Coriolis and Centrifugal force visualized in a rotating mass(loop)

[D H]

A body's natural state of motion is along a geodesic, which in the absence of curved space-time, is a straight line. Once a body enters an area of curved space-time, ie feels the force of a gravitating mass, that body is accelerated towards the centre of that mass, ie it falls or followes a 'curved' geodesic. if its original speed is optimized to the force ( gravity is centripetal ) or acceleration, the result is a stable orbit.

 

There is no need for any other ( fictitious ) forces to account for this effect.

 

There is no need to bring general relativity into the picture when Mike doesn't even understand Newtonian mechanics.

 

There's even less of a reason to mix up the two concepts. One key difference between Newtonian mechanics and general relativity is that gravity is a real force in Newtonian mechanics but it isn't in general relativity. You mentioned both the force of a gravitating mass and geodesics. That is a very bad thing to do. Newtonian mechanics and general relativity are profoundly different ways of looking at gravitation. It is best not to mix the two.

 

 

This is keeping the accelerating as firstly by mathematical calculation of the movement towards the center . And Secondly by forces balanced surely.

 

Surely not.

 

There is no balancing force, and no balancing force is needed to explain an orbit from the perspective of an inertial frame in Newtonian mechanics. All that is needed is gravity.

 

Draw a picture of a small body orbiting a much more massive object. The standard picture has the small body moving along a curved path (a circle, ellipse, parabola or hyperbola) about the larger, central object. There's no balancing force here. There can't be. That orbiting body is following a curved path. That means it's velocity vector isn't constant, which in turn means it is accelerating. That acceleration vector always points toward the central body. The only force needed to explain this acceleration is gravity. There is no other force.

 

 

If there was no centrifugal force and you were free in an elevator but held above the earth you would feel the force of gravity pulling you into the floor of the elevator. If the elevator was now made to be circling the earth at approx 17,700mph the gravitational force would slowly be overcome by a force acting radially away from the center until the force of gravity was balanced. This would surely be described as centrifugal force, caused by the increase of orbital speed from 0 to 17,700 mph

 

Surely not again. There's a number of things that you are confused about here.

 

One is that you don't feel the force of gravity. The general relativistic explanation is quite easy. Gravity isn't a real force in general relativity, and the only things you can feel are real forces. That's going counter to my own advice not to invoke general relativity, so I'd best explain why you can't feel gravity from the perspective of Newtonian mechanics. Gravity, from a Newtonian perspective, acts so close to uniformly across every part of your body that you can't feel it.

 

Aside: You truly would feel gravity were the Earth millions of times more massive. Now gravity would not be close to uniform across your body. The tidal forces would act to pull your body apart. This is called "spaghettification." That effect still does exist for our puny little Earth, but it's so ridiculously small that you cannot feel it.

 

So what do you feel as "weight"? The answer is that you feel everything but gravity. You aren't feeling gravity when you are standing in that elevator car. You are instead feeling the elevator floor pushing up on your feet. You feel that upward push by the floor, not the downward pull by gravity. That upward force propagates throughout your body, and you feel that too. You do not feel gravity. An astronaut on the International Space Station feels weightless not because gravity is non-existent (it's about 89% of Earth surface gravity) but rather because the only force acting on that astronaut is gravity.

 

Suppose you wake up, rather woozy, and find yourself in what looks like an elevator car. You try to remember how you got there. You remember a party last night, but then what? Suppose that unbeknownst to you, that party was hosted by Bug Eyed Monsters. Yep. You've been abducted by aliens and are now far, far away from the Earth in a spaceship accelerating at 1g. The aliens have merely secured you in a room that looks like an elevator car; they'll leave you there until they have time to experiment. You're not anywhere close to a gravity field, yet you feel normal weight. That's because of the spacecraft's acceleration. What you feel as weight isn't gravity. It's everything but gravity.

 

 

Now let's switch gears to another thought experiment. Imagine taking a slow ride all the way up a space elevator. The top end of the space elevator is well beyond geosynchronous orbit . We'll ride all the way to the top. You feel your normal weight as you start the ascent (it's a slow climb). Eventually you'll notice that you are feeling lighter and lighter. By the time you reach geosynchronous altitude you feel completely weightless. Once you pass geosynchronous altitude you start feeling pulled toward the ceiling. You'll need to stand on what previously was the ceiling to continue the ride to the top. Your feeling of weight now start to increase as you climb ever higher.

