Acceleration of clubhead

[Jim Kobylinski]

Jim, in a nutshell, we really don't know how to explain the intrinsic nature of inertial force. Let's just simply accept that it is there. It is indeed very real in its multiple manisfestations. If I find an explanation I am afraid that I will not post it on this forum -a potential Nobel Prize idea merits a different type of forum.

This was exactly the point of my question. I was kind of bating the other people (not you). I am starting to understand that because we are creating a force inward towards a center there is another force acting on the band (even if we didn't have a golf ball attached to it) trying to make it flee the center and thus it becomes longer and longer. So there has to be SOMETHING doing it and it surely isn't fictious.

 

[mandrin]

This was exactly the point of my question. I was kind of bating the other people (not you). I am starting to understand that because we are creating a force inward towards a center there is another force acting on the band (even if we didn't have a golf ball attached to it) trying to make it flee the center and thus it becomes longer and longer. So there has to be SOMETHING doing it and it surely isn't fictious.

Jim,

Is it not bizarre that considering this simple problem where one can easily visualize and actually measure very readily the outward going force on the elastic band that so many scientists and text books keep referring to centrifugal as being a fictitious force?

Centrifugal force can indeed be a fictitious force but only in a rotating reference frame but that is of no concern to a golfer. To my knowledge nobody has yet played a real golf game inside a rotating frame.

It is simply a matter, in one’s mind, to see the mass and the elastic band separately and consider the force operating on each. The mass has one inward force acting on it which keeps it in the orbit and is furrnished by the elastic band.

And the elastic band has one equal but outward going inertial force acting on it stretching it hence furnishing the inward force for the mass. But the two forces, even being equal and opposing, do not cancel, as they don’t act on the same object.

At least we are now two to understand this matter perfectly.

I am sorry not being the fish you were bating but I hope it will do nevertheless.

 

[tongzilla]

But the two forces, even being equal and opposing, do not cancel, as they don’t act on the same object.

mandrin, can you please explain this a bit more? thx

 

[Burner]

mandrin, can you please explain this a bit more? thx

Mandrin,

Can you also give us any examples of the presence of Centrifugal force in the absence of a real Centripetal Force?

 

[Bronco Billy]

Mandrin,

Can you also give us any examples of the presence of Centrifugal force in the absence of a real Centripetal Force?

Hi There

Forces are Like Socks.....

Cheers

 

[mandrin]

mandrin, can you please explain this a bit more? thx

tongzilla,

Let’s look at a particular logic mistakes made be quite a few people. It might help to size the problem better.

The argument is made that if centrifugal force existed than, if the elastic band is cut, the mass should move radially due to this centrifugal force and not tangentially as it actually does.

There are two fundamental errors implicit in this type of argument.

- It assumes that the point of application for the centrifugal force is acting on the mass instead of on the elastic band.

This argument leads to a nonsensical conclusion. If implies that both centrifugal and centripetal force are acting simultaneously on the mass. However than they cancel each other - no motion is therefore possible, whatsoever, for the mass.

- It ignores the fact that both centrifugal and centripetal force only exist when the restraint is present. Cut the restraint and instantaneously there is no force left whatsoever.


Another type of error frequently seen:

- ‘The object at the end of the string feels the centripetal force, the center feels the centrifugal force, but this centrifugal force is not a REAL force it is mearly the result of a centripetal force'.

It is really sad that this kind of nonsense is repeated everywhere. It completely contradicts Newton’s Third Law. Action and reaction forces are both real.

Moreover it says in one single phrase that the center does feel a centrifugal force but yet it isn't real. It is or it is not, can’t have it both ways, at the same time.

 

[neil]

Jim,

Is it not bizarre that considering this simple problem where one can easily visualize and actually measure very readily the outward going force on the elastic band that so many scientists and text books keep referring to centrifugal as being a fictitious force?

Centrifugal force can indeed be a fictitious force but only in a rotating reference frame but that is of no concern to a golfer. To my knowledge nobody has yet played a real golf game inside a rotating frame.

