The magic of science

[mandrin]

Everyone is so busy with serious golf business that it is time to lighten up the atmosphere a bit with a magician's trick which really is no trick but a mismatch between science and intuition. It concerns centrifugal force, this inertial force seemingly not existing for some but really joyfully bursting with activity and readily measured with simple equipment.

Since a golf swing is basically rotational in nature the basic inertial forces acting are centripetal and centrifugal like forces. Centripetal and centrifugal forces are however, strictly speaking, defined as 'central forces', i.e., forces that emanate or terminate from a stationary center and whose line of action hence passes through this center.

In a golf swing however there are multiple centers of rotation which moreover are not fixed in space/time. Therefore care has to be exercise when imposing the very simply image of a whirling mass as being representative for a golf swing. For instance, is there a stationary center of rotation for the clubhead? Should it be defined by its instantaneous trajectory or maybe by some physical location on the golfer?

 

[Slicey McDuff]

I tried it, and much to my son's horror (his watch) it works, COOL!!!!

 

[Jim Kobylinski]

very neat "trick"

 

[JonWil]

Mandrin,
Can these forces be completely overcome by the use of muscle in a conventional golf swing? Or are they always derived, and giving influence, given the instrument used and the typical form?

 

[jake2]

Everyone is so busy with serious golf business that it is time to lighten up the atmosphere a bit with a magician's trick which really is no trick but a mismatch between science and intuition. It concerns centrifugal force, this inertial force seemingly not existing for some but really joyfully bursting with activity and readily measured with simple equipment.

Since a golf swing is basically rotational in nature the basic inertial forces acting are centripetal and centrifugal like forces. Centripetal and centrifugal forces are however, strictly speaking, defined as 'central forces', i.e., forces that emanate or terminate from a stationary center and whose line of action hence passes through this center.

In a golf swing however there are multiple centers of rotation which moreover are not fixed in space/time. Therefore care has to be exercise when imposing the very simply image of a whirling mass as being representative for a golf swing. For instance, is there a stationary center of rotation for the clubhead? Should it be defined by its instantaneous trajectory or maybe by some physical location on the golfer?

Nice illustration of what's happening. I can see some analogy to the golf swing where the 3ball gravity pull does much of the work for accelerating 1ball. Then past low point it goes to reverse, like club pulling body to the finish.

It also illustrates how shortening swing radius can play part in the kinetic chain.This is an example of efficient kinetic chain, where nothing needs to stop suddenly to transfer kinetic energy. Still 3ball certainly starts to slow down much before low point even when gravity keeps on pulling.


One thing I wish though is that you could find a way of explaining centripetal force without having to resort to the virtual centrifugal force. Even if it probably makes no difference to most people.

Force is required to change velocity, be it it's magnitude or direction. Velocity is a vector.

People do not usually have problem in accepting that when you change it's magnitude (accelerate or decelerate) a force is required and there is no need to explain this by some kind of virtual force that the mass generates to resist the change of velocity.

However, when we change the direction of the velocity and force is again required, this time it is not understood the same way and we need to resort to a centrifugal force as being the cause of the pulling force felt. On a circular path the direction is continuously changing needing continuous pulling force.

Just my thoughts on the subject...

 

[mandrin]

Mandrin,
Can these forces be completely overcome by the use of muscle in a conventional golf swing? Or are they always derived, and giving influence, given the instrument used and the typical form?

JonWil,

Try to maintain fully the angle -no release at all - swinging a driver at full speed. Report back when you have tried this simple experiment.

 

[mandrin]

jake2,

Thanks for your comments. Hope you don't mind when I have a few reservations about several of your comments.

'I can see some analogy to the golf swing where the 3ball gravity pull does much of the work for accelerating 1ball. Then past low point it goes to reverse, like club pulling body to the finish.'

The analogy only goes so far. In a real golf swing gravity plays a minor role.

'It also illustrates how shortening swing radius can play part in the kinetic chain. This is an example of efficient kinetic chain, where nothing needs to stop suddenly to transfer kinetic energy. Still 3ball certainly starts to slow down much before low point even when gravity keeps on pulling. '

I would not really call it a kinetic chain. Rather an ensemble of two point masses sharing the same constant total energy continuously exchanging their potential and kinetic energies. The 3ball mass not only slows down but does it rather rapidly and comes to a complete stop when reversing direction. At that precise moment it has surrendered ALL its kinetic energy to the 1ball mass.

'One thing I wish though is that you could find a way of explaining centripetal force without having to resort to the virtual centrifugal force. Even if it probably makes no difference to most people.'

I am not really explaining centripetal force. Moreover centrifugal force is not a virtual force. It is here the dominant real force acting on the 3ball mass. These two real forces are a siamese twin as follows from Newton's 3d law.