 

During the first part of the climb that force from the elevator floor is upward, so by definition it's a centrifugal force. This is just a kinematic classification of a real force, in this case, it's the normal force that keeps your body from falling into the floor during the first part of the climb. Note that this normal force becomes a centripetal force once you climb past geosynchronous altitude.

 

There is no need to invoke a fictitious balancing force to explain your motion, or what you feel. From the perspective of an inertial observer, the only forces acting on you are that of gravity and the normal force. Note that the normal force vanishes when you reach geosynchronous altitude. At this point, the only real force acting on you is gravity. Period.

 

What about from the perspective of an Earth-fixed observer? Yes, now you can explain a geosynchronous orbit using the concept of the fictitious centrifugal force. However, from this perspective, a geosynchronous satellite isn't moving. It's standing still. Invoking the fictitious centrifugal force to explain orbits is wrong for a number of reasons. One is that the object isn't "orbiting". It's standing still. How is that an "orbit"? Another is that this explanation fails in the more general case of an elliptical orbit (or a parabolic or hyperbolic trajectory).

 

There's no need to invoke the fictitious centrifugal force, and doing so obscures the true picture of what "orbit" means.

[photon propeller]

I think the difference here is how one envisions gravity. Not just as the curvature of space time, but a dynamic gravitational depression with longitudinally oscillating gravity waves, torsion waves, on a gyroscopic plane. Isnt the gravitational depression in space time not just under the mass (as typically pictured), but on top , to the sides, literally from all directions spinning towards the center? Shouldnt the center of that depression be the center of the mass? One may be able to make some proper predictions but until gravity is completely defined we cannot make them all. Gravity is currently defined as completely radial but current study on gravity waves reveal torsion. ECT is being realized.

[D H]

That makes no sense. It's just a mishmash of buzzwords. Try putting some math behind those buzzwords. Even better, how about some predictions of experimental outcomes that will differentiate your buzzword physics from the current understanding of gravitation?

[MigL]

I suppose you're right D.H., mixing GR and Newtonian gravity can lead to confusion, but I've had numerous conversations with Mike and he picks up things pretty quick. I just thought I'd cover all bases and use both models to describe the same effect.

The main point is that gravity, whether real ( Newtonian ) or fictitious ( space-time curvature in GR ) is the only active force and is centripetal in nature ( force vector is always pointing in ).

Edited May 23, 2013 by MigL

[Mike Smith Cosmos]

I suppose you're right D.H., mixing GR and Newtonian gravity can lead to confusion, but I've had numerous conversations with Mike and he picks up things pretty quick. I just thought I'd cover all bases and use both models to describe the same effect.

The main point is that gravity, whether real ( Newtonian ) or fictitious ( space-time curvature in GR ) is the only active force and is centripetal in nature ( force vector is always pointing in ).

 

EXPLAIN THE ARROW FORCE

 

.

 

.I am oblivious of anything outside my box. All I know is "I am hanging on for grim death". And can feel a force of some sort going from my head to my feet. I know of no universe, or anything else for that matter. What is this force I feel ?

I seem to be locked into some form of dizzy motion thats trying to drag me somewhere away from my hand ? It is not fictitious to me !

Edited May 24, 2013 by Mike Smith Cosmos

[D H]

EXPLAIN THE ARROW FORCE

 

. Centraf Toy.jpg

 

.I am oblivious of anything outside my box. All I know is "I am hanging on for grim death". And can feel a force of some sort going from my head to my feet. I know of no universe, or anything else for that matter. What is this force I feel ?

I seem to be locked into some form of dizzy motion thats trying to drag me somewhere away from my hand ? It is not fictitious to me !

 

The platform in that diagram is depicted as spinning, so it is presumably drawn from the perspective of an inertial observer. From that perspective, there is *no* centrifugal force acting on any of the people in that diagram.

 

Regardless of the frame of the observer, not one of the people in that diagram feel an outward force. What they do feel is an inward (centripetal) force.

