newton's laws of physics apply in an inertial frame without any modification.
If the frame was accelerating, such as a rocket in space, then to an observer inside the rocket, there would be an apparent force on any object within the spacecraft , similar to gravity on earth.
The wiki article on this goes into more detail:
http://en.wikipedia.org/wiki/Inertial_frame_of_reference
http://www.answers.com/topic/centrifugal-force
In your diagram of the car in a turn, there is a Newton third law pair of forces, an inwards centripetal force exerted by the road onto the car, and an equal in magnitude but opposing outwards reaction force that the car applies to the road. That outwards force is real, the issue for some people is using the term "reactive centrifugal force" to describe that outwards force that the car exerts to the road.
Because you are considering only the most trivial cases, like:Andrew Mason said:"centrifugal reaction force". As far as I can tell, this is a concept that serves no purpose
In the other thread we gave you plenty examples where a reactive centrifugal force exists.Andrew Mason said:two balls tethered to each other by a rope and rotating in space about their centre of mass,
The term "centrifugal" has nothing to do with producing acceleration. It simply means that the force points away from the center of rotation. Acceleration is a matter of net force, not just one centrifugal force.Andrew Mason said:It can produce no acceleration so it is hardly a centre-fleeing force as the term "centrifugal" would imply.
Sometimes it is, and sometimes it is not.Andrew Mason said:The true reaction to a centripetal force is another centripetal force.
A.T. said:Because you are considering only the most trivial cases, like:
In the other thread we gave you plenty examples where a reactive centrifugal force exists.
Yes, for local interactions the reaction to a centripetal force is always a centrifugal force. It's only when we invoke action at a distance (like Newton's gravity or a mass-less string that is not considered an object itself, just a means of force transmission) that we have a Newtons 3rd force pair of two centripetal forces.stevendaryl said:If a string pulls on an object, the object pulls back on the string. That's always the case, by Newton's third law. In the special case where the force of the string on the object is radially inward, the force of the object on the string is radially outward.
They extend the applicability of Newton's 1nd & 2nd to non-inertial frames. Which is a very useful thing, when you are actually using physics to compute something, not just muse about the beauty of laws.stevendaryl said:To me, "fictitious forces" are very ugly, because they spoil Newton's laws of motion.
Newton's 3rd doesn't apply to inertial forces, because momentum is not conserved in non-inertial frames. So we cannot extend Newton's 3rd to them.stevendaryl said:Where's the equal and opposite forces? There are none.
A.T. said:They extend the applicability of Newton's 1nd & 2nd to non-inertial frames.
A.T. said:Newton's 3rd doesn't apply to inertial forces, because momentum is not conserved in non-inertial frames. So we cannot extend Newton's 3rd to them.
stevendaryl said:That's not true. Momentum as a vector quantity is conserved in non-inertial frames. What isn't conserved are the components of momentum.
Yeah, you can always replace a simple approach with a mathematically equivalent, but more complicated one.stevendaryl said:Fictitious forces are not needed to extend Newton's laws to noninertial frames. What's needed is a more sophisticated notion ... basis vectors themselves are nonconstant... adopt a 4-D spacetime view...
That is quite true, but you are only looking at part of the picture. If there was only the object and the string you could not have a centripetal force acting on the object. There are necessarily other forces on the string.stevendaryl said:If a string pulls on an object, the object pulls back on the string. That's always the case, by Newton's third law. In the special case where the force of the string on the object is radially inward, the force of the object on the string is radially outward.
"Part of the picture" is fully sufficient for Newtons 3rd Law and local interactions. You don't have to consider all forces acting on a object or the net acceleration of the object, to tell that an individual force acting on it is centrifugal (points away from the rotation center) and forms a 3rd Law pair with a centripetal force acting on a different object.Andrew Mason said:That is quite true, but you are only looking at part of the picture.
So where is the concept of a centrifugal reaction force used? It cannot ever produce a centrifugal acceleration. So all it does is explain the tension.A.T. said:Because you are considering only the most trivial cases, like:
My quibble is not with the force per se but with the name "centrifugal" in conjunction with the term "force". A force is something that is capable of producing an acceleration of an object. The acceleration that this reaction force produces is always centripetal ie. opposite to the direction of the force.In the other thread we gave you plenty examples where a reactive centrifugal force exists.
From Wikipedia:The term "centrifugal" has nothing to do with producing acceleration. It simply means that the force points away from the center of rotation. Acceleration is a matter of net force, not just one centrifugal force.
A.T. said:"Part of the picture" is fully sufficient for Newtons 3rd Law and local interactions. You don't have to consider all forces acting on a object or the net acceleration of the object, to tell that an individual force acting on it is centrifugal (points away from the rotation center) and forms a 3rd Law pair with a centripetal force acting on a different object.
It's not a concept. The concept here is Newtons 3rd Law: A pair of equal but opposite force acting at the interface of two objects: one inwards (centripetal) the other outwards (centrifugal)Andrew Mason said:So where is the concept of a centrifugal reaction force used?
This describes the potential effects of the inertial centrifugal force as seen in the rotating frame.Andrew Mason said:From Wikipedia:
Centrifugal force (from Latin centrum, meaning "center", and fugere, meaning "to flee") is the apparent outward force that draws a rotating body away from the center of rotation.
Andrew Mason said:There is nothing about the "centrifugal reaction force" that causes anything to flee from the centre.