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Swinging the Lead - Debunking Centrifugal Force

old man emu

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When we see yo-yos on their strings, people stuck on the walls of a carnival ride as the floor is pulled away, laboratory centrifuges, even this,


we imagine that there is some force acting to hurl water, dare-devils, and blood cells away from the centre of the spin. Of course, there should be, because Newton told us for every force, there is an equal and opposite force. The force should have a name that tells us something about it, so we call if centrifugal force, which simply means “away from the centre”. So, there must be an opposing force, and the is. We call it centripetal force, which means towards the centre.


It is logical. We have felt it when we have been in carnival rides. It makes us feel like we are being thrown outwards. It’s what makes stuff slide across the top of the dashboard when your car goes around a corner. You’ll tell me it’s real enough.


But I’m going to SHOW you that it is all in your mind. Despite your many observations of things seeming to be thrown outwards from a rotating object, physicists can show that no such thing as centrifugal force exists in our Universe.


This is the beginning of an article I am writing at the moment. It's taking some time to get the research done and expressed in a readable way, so stay tuned.

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6 hours ago, old man emu said:

So, there must be an opposing force, and the is. We call it centripetal force, which means towards the centre.

I thought I had that when I was a kid. My dad and I were heading down the paddock in the old '46 Maple Leaf Chev truck. I was riding on the driver's side running board and hanging onto the door. There was a sharp 90 degree left hand bend coming up, so I thought I'd let go and see if I could go round the corner without hanging on. The truck went left and I went straight ahead and face planted in the paddock. I was picking bullhead prickles out for days and have never believed in centripetal force since that day.

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Opinion, opinions, opinions. No one has yet shown the existence of  this thing labelled "centrifugal force" by the application of the Scientific Method


I agree that the word "centrifuge" as a noun - name of a thing, or as a verb - to separate by spinning, is useful in layman's terminology. However, in the language of Physics, the adjective "centrifugal" describes something that is non-existent.


8 hours ago, onetrack said:

I own a centrifugal pump, and it pumps water just fine - utilising the centrifugal principle.

No doubt you do. And I have a washing machine that removes water from the clothes by spinning. But while the principle might be called "centrifugal", that is nothing more than a name.  “What’s in a name? That which we call a rose / By Any Other Name would smell as sweet.” 


I challenge anyone to prove, by scientific method, that such a force, and it must be a real force capable of being measured, can be proved. It is said that one cannot prove a negative. Claiming that it is impossible to prove a negative is a pseudo logic, because there are many proofs that substantiate negative claims in mathematics, science, and economics, Nevertheless, whoever makes a claim carries the burden of proof regardless of positive or negative content in the claim.


All I say is,  jerry maguire money GIF 


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Is not the second law of thermodynamics only "provable" by lack of contrary examples? Like how heat just does not flow from cold to hot?

If you do not deny centripetal force, how can its equal and opposite reaction not exist? What force caused the tape to come off my prop? ( 7000g's at the end of a Jabiru prop).

Yes I certainly see how centripetal force is required to keep a circulating object from flying off at a tangent and how this manifests itself as tension in the string, but why not say that the weight at the end is exerting a centrifugal force on the string?

Here though is the most amazing thing... there is NO WAY to discern any difference between that force and gravitational attraction. The only explanation of this is that gravity consists of the warping of space-time...  wow, its too hard for me to figure out. What about the exchange of gravitons ?  But how can gravitons exist in a spin drier?

And I thought Jabiru maintenance was hard.

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This post comes with no guarantees but this is what I remember of this subject.     I haven't yet looked this up and I am more than happy to be contradicted



If we have a ball on a piece of string and we swing it around our head, we know what happens, we can feel our hand being pulled outwards, this is what is described as centrifugal force. For the most part this explanation works ok in practical situations.    What is actually happening?  The ball has velocity that we impart by swinging it around. Because of inertia the ball wants to travel in a straight line.   It is the force applied by the string that is working to change the course or accelerate the ball (in a different direction) that we can feel as an outward force.  If we swing faster, the balls tendency to want to travel in a straight line is enhanced or to put it another way the force required to change its direction is greater. If the string breaks then the outward pull on our hand vanishes and the ball will travel off in a straight line.    I guess the question is, is there a distinct force that is pulling the ball away from the centre or is is there force imparted on the string  by a ball that naturally wants to travel in a straight line.