 

The centrifugal force is a fictional device used to extend Newton's second law from the inertial frames in which it is valid to rotating frames (where strictly speaking, Newton's second law is not valid). You cannot feel the fictitious centrifugal force because it's a fiction. A very useful fiction, but still a fiction.

[studiot]

Mike, it might help to consider the question

 

If a person on the edge of your roundabout dropped a ball, we all know it would fly off. But in which direction? tangentially or radially or in some other direction?

 

It is perhaps easier to rephrase as

 

If I whirl a stone around my head on a string and suddenly cut the string, which way will the stone go?

Edited May 24, 2013 by studiot

[Mike Smith Cosmos]

Mike, it might help to consider the question

 

If a person on the edge of your roundabout dropped a ball, we all know it would fly off. But in which direction? tangentially or radially or in some other direction?

 

It is perhaps easier to rephrase as

 

If I whirl a stone around my head on a string and suddenly cut the string, which way will the stone go?

 

Yes well that'.s the classical answer and reality " It goes off tangentially at the point of CUT "

 

But the problem is the 'mass or me in the box ' wants( by inertia to go in a strait line all the time," but I am being pulled constantly by the fulcrum and its connecting pieces into a circle ( this is the centripetal force as I understand it. ) .It is succeeding to do that,( pull me out of a strait line ) in some form of acceleration radially ( although I dont move up the radius at all. ) Though the F=ma means there is a force . radially inward ( centripetal) . But surely as I am not going up (in ) the radius there must be a reactive force outward to Balance ( Namely the centrifugal force. )

 

Is this not the same as pushing , or attempting to push a very large block on a surface . Push is forward Pushing force Resistance is the Frictional Force.

 

If I was left to my own devices, I would be saying " Centrifugal force is the reactive force experienced when we try to move MASS off a strait line trajectory ." And " that this Centrifugal force can have many effects when mass moves in a restrained circle"

 

When I swing a Bucket over my head half full of water, the water stays in the bottom of the bucket, when the bucket is both below , sideways or above my head.

 

When a Satellite moves in Low Earth Orbit . Gravity is the force pulling down radially towards the Earth.( Centripetal Force.) Centrifugal Force is surely the reactive force caused by gravity pulling the satellite away from a strait line into a circle ? ( like the swinger of the bucket of water , pulling (like Gravity on the Satellite) .

 

I really don't understand why we can not accept Centrifugal Force as we accept a lot of other forces. ( Some originating, others reacting.)

Edited May 24, 2013 by Mike Smith Cosmos

[studiot]

But surely as I am not going up (in ) the radius there must be a reactive force outward to Balance ( Namely the centrifugal force. )

 

This is the whole crux of the matter.

 

I said, in my first post in this thread, that the rotating object is not in equilibrium.

 

It cannot be or it would not be accelerating.

 

It must be accelerating because it's motion is deviating from a straight line.

 

Because it is accelerating it must be subject to a resultant or unbalanced force.

 

Or because it is not in equilibrium is must be subject to an unbalanced force and therefore it must be accelerating.

 

This acceleration is called the centripetal acceleration because it is directed towards the centre of rotation.

 

So I repeat no balancing outward force is required, in fact one cannot be present.

 

*************************************

 

You can, however reduce the analysis from one in Newtonian dynamics to a (often) simpler one in statics by introducing a fictitious balancing force called centrifugal force. In this analysis nothing is then considered to be accelerating.

Edited May 24, 2013 by studiot

[Mike Smith Cosmos]

*************************************

 

You can, however reduce the analysis from one in Newtonian dynamics to a (often) simpler one in statics by introducing a fictitious balancing force called centrifugal force. In this analysis nothing is then considered to be accelerating.

 

Is this latter description not similar to my explanation above in my last post . Accept that I did mentioned acceleration. But I did say it was not going anywhere up the radius. I have never been too keen on the acceleration term because nothing seemed to be going anywhere up the radius. I suppose if you think of it relative to the projected strait line trajectory, it would be an acceleration away from that straight line trajectory.

 

I did measure the cenrifugal force , using a sensor in the radius as it was swung in a partial arc. This in my final year project at University Degree.

 

Edited May 24, 2013 by Mike Smith Cosmos

[studiot]

Is this latter description not similar to my explanation above in my last post . Accept that I did mentioned acceleration

 

Not at all similar, no.