'People do not usually have problem in accepting that when you change it's magnitude (accelerate or decelerate) a force is required and there is no need to explain this by some kind of virtual force that the mass generates to resist the change of velocity.'

When a heavy brick brakes loose from a wall and just happens to hit you on the head would you, bleeding and staggering around, feel that it is only imaginary and due to some kind of esoteric virtual force that the brick generates to resist change in its velocity?

'However, when we change the direction of the velocity and force is again required, this time it is not understood the same way and we need to resort to a centrifugal force as being the cause of the pulling force felt. On a circular path the direction is continuously changing needing continuous pulling force.'

Rotational mechanics is indeed not readily accessible to our intuitive understanding but we have fortunately mathematics to help our failing intuition. Fig1 shows clearly that one can't escape the simple obvious fact that it is the centrifugal force acting through the cord on the 3ball mass. In this particular case gravity is the only external force acting on the system and both centripetal and centrifugal force are inertial reaction forces only coming into existence when motion occurs due to gravity.

 

[jake2]

It is quite surprising but there are still many who simply discard centrifugal force from the outset as some form of fictitious force - considering it to be some form of magician's tricks somehow required to balance things in science. However in our experiment it obviously exists and moreover is also readily measured. Just insert a small fish tension scale just above the '3ball mass'. As shown below in Fig4 the force exerted on the 3ball mass is primarily due to the centrifugal force exerted on the cord by the rotating 1ball mass.

Would you also saying that a car accelerating exerts a backward force to the road. Because with the right setup, you could also measure this force. Section of the road surface would have to be on rollers and tension scale in one end.
You could ten say that the acceleration is primarily due to this force exerted to the road. It's a real force because you can measure it, right? So is the road pushing the car?

Your example is more complex because both masses are moving and there has to be transfer of momentum and kinetic energy between the masses.

 

[mandrin]

Would you also saying that a car accelerating exerts a backward force to the road. Because with the right setup, you could also measure this force. Section of the road surface would have to be on rollers and tension scale in one end.
You could ten say that the acceleration is primarily due to this force exerted to the road. It's a real force because you can measure it, right? So is the road pushing the car?

Your example is more complex because both masses are moving and there has to be transfer of momentum and kinetic energy between the masses.

jake2,

I am not really inventing anything new or special. We are dealing here with basic physics. Forces always occur in equal and opposite pairs. If object A exerts a force on object B, an equal but opposite force is exerted by object B on object A. Newton's 3d law.

 

[jake2]

jake2,
I am not really inventing anything new or special. We are dealing here with basic physics. Forces always occur in equal and opposite pairs. If object A exerts a force on object B, an equal but opposite force is exerted by object B on object A. Newton's 3d law.

Fair enough, I do not dispute that for any action there's always an equal opposite reaction.

I just see the centrifugal force purely as a reaction.

I just can't see how centrifugal force could do any work for you in a golf swing or anywhere else. You have to do the work with gravity helping slightly.

And it's a question of how to do it efficiently.

 

[jake2]

jake2,
I would not really call it a kinetic chain. Rather an ensemble of two point masses sharing the same constant total energy continuously exchanging their potential and kinetic energies. The 3ball mass not only slows down but does it rather rapidly and comes to a complete stop when reversing direction. At that precise moment it has surrendered ALL its kinetic energy to the 1ball mass.

The interesting part for me in this is how the transfer of kinetic energy actually happens.
Isn't shortening swing radius of 1ball must be the main reason?
Could some of it apply to a real golf swing, since the shortening of radius does seem to happen there too?
I do not believe your presenting this just to try to prove existence of centrifugal force.

 

[JonWil]

JonWil,

Try to maintain fully the angle -no release at all - swinging a driver at full speed. Report back when you have tried this simple experiment.

Mandrin,

Conquered by the forces.... couldn't hold the angle.
Guess I'm a wimp.

 

[mandrin]

Mandrin,

Conquered by the forces.... couldn't hold the angle.
Guess I'm a wimp.

JonWil,

No need to feel like a wimp. A friend of the late Prof Jorgensen, author of "The Physics of Golf", who was told about the large torque developing in the down swing managed to snap the shaft maintaining the angle.

 

[mandrin]

Fair enough, I do not dispute that for any action there's always an equal opposite reaction.

I just see the centrifugal force purely as a reaction.

I just can't see how centrifugal force could do any work for you in a golf swing or anywhere else. You have to do the work with gravity helping slightly.

And it's a question of how to do it efficiently.

jake2,

I realize that centrifugal force is being treated frequently as if it is some infectious disease to be avoided at all cost. Let's however simply use common sense.

I simply invite you to look carefully at Fig1.

What are the forces acting on the 3ball mass?

Gravity. Fine, but what else?

