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Post by imperfectgolfer on Mar 2, 2010 22:06:09 GMT -5
Many golfers do not believe that there is such a thing as a centrifugal force (CF force) although they often believe that there is such a thing as a centripetal force (CP force). I cannot understand that viewpoint, so I have created a model to demonstrate the presence and power of a CF. Imagine a model disc system, about 3 feet in diameter, consisting of two 3 feet round disc-plastic plates that are joined together at the rim (circumference) by a round metal band that is ~1" in width, so that there is a space of about 1" between the two round plastic discs. Imagine that a central axle goes through the center of the two discs, and that the axle can be rotated clockwise causing the entire disc system to spin horizontally (see side-view diagram below) because it is firmly attached to the two plastic discs. Imagine that there are 4 channels built into the peripheral section of the disc system, so that each channel has a length of 12" and a width of 1" and that the sides of the channel are parallel (not drawn perfectly parallel in the diagram). Imagine that there is a hexagonal-shaped metal slug within each channel so that each metal slug can freely slide up-and-down the channel. Imagine that there is a metal spring in channel A that attaches the central end of the metal slug to the central end of that A channel (at point x). Now imagine the entire disc system spinning clockwise (horizontal to the ground) at a finite speed. I believe that the metal slugs will slide to the peripheral end of the channel and end up at point Y due to a CF force that comes into "existence" when the two discs spin in a circular manner around a central axis. The metal slug in channel A is restrained by the metal spring and it will not slide to the end of the channel, and it will end up at point Z (intermediate between point X and point Y). Point Z's distance from point X is dependent on the strength of the CF force relative to the tensile strength/stretchability of the spring. When looked at from above, if the metal slug (at point Z) remains a fixed distance from point X, then it can be conceived to be orbiting in space in a state of balance (where CP force = CF force). The magnitude of the CF force, and therefore the CP force, can be measured by the spring's change in length from its resting state to its state at position Z (if its tensile strength/stretchability characteristics are known). If the two discs are spun at a faster speed, then it will increase the magnitude of the CF force. The degree of change in magnitude of the CF force will be reflected by the degree point Z moves away from point X. At that time point, the metal slug at point Z will be creating a larger radius orbit, but the CF force will still be equal to the CP force if point Z remains a "certain fixed" distance from point X. This situation fits in with Netwton's third law of physics - that states that every force must have a balancing force of equal magnitude if a moving object is in a state of inertia (and the metal slug at point z is in state of inertia in the sense that point Z is not moving closer, or further away, from point X as it orbits. In other words, a CP force keeps an orbiting object moving in an orbit of a "certain fixed" radius, but that CP force must be balanced by a CF force if the orbiting object remains at a "fixed" (constant) distance from the center of the orbit. If one doesn't believe in a CF force, then how do you explain the physics of an orbiting object moving in a circular orbit of fixed radius? Jeff.
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Post by Richie3Jack on Mar 2, 2010 22:12:39 GMT -5
I'm really not sure anymore. Have had some physicists tell me there is no such thing as CF and some scientists say there is and then some just ignore it all together.
Tough to figure what to think.
3JACK
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Post by imperfectgolfer on Mar 3, 2010 0:37:36 GMT -5
I started this thread because I saw a similar thread at BM's forum. www.brianmanzella.com/forum/golfing-discussions/13242-its-real-force-centrifugal-thing-2.htmlOne forum member stated-: "Let's just look at the term "centrifugal force" - the "outward" force - in my example above with the two force vectors. It's the clubhead wanting to move in a straight line - 90 degrees from the string line - at a tangent from the circle. That's the center fleeing force. It certainly wants to move away from the center- but not directly along the shaft or string. So I would call that force vector - centrifugal- center fleeing. And I would call the other force vector- centripetal- whether it moves directly towards the center or not." I believe that his opinions are very wrong. A CF force is only directed opposite in direction to a CP force, which is directed to the center of the circle. In that sense, a CF force is center-fleeing - it moves in a radial direction from the center of the circle to the circumference of the circle (along the shortest path). When a orbiting ball on a string travels constantly along a circular path it also acquires angular momentum as the string is spun at a faster-and-faster speed. That force of acquired momentum will cause the ball to leave at a tangent to the circle if the string is released - if the string is released, then the CP force, and consequently the CF force, immediately disappear and the only force remaining is due the fact that the orbiting ball has already acquired a finite amount of speed, that will cause the ball to move in a linear direction (at a tangent to the circle) when the CP force/CF force disappear. Jeff.