Yes you mentioned acceleration and that is the problem. I said that none exists if you apply a balancing force.

 

That is a definition of a balancing force.

 

 

 

But the problem is the 'mass or me in the box ' wants( by inertia to go in a strait line all the time," but I am being pulled constantly by the fulcrum and its connecting pieces into a circle ( this is the centripetal force as I understand it. ) .It is succeeding to do that,( pull me out of a strait line ) in some form of acceleration radially ( although I dont move up the radius at all. ) Though the F=ma means there is a force . radially inward ( centripetal) . But surely as I am not going up (in ) the radius there must be a reactive force outward to Balance ( Namely the centrifugal force. )

 

You did, however, correctly identify that the centripetal force pulls the rotating mass away from its inertial straight course, inwards towards the centre of rotation.

 

Unfortunately you are also mixing up motion and acceleration. Motion (velocity) is a vector and has direction as well as magnitude. Change of either of these constitutes acceleration.

 

What you are suggesting is because the radius is not changing there must be a balancing force.

 

This is not so. The mass accelerates because it deviates its course from a straight line to maintain a constant radius.

 

This deviation requires a net force to be acting or there could be no acceleration. If the centripetal force is 'balanced' by another, how could the acceleration be generated?

 

Since you correctly answered my last question here is a more tricky one that an engineer ought to be able to answer.

 

A 100lb mass is attached to one end of a 1 ft substantial chain and the other end anchored at a pivot. A second mass of 1lb is attached to the larger one by means of a single 1 inch link that breaks at a force of 10 lbs.

 

The whole assembly is set in motion, rotating about the pivot as shown in the diagram.

 

What are the forces on the link and when will it break?

Edited May 24, 2013 by studiot

[Mike Smith Cosmos]

Not at all similar, no.

Yes you mentioned acceleration and that is the problem. I said that none exists if you apply a balancing force.

 

That is a definition of a balancing force.

 

 

 

 

You did, however, correctly identify that the centripetal force pulls the rotating mass away from its inertial straight course, inwards towards the centre of rotation.

 

Unfortunately you are also mixing up motion and acceleration. Motion (velocity) is a vector and has direction as well as magnitude. Change of either of these constitutes acceleration.

 

What you are suggesting is because the radius is not changing there must be a balancing force.

 

This is not so. The mass accelerates because it deviates its course from a straight line to maintain a constant radius.

 

This deviation requires a net force to be acting or there could be no acceleration. If the centripetal force is 'balanced' by another, how could the acceleration be generated?

 

Since you correctly answered my last question here is a more tricky one that an engineer ought to be able to answer.

 

A 100lb mass is attached to one end of a 1 ft substantial chain and the other end anchored at a pivot. A second mass of 1lb is attached to the larger one by means of a single 1 inch link that breaks at a force of 10 lbs.

 

The whole assembly is set in motion, rotating about the pivot as shown in the diagram.

 

What are the forces on the link and when will it break?

rotator1.jpg

 

What are you trying to do to me ? My calculator is up in the attic with the teddy bears, for when the grandchildren come I spend my days painting Trilobites, and thinking about where all the calcium comes from to make up their calcite eyes. Over here , we work in the MKS ( meters Kilograms seconds system ) [ which incidently just happens to be my initials Mike Keith Smith].Not Feet pounds and Busshels. And I cannot seem to get the Parrafin powered generator going to make the gears in my brain turn in the maths part of my brain. I have difficulty trying to remember where I put the tea caddy. With concepts and pictures I am as bright as a button. Anyway I have had a go. The answer is Approx 3 ( feet per sec) (meters per Second) .

My Reasoning and Calculations follow.

 

As far as the outer device . Small one inch link under question, the inner device is just a device for moving ME the small chain and small weight around. ( being 100 times mass )

 

ME the small mass is effectively being moved around a circle of radius one foot one inch , having a mass of one pound.