In practice though it is like gravity is the curving of space time but in everyday practice we can get away with matter attracts matter and things are pulled towards the centre of the earth.

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3 hours ago, octave said:

This post comes with no guarantees but this is what I remember of this subject

What you remember is pretty close to the mark, especially your mentioning of inertia and tension on the string helps .


The whole thing is described by Newton's First Law of Motion states that every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force.  Let's start at the very beginning of our lead swinging.


We have an sphere whose mass is one kilogram. If we put it on the ground and leave it, the only force acting on it is Gravity, which acts along the radius drawn from the centre of Gravity of the Earth to the centre of Gravity of the sphere. In our frame of reference, we say that the vector of the force has a magnitude of 1 kg - down. If plotted on a 2D axis system, the force vector would be drawn from the point (0,0) along the negative Y-axis. There would be no vector component in the lateral direction. Since the acceleration due to gravity is 9.81m/sec^2, then the force acting on the sphere is 1 kg.m.sec^2, which is 1 Newton.


In order to move the sphere, we must apply a force to it to overcome the force of gravity. It is easy to realise that if we have to pick up the sphere, but what about moving it parallel to the ground? Let's put a string on the sphere and grab the other end of the string and try to pull the sphere toward us. Initially, the string will have the shape of a loop, but as we pull on it, the loop will become a straight line. The sphere won't be moving yet. Once the string is nice and straight from your hand to the sphere, you will start to feel the resistance of the sphere to moving. The force of the pull on the string is not sufficient as yet to overcome the force of gravity acting on the sphere. Eventually the pull is great enough and the sphere starts to move along the line described by the string (call it the shadow of the string) towards you.


Now, without increasing the strength of the force exerted by you on the string, begin to walk along the line of pull, away from the sphere. The sphere will increase its velocity parallel to the ground until it reaches the velocity you are walking at. The change in the velocity of the sphere is (VFinal - Vinitial). The change of velocity will take a measurable amount if time, t. The rate at which the velocity changed can be calculated from (VFinal - Vinitial)/t, which is acceleration.


SO, to get the sphere moving, you have applied a force of 1 kg x acceleration. If you keep walking at the same speed, you will have constant velocity, as will the sphere, until some outside force acts on you and the sphere. The simplest way that can happen is for you to either stop walking, or let go of the string, which is, in Physics, applying an equal force in the negative direction, stopping the sphere.


In the beginning, the stationary sphere will remain stationary due to its resistance to moving anywhere but towards the centre of the Earth. That's its inertia. The force applied to the string increases the tension between the ends of the string as the applied force tries to overcome the sphere's inertia by changing its velocity. At some point the  force on the string, which we feel as tension, will overcome the inertia of the sphere and the sphere will begin to gain velocity in the direction of the pulling force.


All this has been dealing with linear motion. The fun begins as we change the linear motion to circular motion.


 Enough for now. Next instalment will deal with Uniform Circular Motion.



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     " the only force acting on it is Gravity, which acts along the radius drawn from the centre of Gravity of the Earth to the centre of Gravity of the sphere."


or we will ALL be flat on the ground.

The Earth is spinning & that lets us stand upright.

sentreepugly that we don,t see it,s effects.Right.


Edited by spacesailor
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Sorry, Spacey, but both the Earth and you are spinning on its axis. and you are connected to the ground. So basically you are part of the earth. What is keeping you on your feet is the force created by your muscles to keep your vertical axis in line with a radius line to the centre of the Earth through which the acceleration due to gravity acts. That's why we like to lay down flat. It takes less energy.


Have a look at this: https://earthsky.org/earth/why-cant-we-feel-earths-spin



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The string and the sphere.