It is simply a matter, in one’s mind, to see the mass and the elastic band separately and consider the force operating on each. The mass has one inward force acting on it which keeps it in the orbit and is furrnished by the elastic band.

And the elastic band has one equal but outward going inertial force acting on it stretching it hence furnishing the inward force for the mass. But the two forces, even being equal and opposing, do not cancel, as they don’t act on the same object.

At least we are now two to understand this matter perfectly.

I am sorry not being the fish you were bating but I hope it will do nevertheless.

I was taught (long time ago)that centrifugal force was only relevant in the rotating frame-and therefore was only applicable to objects within that frame.
In all other applications ,the common (everyday )term was centrifugal, but scientifically, was actually centripetal.
I'm not into this argument ,as it is a p@#$ing contest on science -on a golf forum (?).
For what it's worth -does it matter? -as long as we all talk the same language.Which is what Mr Kelly tried to do in his book.
MR.MANZELLA -please spare us -your passion for your trade cannot extend into tolerance of references to "Baiting" 'surely?

 

[mandrin]

Mandrin,

Can you also give us any examples of the presence of Centrifugal force in the absence of a real Centripetal Force?

Burner,

If a bead can move without friction along a rod which rotates around a center it experiences centrifugal force without centripetal force being present.

 

[JeffM]

Mandrin

I don't understand your latest comment. What is getting the bead to move in the first place? Surely it is subjected to a force that has a centripetal element if the rod turns around a central axis? As the rod starts to turn, a force must be transmitted to the stationary bead, and that force is not linear because the rod immediately underneath the bead is moving in a circular path, and NOT a straight line path.

Jeff.

 

[puttmad]

...

Hi There

Forces are Like Socks.....

Cheers

What? So you start with a matching pair and then when you wash them you end up with only one?.....

 

[mandrin]

Mandrin

I don't understand your latest comment. What is getting the bead to move in the first place? Surely it is subjected to a force that has a centripetal element if the rod turns around a central axis? As the rod starts to turn, a force must be transmitted to the stationary bead, and that force is not linear because the rod immediately underneath the bead is moving in a circular path, and NOT a straight line path.

Jeff.

JeffMan,

Initial condition - the bead starts with a small veloctity at t = 0.

 

[JeffM]

Mandrin

Then doesn't simple physics apply. The force moving the rod is circular, and therfore the line of force acting on the bead is at right angles to the radius of the circle. The bead is subjected to this tangential force, but it can only travel sideways, along the longitudanal axis of the rod, even though the force acting on the bead is not primarily directed in that direction. Therefore, the bead is not moving in response to a centrifugal force - which would be directed along the longitudanal axis of the rod, away from the centre. It is moving in that direction because it is constrained by the nature of its attachment to the rod to move along the longitudanal axis of the rod - either towards the center, or away from the center.

Jeff.

 

[nmgolfer]

This is a fine example of how people (including some scientists) are confused about centrifugal force... even in inertial coordinate systems. But make no mistake... simple physics does apply...

The only force the bead experiences is that which is transmitted to it via the rod. There is no centrifugal (or centripetal) force acting on the bead. Since there is no centripetal force present, the bead "experiences" the rod sliding through it.

There is a centrifugal force present in the system as described however. The hub and axle of the rod feels a tug ... that is assuming the rotating rod is not massless. That's centrifugal force i.e. the reaction to the mass of the rod times its centripetal acceleration: w^2/r.

If the bead were to remain stationary on the rod (and not slide off) a centripetal (center seeking force) must be provided. This is known as the "centripetal force requirement". Since it is not, the bead eventually slides off... but NOT due to "centrifugal force".

Imagine you have a ball sitting on the seat of your car. You hit the breaks and the ball rolls off the seat. Mandrin et al would have you (mistakenly) believe centrifugal force acted on the ball causing it to roll off the seat. But that's not what happened at all. What really happened brakes on the wheels of the car caused the seat to slow down underneath the ball. The ball's inertia makes it want keep it moving and since there's no force acting on it... it does keep moving.