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Post by imperfectgolfer on Mar 3, 2010 0:57:40 GMT -5
Another BM forum member expressed the following opinion - which I think is wrong.
"Yes, friction is what keeps a car from swinging off the road. Friction is a force. Lets take the example of a car driving around a turn. Centrifugal force exist because objects that are in motion want to remain in that motion unless an equal or opposite force acts upon it. In a perfect world, if I am driving a car in a straight line and take my foot off the accelerator and coast. The car will remain at that speed forever. (unless another force acts upon it) It wants to remain at that speed. If I turn the wheel, the friction of the tires has acted upon the momentum of the car and created both centripetal and centrifugal force. The constant "need" for the car to want to stay in a straight line (the mometum) is considered centrifigal force. The force that is preventing the car from going in the straight line is centripital force. If the car's tires (centripital force) ever offer less force then the amount of centrifigal force (icy roads) the car will continue straight (bam)."
If a car is traveling in a straight line, then there must be a linear force that moves the car in a straight line. The car will continue to travel at the same speed in a straight line linear direction from a "certain" amount of energy derived from the car's engine needed to overcome friction of the tires against the surface of the road + the factor of air resistance. That linear force moving the car in a straight line direction is not a CF force, which can only exist when a CP force becomes operant.
When the driver turns the wheel, the friction of the tires against the ground doesn't create either a CP or CF force. The energy moving a car comes from the car's engine, and that energy is transferred to the wheels. When the front wheels start to move along a circular path, then the force causing the wheels to move along a constant circular path can be divided into two components - a linear force that is always directed at a tangent to the circular arc and a combined CP/CF force that is always directed towards/away from the center of the circle. If the CP force and CF force were not balanced, then the car's wheels would move in a spiral (towards the center) and not in a circular arc of constant radius.
Jeff.
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Post by jonnygrouville on Mar 3, 2010 5:21:22 GMT -5
Fact or fiction? Both! We experience it swinging the golf club, so it is real, so fact. As Jeff has asked before, how can we use any of this information to change what we do with the golf club? We need real things. Golf swings work with real things, so fact. It might not strictly be true if you are working in a theoretical frictionless vacuum where you need to understand forces at work in complex systems approaching the speed of light. That's not a golf swing, so fact. However, it is an interesting discussion none-the-less. I had it explained to me using a car example as well, but my theoretical protagonist was sitting in the back seat. Car going straight, constant speed, equilibrium, no problem. Car turns left, man slides right (assuming everything is going quick enough and turning sharply enough to overcome friction, but not so sharp they fly out of their seat). His mass would rather keep going straight on, so he slides down the seat as the car moves left- a feeling of sliding right for him. From a static bird's eye view position directly above the line of initial travel, during the slide, he is still moving in the direction of the initial straight line. The inside of the door then forces him to follow the arc of the turn of the car. The equilibrium of the system is disturbed by the turning of the car, creating an addition vector, an acceleration to a mass resulting in a force. This is not forcing him away from the centre of the arc of the turn of the car. If the car somehow turned left at right angles, he would also be flung against the door. He would experience this force if the car drove around a square. He would experienced force if it drove around in a pentagon, hexagon, etc., but you would never call this centrifugal force. This is experienced as lots of small turns making up an arc as the car is constantly turning resulting in a feeling of constantly being under the influence of a force.
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Post by TeddyIrons on Mar 3, 2010 9:59:40 GMT -5
I view it this way. A force will act in one direction until acted upon by another force. If a stone is being swung on a string, without CP force (the string) the stone will fly off in one direction. The force to change direction is not CF force, as there is no force being applied in the opposite direction of CP force. Instead there is torque, which is force that is continuosly changing direction. So where is the CF force? From this point of view, I can see why CF force is considered fictitious.