Consider what happens when we start pulling the sphere along with the string. We are exerting a force on the sphere to overcome its inertia. If we are all scientific about this, we would put a spring scale, or tensiometer between out hand and the sphere to measure the force of our pull.  We see the string straighten, and our hand feels a force where the string contacts it. That force we feel is due to the inertia of the sphere. It is the equal and opposite force to the one we apply by pulling the string. There's Newton's Third Law displayed. If we keep increasing the force of our pull, we will reach a point where the sphere just begins to move. That is the value of the inertia of the sphere. 


We know that the inertia of the sphere is equal to its mass times acceleration due to gravity (m.g) which we know for a 1 kg mass is 9.81 Newtons. If we pull on the string with a measured force of 9.81 Newtons, we have a balance of forces, and nothing moves. What happens when we drop the string? Do we fall away from the sphere, or does it move away from us? No. We both remain where we are due to our individual inertias. All we have done is stopped exerting equal and opposite forces on each other. There is not other source of a force to move either of us.


This concept of the pulling force equalling the inertia of the sphere is the crux of the proof that, although our senses seem to react to to something that would move the sphere away from us, that something is imaginary.


Now I am going to prepare some stuff to explain uniform circular motion. Be back in a while.



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OME your last post made me think and I still believe in centrifugal force.

What happens if instead of a string you have a solid member between your finger and twirl away.

The centripetal force stops the weight from moving further away and a non existent force tends to make it move away. Everything is in equilibreum.

Now quickly raise your finger a metre and what forces are there?

Which leads to the propeller whirling round. Twist its axis and there is another force moving it in another direction.

I don't understand it, or I could say "It sucks" but the pedants say sucking doesn't happen, it is just a blow in another direction.

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1 hour ago, Yenn said:

What happens if instead of a string you have a solid member between your finger and twirl away.

You mean like this? The Scottish origin of hammer throwing


1 hour ago, Yenn said:

Now quickly raise your finger a metre and what forces are there?

 evolved from its early informal origins to become part of the Scottish Highland games in the late 18th century, where the original version of the event is still contested today.


1 hour ago, Yenn said:

quickly raise your finger a metre and what forces are there

I'll explain this later tonight. It takes a while and I've got some chores to do before I get back on the computer.

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8 hours ago, Yenn said:

The centripetal force stops the weight from moving further away and a non existent force tends to make it move away. Everything is in equilibrium.

Before I go into the algebra of the vector analysis, watch this video on throwing the hammer for the practical application of the ball on a string.





Watch how the boys' arms straighten as they begin to get the ball moving on a circular path. That is the result of the centripetal force the boys are exerting on the ball. Notice how as the ball goes faster they tend to lean away from it, using their backs to increase the tension.


Notice, too, the "gate" they are throwing through. The left hand gate must be open for throwers rotating anti-clockwise. The right hand gate must be open for throwers turning clockwise. The shot will be a foul if the hammer falls out of a 40° sector marked on the field from the centre of the circle, that is, 20 degrees either side of a line drawn down field from the centre of the circle.



Also, the hammer thrower is trying to get as much distance as possible. That's why the path of the ball rises in front of the thrower and swings down behind. The aim is to release the hammer as close to 45 degree upwards as possible because that gives the longest ballistic flight of the ball.


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I can understand on an absolutist level why you're trying to debunk it, as a standalone force it doesn't exist.


But any object which is in motion and has a force applied to turn it is going to want to continue travelling in a straight line (Newton's first law), and this will result in a pull to the opposite side to the turn.  Simple.  This is why planes (and bikes and motorbikes and boats) bank into a turn,  and why you'll feel yourself getting heavier as it does.  Or in a car you'll just slide towards the outside.

Now we don't have to call this motion anything, but it's simpler if we do, so as a centrifuge forces things to the outside - why not call it centrifugal force?

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I think that we can look at things in more than one way.   Everybody knows that things fall to the ground and we call that gravity.  We think it is because matter attracts matter and in practice that works in everyday life but a physicist will bang on about mass curving space time.   For their purposes this is more correct and allows them to make calculations that are important to their work.  



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1 hour ago, Marty_d said:

any object which is in motion and has a force applied to turn it is going to want to continue travelling in a straight line (Newton's first law)

Quite correct.