Which by my crude reconing is ( 2.5 or 2.25 lbs to kiliogram is somewhere like 0.44 to .5 kg per pound) CREEK GROAN !) and as the radius is 1.1 feet and it is approx ( 39 inches = 1 meter , so one inch = 1/39= .0.025641 meters so one foot =12" = 0.3 meters ) CREEK GROAN

 

NOW BY MY RECONING THE FORCES ON THE LINK ARE Centripetal IN Centrifugal out = m x Vsquared/ r

 

 

m = 1 pound = .44 to .5 kgms v we do not know yet r= 1ft one inch ( just a minute I will look at my foot ) = 1 ( approx 1.1foot x 0.3meters= .0.33m)

GROAN CREEK .

 

Caculations below seem to come out APPROX THREE meters per second or 3 feet per second ( apprximations are BAD ( need to go up in the roof among the teddy bears for the granchildren and find my calculator, or slide rule.

 

I need to go and lie down ! Where are the Asprin ? Or go and think about Calcite and Trilobites Eyes !

 

 

AHH ! THIS IS BETTER

 

 

 

 

.

Edited May 25, 2013 by Mike Smith Cosmos

[studiot]

If imperial measure offends you, then call them all kg and metres - the numbers don't matter it is the principles that count.

 

And the principle you have correctly observed is that the larger, 100unit , mass does not exert a centrifugal force on the breakable link.

 

So why should the smaller 1 unit mass exert a centrifugal force on anything?

Edited May 25, 2013 by studiot

[Mike Smith Cosmos]

If imperial measure offends you, then call them all kg and metres - the numbers don't matter it is the principles that count.

 

And the principle you have correctly observed is that the larger, 100unit , mass does not exert a centrifugal force on the breakable link.

 

So why should the smaller 1 unit mass exert a centrifugal force on anything?

 

Correct ! But the forces going on down there in the 100 LB weight and the Heavy Chain SWISHING ABOUT are HUMUNGOUS ! I used to take physics students out on a deserted Foot ball field . They had a 8 meter strong rope with a 5 Kgm weight ( suitably padded) . I would get a strong male to swing by cranking up small radius to all 8 metres. . The rest would stand well back . I would shout ( as the student staggered about at the middle. " CAN YOU FEEL THE FORCE " YE-E-E S MR SMITH as he staggered and fell dizzy to the earth. Please Sir can I have a Go ? They loved it AND THEY FELT THE FORCE WHAT FORCE DID THEY FEEL ?

 

 

Surely he can feel the force of trying to break/ convert inertia from a straight trajectory with all that momenum into a circle with angular momentum . FEEL THE FORCE

Edited May 25, 2013 by Mike Smith Cosmos

[studiot]

You are asking what a rotating body 'feels'.

 

Try this.

 

Consider a rotating chain.

 

Start at the first link by the pivot.

 

The first link 'feels' a centrally directed inward force - the centripetal force.

 

So it pulls inwards on the second link, to which it is attached.

 

The second link therefore 'feels' an inward pull , so it exerts a reaction force on the first link which is also a pull, by Newtons third law.

 

In turn the second link pulls inwards on the third link; it does not, however, push outwards on the third link. In turn it receives a reactive pull from the third link.

 

This process continues all the way up the chain to the outer link.

 

The outer link, or weight or whatever has no attachment further out so does not pull inwards on anything.

 

No animals were harmed in the production of this post and no centrifugal force was involved.

 

Edited May 25, 2013 by studiot

[D H]

Is this latter description not similar to my explanation above in my last post . Accept that I did mentioned acceleration. But I did say it was not going anywhere up the radius. I have never been too keen on the acceleration term because nothing seemed to be going anywhere up the radius. I suppose if you think of it relative to the projected strait line trajectory, it would be an acceleration away from that straight line trajectory.

 

This is the crux of your problem. For some reason you cannot accept the fact that acceleration does not necessarily change radial distance. Acceleration is a vector, not a scalar. The acceleration vector represents the rate at which the velocity vector is changing. If some object is undergoing uniform circular motion the acceleration vector always points toward the center of the circle along which the object is traveling. This is a mathematical necessity.

 

Now let's apply Newton's second law. Given an object in uniform circular motion, the net force on that is necessarily centripetal. No centrifugal force is needed.

 

 

I did measure the cenrifugal force , using a sensor in the radius as it was swung in a partial arc. This in my final year project at University Degree.

 

centrifugal exp.jpg

 

No, you didn't. Look at your diagram. Draw a free body diagram. What centrifugal force do you think you measured? What you measured was a centripetal force.