Invoking "centrifugal force" to explain why a bead slides off a rod or a ball rolls off the car seat or why a golf club releases is a cop-out . Its a convenient, easy (for most) to understand, yet completely wrong explanation. Its not unlike (most) teachers claiming Bernoulli's equation explains lift on an airplane wing.... its ubiquitous and its patently wrong.

 

[daniell]

nmgolfer,

The force exerted on the bead by the rotating rod is tangential, is it not? But why does the bead slide out along the rod?

cheers,

daniel

 

[daniell]

Nmgolfer said .. "Imagine you have a ball sitting on the seat of your car. You hit the breaks and the ball rolls off the seat. Mandrin et al would have you (mistakenly) believe centrifugal force acted on the ball causing it to roll off the seat."

Bad example, when you hit the brakes, the ball's inertia causes it to continue to move and thus rolls off the seat. As there is no rotation, there is of course no centrfugal force. I'm sure Mandrin would agree with this explanation.

cheers,

daniel

 

[daniell]

Let me elaborate on my post #195 above and relating it to the bead example.

Let us take an instantaneous moment. Basically, the rod exerts a force (tangential to the rod) on the bead. As the rod continues to rotate, we can witness the bead sliding out of course. What nmgolfer is saying is that due to inertia, the beads wants to continue to move in a straight line and that this causes the bead to slide out of the rod. This is not wrong.

However, if you take a rotating frame, the bead IS sliding out of the rod. As the force that the rod exerts on the bead is always tangential, there appears to be a force horizontal to the rod that is pushing the bead out. This force is what science classify as centrifugal force.

Please relate this to the explanantion and example from http://phun.physics.virginia.edu/topics/centrifugal.html:

++
Centrfugal Force

An object traveling in a circle behaves as if it is experiencing an outward force. This force, known as the centrifugal force, depends on the mass of the object, the speed of rotation, and the distance from the center. The more massive the object, the greater the force; the greater the speed of the object, the greater the force; and the greater the distance from the center, the greater the force.

It is important to note that the centrifugal force does not actually exist. We feel it, because we are in a non-inertial coordinate system. Nevertheless, it appears quite real to the object being rotated. This is because the object believes that it is in a non-accelerating situation, when in fact it is not. For instance, a child on a merry-go-round is not experiencing any real force outward, but he/she must exert a force to keep from flying off the merry-go-round. Because the centrifugal force appears so real, it is often very useful to use as if it were real. The more massive the object, the greater the force. We know that this is true because an adult will have a harder time staying on a merry-go-round than a child will. The greater the speed of rotation, the greater the outward force. We know that this is true because a merry-go-round is harder to stay on, the faster it rotates. If you move further out on the merry-go-round, you will have to exert a greater force to stay on. In order to stay on a circular path, we must exert a force towards the center called centripetal (or "center-seeking") force. Consider a rope with a ball on the end. You can swirl the ball around in a circle over your head while holding onto the rope. The ball experiences the so-called centrifugal force, and it is the rope that provides the force to keep in moving in the circle.
++

cheers,

daniel

 

[mandrin]

Mandrin

Then doesn't simple physics apply. The force moving the rod is circular, and therfore the line of force acting on the bead is at right angles to the radius of the circle. The bead is subjected to this tangential force, but it can only travel sideways, along the longitudanal axis of the rod, even though the force acting on the bead is not primarily directed in that direction. Therefore, the bead is not moving in response to a centrifugal force - which would be directed along the longitudanal axis of the rod, away from the centre. It is moving in that direction because it is constrained by the nature of its attachment to the rod to move along the longitudanal axis of the rod - either towards the center, or away from the center.

Jeff.

JeffMann,

“Then doesn't simple physics apply.” - Correct. Nothing outlandish. Basic dynamics.