The point is that the "straight line" is located at 90 degrees to the force. I have shown that the force being applied to the mass is the tension between, say, the swinger's body and the mass. I showed this by describing how, if you put the mass on a surface, then pulled on the connecting string - that is increased the force of tension between yourself and the mass, you would overcome the inertia (weight) of the mass and it would start coming towards you. If the tension applied was just equal to the weight of the object, as soon as you released the tension, that is applying a force to change the velocity of the mass, the mass would stop moving. In practical terms, if the tension was greater than the weight and the mass started to move, once the tension was released other forces, mostly friction would stop it. In any case, once the tension was released, the mass would not move in the opposite direction - away from the body.


That's all one part of the movement in a circular path. The next part is getting the mass to move in a circular path. 


Let's start with something like the mass held in the hands against the chest, with nothing to restrict its movement. If the mass is thrown away from the chest it will follow a horizontal path (while it is falling vertically). That shows that a body in motion will travel in a straight line. Now let's attach the string and start swinging the mass in an anticlockwise direction (for right-handed people) . At the first instant, the mass will move in a straight line at . However, it will immediately be acted upon by the force of tension that is pulling it towards your body. That force will change the line of flight to the left. An infinitely short time later the mass will travel in that new direction, but still at 90 degrees to the tension force in the string. If you keep swinging the mass, it will eventually come around over the starting point.


We have to differentiates between two terms. First we have "Speed". Speed is called a "scalar" value. Scalar values simply have magnitude - length and time are two scalar values. Secondly we have "Velocity", which is a vector value. Vectors are a scalar value in a stated direction, eg "60 kph west", or more correctly, 60 kph 270 degrees. During a revolution, the scalar value of the mass's velocity does not change, but its vector value does because of the constant change in direction. The white lines on this image represent the velocity vectors at the ends of the spokes. 



If that was our mass on a string, or maybe an overhead view of a merry-go-round, if the force pulling the mass towards the centre (Tension) suddenly ceased to act on the mass, the mass would continue along the straight line vector that existed at the instant the force was removed. Go back and watch the video of the boys throwing the hammer and see that the hammer travels in a straight line after release, and it is released so that the velocity vector is pointing into the scoring area in front. 


Enough for now. More later.

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Try the first part of the experiment yourself. Tie a string around something with a bit of weight. Have the string loose, then start pulling on it until the string straightens out. That's you putting tension on the string. If you keep pulling, you will gently start moving the weight towards you. That means the tensional force you are applying to the weight is overcoming its inertia which is what makes it stay on the ground where you first put it. Now, drop the string. The tension force is gone and the weight stops moving. It doesn't move in the opposite direction to that which you were pulling it.


Don't worry about which direction the weight would fly off because I haven't got to that part yet. I will after dinner tonight.


Just a hint, it has to do with the momentum of the weight.



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This discussion is becoming the same as the "Does God exist?" discussion - a question of Fact or Faith.


It has been my approach to the question, "Is Centrifugal Force real?" to apply the Scientific Method. The scientific method is an iterative, cyclical process through which information is continually revised. The method involves eight steps:

  1. Define a question
  2. Gather information and resources (observe)
  3. Form an explanatory hypothesis
  4. Test the hypothesis by performing an experiment and collecting data in a reproducible manner
  5. Analyse the data
  6. Interpret the data and draw conclusions 
  7. Publish results
  8. Retest 

Admittedly, I have used examples and the results of others to present observations and analyse the information, and I have presented an interpretation of the data. However, no one who holds the counter view that Centrifugal Force exists has provided any stronger rebuttal than what might be a description of a feeling in the gut. They have jumped from Step 3 to Step 7 without the important intervening steps.


I can understand how Galileo felt when his  championing of heliocentrism and Copernicanism met with opposition from within the Catholic Church and from some astronomers. The matter was investigated by the Roman Inquisition in 1615, which concluded that heliocentrism was "foolish and absurd in philosophy, and formally heretical since it explicitly contradicts in many places the sense of Holy Scripture".


I hold that what I have written is Fact, and can only issue the same challenge a Christ is reported to have issued in John 8:7 " He that is without sin among you, let him first cast a stone".






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