Edited May 25, 2013 by D H

[Mike Smith Cosmos]

You are asking what a rotating body 'feels'.

 

Try this.

 

Consider a rotating chain.

 

Start at the first link by the pivot.

 

The first link 'feels' a centrally directed inward force - the centripetal force.

 

So it pulls inwards on the second link, to which it is attached.

 

The second link therefore 'feels' an inward pull , so it exerts a reaction force on the first link which is also a pull, by Newtons third law.

 

In turn the second link pulls inwards on the third link; it does not, however, push outwards on the third link. In turn it receives a reactive pull from the third link.

 

This process continues all the way up the chain to the outer link.

 

The outer link, or weight or whatever has no attachment further out so does not pull inwards on anything.

 

No animals were harmed in the production of this post and no centrifugal force was involved.

 

You are using a lot of " math Descriptors" . I am asking about the Student in the middle of that horrendous spinning Rope and weight. I know because I have done it. IT pulls with one h... of a force. Look at the scottish highland games . The Mc tavish has to nearly lean over backwards. the wee.

 

 

This thing is away on me , the noo. Its pulling me nearly over the wee thing , jock, jimmy mac lad ! the noo !

[studiot]

You have not yet addressed my question as to why there is no outward push (as you earlier asserted) on any link in my chain or any object attached to it.

[Mike Smith Cosmos]

You have not yet addressed my question as to why there is no outward push (as you earlier asserted) on any link in my chain or any object attached to it.

I am not quite sure what you are asking me ? My fault not yours ?

[D H]

You are using a lot of " math Descriptors" .

 

I'm using math because that is the language of physics. If you can't understand that language you are at a bit of a disadvantage.

 

 

I am asking about the Student in the middle of that horrendous spinning Rope and weight. I know because I have done it. IT pulls with one h... of a force. Look at the scottish highland games . The Mc tavish has to nearly lean over backwards.

 

Rhetorical question: Can you push a rope and expect a force to be transmitted to the other end? The answer is of course not. Ropes are flexible. A rope under tension can transmit a force, but only in one direction.

 

So what kind of force does one of those hammer throwers experience? First, look at the kinematics of the throw. The thrower and hammer are connected to one another via a rope or cable, and both are rotating about their common center of mass. The force on the hammer is directed toward the thrower, and hence toward the thrower/hammer center of mass. This is a centripetal force. The force on the thrower is directed toward the hammer, and hence toward the thrower/hammer center of mass. This also is a centripetal force.

 

There is no centrifugal force here.

[studiot]

I am not quite sure what you are asking me ? My fault not yours ?

 

It's not a question of fault.

 

In your post#30 you presented a guy on a green box facing the edge of a roundabout, and subject to a red arrow from the roundabout (not the one on the green box).

 

That, sir, is a push.

 

When I asked if the large weight could push onthe next link outwardsI think you accepted it could not and does not.

 

So I ask again where or why you think the end of a rotating arm could exert a push on anything.

 

If a piston was spinning in a cylinder would it exert a radial push outward on the bore?

[MigL]

Mike, your students were not feeling the strain of a force acting on them, but the strain of having to exert a force on the spinning mass. Just semantics, but it makes a big difference.

[swansont]

They loved it AND THEY FELT THE FORCE WHAT FORCE DID THEY FEEL ?

 

They felt the reaction force to the centripetal force they were exerting on the weight. But they did not feel a centrifugal force (how could they? they were already at the center), and neither did the weight.

[studiot]

Mike, does this help?

 

http://www.explainthatstuff.com/centrifuges.html

[Mike Smith Cosmos]

Mike, does this help?

 

http://www.explainthatstuff.com/centrifuges.html

 

Right, I have read most of the Link. My whole 'intuition' feels there is something wrong here.

 

 

The man is in a closed box. He is unaware what is happening outside the box. He is gripping the stout rope. Unbeknown to him there is a very large roller at the end of his rope. The whole platform is turning in a large circle anticlockwise. The large roller is gently persuaded to move with the platform turning. It gets faster and faster. The roller is free apart from the ridges.

 

What happens to the roller , (black ) ? the Rope. ? The Man holding the rope. ?

 

 

Edited May 25, 2013 by Mike Smith Cosmos