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Post by imperfectgolfer on Mar 3, 2010 10:40:48 GMT -5
Teddy
You have presumably not understood my argument.
You state-: "A force will act in one direction until acted upon by another force."
I believe that your statement is logically incoherent. Forces do not act on each other - forces act on an object eg. orbiting ball on a string. An orbiting object can be influenced by mutiple vectoral forces that can affect its direction of travel. When you state that an orbiting ball is subjected to a torque force you are correct. That torque force comes from the string pulling the orbiting ball, and that torque force can be divided into two vectoral force components - a linear force that moves the orbiting ball in a straight line direction (that is at a tangent to the circle) and a CP force that is directed towards the center of the circle. It is the CP force that bends the direction of travel from being straight to being circular. As long as the CP force is present, the orbiting ball will constantly change direction - which is what is responsible for the fact that the ball's path is circular (a circular path is nothing more than a straight line path being constantly bent towards the center of an imaginary circle due to the presence of a CP force).
If the CP force is suddenly increased, then the radius of the imaginary circle is being decreased and the orbiting ball's path will spiral closer to the center (like a moth circling a candle flame). One can mimic that action by pulling on the string (at its location between the thumb and index finger) so that the length of the string becomes slowly shorter and shorter. That pulling force on the string is equivalent to a pure CP force because it is pulling the orbiting ball closer to the center of the circle. If the orbiting ball stops moving towards the thumb-index finger (center of the circle), and maintains an orbit of constant radius, then it means that another force has balanced the CP force, and that force is the CF force. According to Newton's third law, a force must be balanced by an equal and opposite force if a moving object is in a state of motional inertia - and an orbiting ball is in a state of circular inertia if the radius of the circular orbit doesn't change.
Jeff.
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Post by imperfectgolfer on Mar 3, 2010 11:08:28 GMT -5
Jonny,
I suspect that you are correctly understanding the situation of man sitting in the back seat of car.
When the car is traveling in a straight line direction at a constant linear speed, the man in the back seat is traveling at the same speed in a straight line direction. When a driver turns the steering wheel counterclockwise to direct the car to turn leftwards, then the car is being subjected to a new vectoral force. However, the man in the backseat is not being subjected to that same new vectoral force. In that sense he is still in his state of motional inertia - only being subjected to the same linear force that was present when the car was traveling in a straight line at a constant speed. The man in the backseat only gets subjected to a new vectoral force when he bangs against the inside of the right back-door that deflects him in the same new leftwards direction that the car is now traveling.
Jeff.
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Post by TeddyIrons on Mar 3, 2010 15:49:45 GMT -5
Teddy If the CP force is suddenly increased, then the radius of the imaginary circle is being decreased and the orbiting ball's path will spiral closer to the center (like a moth circling a candle flame). One can mimic that action by pulling on the string (at its location between the thumb and index finger) so that the length of the string becomes slowly shorter and shorter. That pulling force on the string is equivalent to a pure CP force because it is pulling the orbiting ball closer to the center of the circle. If the orbiting ball stops moving towards the thumb-index finger (center of the circle), and maintains an orbit of constant radius, then it means that another force has balanced the CP force, and that force is the CF force. According to Newton's third law, a force must be balanced by an equal and opposite force if a moving object is in a state of motional inertia - and an orbiting ball is in a state of circular inertia if the radius of the circular orbit doesn't change. Jeff. I disagree. It is still torque that is fighting the CP force, not CF force. There is a continuous change of direction in a stone swinging on a piece of string. That is what is fighting the CP force, whether it be a spring or a slack piece of string.
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Post by imperfectgolfer on Mar 3, 2010 19:20:26 GMT -5
Teddy,
You wrote-: "There is a continuous change of direction in a stone swinging on a piece of string. That is what is fighting the CP force."