“The force moving the rod is circular, and therfore the line of force acting on the bead is at right angles to the radius of the circle.” - Correct

“The bead is subjected to this tangential force, but it can only travel sideways, along the longitudanal axis of the rod, even though the force acting on the bead is not primarily directed in that direction.” - Correct

“Therefore, the bead is not moving in response to a centrifugal force - which would be directed along the longitudanal axis of the rod, away from the centre.” - Incorrect.

“It is moving in that direction because it is constrained by the nature of its attachment to the rod to move along the longitudanal axis of the rod - either towards the center, or away from the center.” - A mass only accelerates when a force is acting on it. The mass accelerates along the rod hence a force is acting on it.

Instead of talking about the ‘nature of attachments’ let’s use mathematics to show the existence of the centrifuagl force and determine its magnitude. Have a look here .

 

[JeffM]

Mandrin - Unfortunately, I do not have the brain power to understand your mathematical explanation. I need simple child-like explanations. You seem to have an arrow F through the bead implying that the acting force is at right angles to the rod. However, I cannot understand that point. If there is a circular torque force acting on the rod, thus causing it to move in a circle, then that force must be circular in direction. I can imagine dividing that circular force into two component forces - a force at right angles to the rod (equivalent to a force that is tangential to the circle that the bead would be following if it didn't change its position along the rod) and another force that is more centrally directed (what some people would regard as being centripetally-directed). Now, if the bead is stationary, and thereby having a property of inertia, it would resist any movement. I can then imagine the rod sliding INWARDS away from the bead - due to the centripetal-force component of the circular torque force moving the rod. However, the rod cannot slide inwards because it is fixed at the center - therefore the bead must slide OUTWARDS. If you call that force, causing the bead to move outwards, a centrifugal force, then surely its existence is due to the fact that the rod is moving along a circular path, and not a straight line path. If the rod was not fixed at the centre, and a force, acting at right angles to the longitudanal axis of the rod, moved the rod along a straight line path - the bead would not move. The bead moves OUTWARDS because the force moving the rod has a circular path, and the change in direction from a straight line path to a circular path implies a centripetal (centrally-directed) force component.

Jeff.

 

[Bronco Billy]

Instead of talking about the ‘nature of attachments’ let’s use mathematics to show the existence of the centrifuagl force and determine its magnitude. Have a look here .[/QUOTE]

Hi There

WOW Very Convincing..............

Cheers

 

[mandrin]

Mandrin - Unfortunately, I do not have the brain power to understand your mathematical explanation. I need simple child-like explanations. You seem to have an arrow F through the bead implying that the acting force is at right angles to the rod. However, I cannot understand that point. If there is a circular torque force acting on the rod, thus causing it to move in a circle, then that force must be circular in direction. I can imagine dividing that circular force into two component forces - a force at right angles to the rod (equivalent to a force that is tangential to the circle that the bead would be following if it didn't change its position along the rod) and another force that is more centrally directed (what some people would regard as being centripetally-directed). Now, if the bead is stationary, and thereby having a property of inertia, it would resist any movement. I can then imagine the rod sliding INWARDS away from the bead - due to the centripetal-force component of the circular torque force moving the rod. However, the rod cannot slide inwards because it is fixed at the center - therefore the bead must slide OUTWARDS. If you call that force, causing the bead to move outwards, a centrifugal force, then surely its existence is due to the fact that the rod is moving along a circular path, and not a straight line path. If the rod was not fixed at the centre, and a force, acting at right angles to the longitudanal axis of the rod, moved the rod along a straight line path - the bead would not move. The bead moves OUTWARDS because the force moving the rod has a circular path, and the change in direction from a straight line path to a circular path implies a centripetal (centrally-directed) force component.

Jeff.

Jeffmann,

Just try simple physics instead of complicated reasoning.

A mass only accelerates when a force is acting on it.

The bead is accelerating outwards.

Hence a force is acting on it.

That’s it, that’s all.

Amen