Question for mandrin
- Thread starter Ringer
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So what you're saying is that you guys agree?
Yup, on how limited Newtonian physics is.. yup.
mandrin
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Ringer,
Logic is not quite your strongest asset. Let me show you why.
- The centripetal force is the only force acting on the rotating object.
- Letting go simply eliminates this force and the object continues tangentially.
- Conclusion: The experiment reveals absolutely nothing about centrifugal force.
Keep trucking
Steve - you state that an object must move in a radial direction away from the centre in order for a centrifugal force to be proven to be present.
If I understand the situation of the ball-on-a-string correctly, a centripetal force keeps the object moving along a circular path (rather than a straight line path) because that centripetal force is centrally-directed. Therefore, the absence of that centripetal force will cause the moving object to no longer move along a centripetally-induced circular path - and it is now moving in response to other forces AWAY from the circular path, and therefore AWAY from the centre. Those OTHER forces can be perceived to be centrifugal force influences, which are manifested by the change in direction - from a circular path (towards the center) to a tangential straight line path (away from the center).
Conceptually, it may be reasonable to conclude that an object moving CONTINUOUSLY along a circular path (rather than a spiralling path towards the center - like a moth drawn to a candle flame) must have any centripetal force balanced by a centrifugal force of equal magnitude, and that the centrifugal force only becomes manifest when the centripetal force lessens or disappears. When the centripetal force lessens, the moving object can no longer be kept on a circular path and it will move further AWAY from the center. It will not move in a radial direction because the moving object has also gained momentum during its circular path passage and that momentum carries it in a straight line direction.
Jeff.
If I understand the situation of the ball-on-a-string correctly, a centripetal force keeps the object moving along a circular path (rather than a straight line path) because that centripetal force is centrally-directed. Therefore, the absence of that centripetal force will cause the moving object to no longer move along a centripetally-induced circular path - and it is now moving in response to other forces AWAY from the circular path, and therefore AWAY from the centre. Those OTHER forces can be perceived to be centrifugal force influences, which are manifested by the change in direction - from a circular path (towards the center) to a tangential straight line path (away from the center).
Conceptually, it may be reasonable to conclude that an object moving CONTINUOUSLY along a circular path (rather than a spiralling path towards the center - like a moth drawn to a candle flame) must have any centripetal force balanced by a centrifugal force of equal magnitude, and that the centrifugal force only becomes manifest when the centripetal force lessens or disappears. When the centripetal force lessens, the moving object can no longer be kept on a circular path and it will move further AWAY from the center. It will not move in a radial direction because the moving object has also gained momentum during its circular path passage and that momentum carries it in a straight line direction.
Jeff.
mandrin
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JeffMann,
Don’t think of the mass circulating with constant angular speed around a center as indicating there being a state of force balance.
Centrifugal and centripetal force don’t have the same point of application and hence can’t balance notwithstanding having equal and opposing magnitudes.
For a mass to circle around a center there has to be a net force, hence force unbalance, to continuously accelerate the mass towards the center.
Mandrin - you state "For a mass to circle around a center there has to be a net force, hence force unbalance, to continuously accelerate the mass towards the center."
I cannot understand this statement. Surely, the mass is NOT continuously accelerating towards the center if it is travelling CONTINUOUSLY in a circle. It is no closer to the center at any single point in time if the radius of its circular path remains constant. If there is a centripetal force constantly pulling the mass to the center, but the mass is not getting any closer to the center (because the radius of the circle remains unchanged), then is it not reasonable to postulate the presence of another force opposing the centripetal force?
Jeff.
I cannot understand this statement. Surely, the mass is NOT continuously accelerating towards the center if it is travelling CONTINUOUSLY in a circle. It is no closer to the center at any single point in time if the radius of its circular path remains constant. If there is a centripetal force constantly pulling the mass to the center, but the mass is not getting any closer to the center (because the radius of the circle remains unchanged), then is it not reasonable to postulate the presence of another force opposing the centripetal force?
Jeff.
Then you folks will forever remain ignorant.
http://math.ucr.edu/home/baez/physics/General/Centrifugal/centri.html
I doubt University of Cal is poor source.
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Bronco Billy
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Hi There
Very Powerful and Informative Article...... My Opinion is that That Ringer and Mandrin are Both Right depending on How One wants to Solve a Particular Problem..... The solutions to a Particular Problem would essentially be the Same whether one uses Newtonian or Einstonian Physics.........
Cheers
mandrin
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Jeff,
It suffices to do a quick search on centripetal force to find many excellent explanations.
The circling object is constantly accelerating towards the center. However it is not getting any closer since it is also tangentially moving away from it.
Wikipedia:
The velocity vector is defined by the speed and also by the direction of motion.
Objects experiencing no net force do not accelerate and, hence, move in a straight line with constant speed: they have a constant velocity.
However, an object moving in a circle at constant speed has a changing direction of motion. The rate of change of the object's velocity vector is the centripetal acceleration.
Which is why it's problematic. Physics is supposed to be all-encompasing. It shouldn't matter what frame of reference you have. And that's what Einstein had trouble with... which is what lead to General Relativity.
Mandrin - I can accept the idea that the object remains on a CONSTANT circular path because its centripetal acceleration is balanced by another force - that other force being its tangential acceleration, which I like to think of as being a "centrigugal force" even if it is not scientifically exact/true. See - http://www.glenbrook.k12.il.us/gbssci/phys/Class/circles/u6l1d.html
Jeff.
Jeff.
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Vicious Circle
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I can't get used to the term "acceleration" used instead of "change in direction" I've substituted these in the above quote.
Would it be incorrect to say "circular direction"? (I'm guessing it would)
mandrin
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rotating frames & black holes
Simple question – how many of you have played golf inside a rotating reference frame re to earth? Should be really fun, any problem getting the ball into the hole?
Ringer before you take everyone up into some big black hole, can you still address a simple earthy mundane logic problem as posed by post #124.
Simple question – how many of you have played golf inside a rotating reference frame re to earth? Should be really fun, any problem getting the ball into the hole?
Ringer before you take everyone up into some big black hole, can you still address a simple earthy mundane logic problem as posed by post #124.
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