We definitely think of this particular issue in a different way, because I believe that a CP force causes the continuous change in direction of the orbiting ball's (stone) movement in space from being straight to being continuously circular.
Jeff.
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Post by jonnygrouville on Mar 3, 2010 20:21:51 GMT -5
Exactly Jeff!
This is the argument used against centrifugal force, that you can break the car driving in a circle down to lots and lots and lots of small individual turns that make up the circular motion so there is no 'new' force with a different name.
Theoretically interesting, yes. Practically useful, no. It is still not going to help me stop hooking my three wood.
Good discussion though. Enjoyed that.
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Post by imperfectgolfer on Mar 3, 2010 21:07:09 GMT -5
Jonny,
I realize that this discussion will not help you stop hooking the ball, but it is nevertheless useful for a golfer to understand general concepts of Newtonian physics.
Let's take that back seat passenger again. I presume that you are saying that a circular path (as experienced by the car) is merely an endless series of small changes in conversion of a straight line path to a circular path by a continuous left-turn action. In that model, there are presumably two vectoral forces at play - a straight line vectoral force and a CP force that continuously bends the car's path to the left and creates a continuous circular motion - and that there is no need to think of a CF force. If correct - I can understand that line of thinking.
However, what about the back seat passenger who is a free-floating body within the car compartment. If he is not restrained by a seat belt (which forces him to turn with the car) is he is not always in a state of continuous outward motion relative to the car's circular path and that continuous motion jams him continuously against the inside of the right-side back door. In other words, he can be thought of as experiencing a CF force and the pressure of the right-side car door against his body represents a restraining force (equivalent to a CP force) that keeps his free-floating body moving along a circular path (in concert with the car's circular direction of travel).
Jeff.
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Post by jonnygrouville on Mar 4, 2010 1:27:46 GMT -5
Again, exactly. Theory and practical application. Centrifugal force remains relevant from a practical application perspective.
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Post by TeddyIrons on Mar 4, 2010 2:29:51 GMT -5
Teddy, You wrote-: "There is a continuous change of direction in a stone swinging on a piece of string. That is what is fighting the CP force." We definitely think of this particular issue in a different way, because I believe that a CP force causes the continuous change in direction of the orbiting ball's (stone) movement in space from being straight to being continuously circular. Jeff. Well Jeff I also agree with the statement that the CP force causes the continuous change in direction, hence the orbiting ball. That does not mean there is a CF force, however.
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foo
Beat up Radials
Posts: 4
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Post by foo on Mar 4, 2010 3:28:13 GMT -5
I've never understood why this causes such confusion. Did no one watch Mr. Wizzard when they where growing up? Maybe this quote will help clear things up. "The confusion is one of nomenclature as well as physics. The usual meaning of "centrifugal" force, when correctly used, is not the same as the Newton 3 reaction to centripetal force. The commonly misconceived term, centrifugal force, refers to a non-existent force on the object moving in a circle, tending to make it want to move in a straight line. The Newton 3 reaction to centripetal force is perfectly legitimate, and you can call it what you want, but it is not a force on the object under consideration, it is a force on something else. The myth that needs to be eliminated regarding this "force", is the one that says that when you are in a car that is going round a corner, there is a force on you tending to move you in a straight line. You can even feel it! This is false. This is the mythical centrifugal force." If the term fictitious or pseudo force is too loaded then use the term inertia force. It is an effect that an object experiences in an accelerating frame of referince because of its inertia. A physicists would call it fictitious not because it doesn't have an effect but because they can transform the situation into a non-acceleration frame and describe it with less forces or with forces that won't break Newtow's third law. What if you took the passenger in the car example but instead of turning the wheel the driver stepped on the gas. The passenger might say "Do you feel that? That is a backward seeking force." If the driver was a physicist he would say that it was just a pseudo force, it was just the passagner resiting the car's acceleration. Of course nobody really understands what or how inertia is (though Mach gave it a try en.wikipedia.org/wiki/Mach%27s_principle) so maybe you're better of with the pseudo forces. There is a good wikipedia page on this. en.wikipedia.org/wiki/Fictitious_forces
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