Agreed, there seems to be indeed another force pulling the 3ball mass upwards against gravity.

Where is this force coming from?

 

[mandrin]

The interesting part for me in this is how the transfer of kinetic energy actually happens.
Isn't shortening swing radius of 1ball must be the main reason?
Could some of it apply to a real golf swing, since the shortening of radius does seem to happen there too?
I do not believe your presenting this just to try to prove existence of centrifugal force.

"The interesting part for me in this is how the transfer of kinetic energy actually happens."

If I drop a mass its potential energy is converted into kinetic energy of motion. In our case we have a more complicated 'pas de deux' implying two masses both falling due to gravity converting their potential energy into kinetic energy all the while 'sharing, exchanging and communicating' via the cord. Due to its nifty angular motion, and ensuing centrifugal force, the1ball mass temporarily manages to let the 3ball mas escape the gravitational pull of the earth for a little while.

"Isn't shortening swing radius of 1ball must be the main reason?"

The primary cause for motion here is gravity. Once motion occurs inertial forces of motion come into play. These inertial forces interact via the cord affecting the relative motions of the two masses and this leads to changes in their respective kinetic energy of motion.

" Could some of it apply to a real golf swing, since the shortening of radius does seem to happen there too?"

When thinking in terms of a golf swing another reasoning applies. Here one can try to deliberately change the radius of motion hence being at cause. In general shortening the swing radius results in a velocity increase at the periphery.

"I do not believe your presenting this just to try to prove existence of centrifugal force."

Primarily, but I also like to point out things of possible interest. One can look at the golf swing as being a kinetic chain. Yet a very different perspective is obtained looking at the swing as being one having a changing radius.

 

[jake2]

"I do not believe your presenting this just to try to prove existence of centrifugal force."

Primarily, but I also like to point out things of possible interest. One can look at the golf swing as being a kinetic chain. Yet a very different perspective is obtained looking at the swing as being one having a changing radius.

Could it be that it's a kinetic chain with changing radius playing a part in it.

As I've tired to refresh my knowledge on physics, I've realized that it's pointless to argue if centrifugal force exists on not, because it depends on your frame of reference. I've been looking at it from inertial reference frame when Mandrin's using rotational (non-inertial) reference frame.

There's a pretty good explanation at:
Fictitious force - Wikipedia, the free encyclopedia

 

[mandrin]

As I've tired to refresh my knowledge on physics, I've realized that it's pointless to argue if centrifugal force exists on not, because it depends on your frame of reference. I've been looking at it from inertial reference frame when Mandrin's using rotational (non-inertial) reference frame.

There's a pretty good explanation at:
Fictitious force - Wikipedia, the free encyclopedia

jake2,

I have not used any rotational reference frame.
My reference frame is simply mother earth.
I proposed before to use common sense.
I hence simply repeat the invitation -

what is your response, no 'Googling', to my simple questioning below?

jake2,

I realize that centrifugal force is being treated frequently as if it is some infectious disease to be avoided at all cost. Let's however simply use common sense.

I simply invite you to look carefully at Fig1.

What are the forces acting on the 3ball mass?

Gravity. Fine, but what else?

Agreed, there seems to be indeed another force pulling the 3ball mass upwards against gravity.

Where is this force coming from?

 

[birdie_man]

That match trick is a real mind-mangler. (mind-scrambler) Really.

I have built the whole scenario in my mind and cannot understand why the match end would react like that.

 

[mandrin]

That match trick is a real mind-mangler. (mind-scrambler) Really.

I have built the whole scenario in my mind and cannot understand why the match end would react like that.

Interesting magic trick as it is based on science yet appears to be magic.

However you can readily destroy the magic when doing the trick yourself.

 

[jake2]

jake2,
I realize that centrifugal force is being treated frequently as if it is some infectious disease to be avoided at all cost. Let's however simply use common sense.

I simply invite you to look carefully at Fig1.

What are the forces acting on the 3ball mass?

Gravity. Fine, but what else?

Agreed, there seems to be indeed another force pulling the 3ball mass upwards against gravity.

Where is this force coming from?

Centripetal acceleration of the 1ball or centrifugal force of the 1ball depending on the frame of reference.

Centripetal acceleration (centrifugal force) increases as 1ball velocity increases and radius of rotation decreases. The interesting part of it to me is how this combination works rapidly accelerating as it is able to draw kinetic energy from 3ball.

I must admit that centrifugal force may be more understandable to most people (making more common sense) than thinking in terms of centripetal acceleration.

What comes to googling, I also admit that have to resort to it sometimes, since I do not yet know everything. And I might even sometimes change my opinion when I learn something new.

Anyway I'm still on the opinion that use of centrifugal force is not necessary in physics, but I will not object to the use of it anymore.