Motion
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From: Randy Poe on 3 Oct 2005 11:02 TomGee wrote: > Randy Poe wrote: > > In my universe, if two things are the same by definition, > > they're equal. > > > > > Yes, but in the real universe, they're not always equal. In the real universe, things that are the same are always equal. > What objects > or quantities or properties are equal to depends on more than just an > equal sign. If you say, "These two mountains are equal", the statement > is nonsense. But so is the sentence "those two mountains are the same." > For it to make sense, you must qualify it something to > compare the two, height, area, mineral amounts, difficulty in climbing, > etc. If I were to say "the heights of those two mountains are them same" I would also mean "the heights of those two mountains are equal". Ditto for difficulty, mineral content, or surface area. I can't imagine a situation where I would use "same" but also mean "not equal". > > That makes no sense. Again, if two things are the same thing, > > they're equal. > > > Yes, in your universe. OK, having rejected logic, you now reject A = A. > > > > By the Tipler quote that says force is the time rate of change > > > > of momentum? > > > > > > > > Again, how does that prove that F = dp/dt is wrong? > > > > > > > > > > > Another one of your bad inferences. > > > > Tipler said that force is the time rate of change of momentum. > > That's not an "inference", it's in the quote you provided. > > > > Above, you claim the Tipler quote proves me wrong. > > > In your universe, proving you wrong equals proving F=dp/dt wrong, so > that's why you inferred I said that. What else are we arguing about? What do you think the Tipler quote proves me wrong ABOUT? I see nothing in the Tipler quote to disagree with. > > Well, I did, actually. It's true in non-relativistic situations, > > but not in general. > > > But in your universe relativistic situations are reality while in our > real universe, relativistic situations are imaginary. Not only are > your eyes crossed, but your brain is upside down. No comment. Every one of your pronouncements is a gem. > > > > Nor can I see how "work done on an object equals change in > > > > KE of the object" contradicts "force and momentum are not > > > > interchangeable". > > > > > > > Aren't you the one who said KE is not changed by an external force? > > > > No, I never said such a thing. Can you provide the quote where > > you garbled that inference from? Can you? - Randy
From: Randy Poe on 3 Oct 2005 11:02 Randy Poe wrote: > TomGee wrote: > > Aren't you the one who said KE is not changed by an external force? > > No, I never said such a thing. Can you provide the quote where > you garbled that inference from? > I think I can save you some work. I said that in the case of circular motion, the force does not do any work on the object, and it also does not change the KE. The reason the force does not do any work in that situation is that the motion and the force are at right angles. When a force does work, it changes the KE. As Tipler says, the amount of work done is equal to the change in KE. In the case of circular motion, even though there is an external force, the amount of work done = 0, and the change in KE = 0. As I recall, I brought up this example because you were accusing somebody else of saying that force never changes KE, and I was guessing that that person meant circular motion, since you didn't provide an actual quote to support your accusation. - Randy
From: Don1 on 3 Oct 2005 20:52 Randy Poe wrote: > Randy Poe wrote: > > TomGee wrote: > > > Aren't you the one who said KE is not changed by an external force? > > > > No, I never said such a thing. Can you provide the quote where > > you garbled that inference from? > > > > I think I can save you some work. I said that in the case of > circular motion, the force does not do any work on the object, > and it also does not change the KE. > Are you saying that a force acting at right angles to a moving body is not doing any work. or changing the Kinetic energy as it changes the directin? I find this hard to believe. I think we need to study this situation with a fine tooth comb. > The reason the force does not do any work in that situation > is that the motion and the force are at right angles. > > When a force does work, it changes the KE. As Tipler says, the > amount of work done is equal to the change in KE. In the case > of circular motion, even though there is an external force, > the amount of work done = 0, and the change in KE = 0. > > As I recall, I brought up this example because you were accusing > somebody else of saying that force never changes KE, and I > was guessing that that person meant circular motion, since > you didn't provide an actual quote to support your accusation. > > - Randy
From: PD on 3 Oct 2005 21:34 Don1 wrote: > Randy Poe wrote: > > Randy Poe wrote: > > > TomGee wrote: > > > > Aren't you the one who said KE is not changed by an external force? > > > > > > No, I never said such a thing. Can you provide the quote where > > > you garbled that inference from? > > > > > > > I think I can save you some work. I said that in the case of > > circular motion, the force does not do any work on the object, > > and it also does not change the KE. > > > Are you saying that a force acting at right angles to a moving body is > not doing any work. or changing the Kinetic energy as it changes the > directin? I find this hard to believe. I think we need to study this > situation with a fine tooth comb. It's indeed true, Don. That's in an early chapter in most middle-school physical science books. PD > > > The reason the force does not do any work in that situation > > is that the motion and the force are at right angles. > > > > When a force does work, it changes the KE. As Tipler says, the > > amount of work done is equal to the change in KE. In the case > > of circular motion, even though there is an external force, > > the amount of work done = 0, and the change in KE = 0. > > > > As I recall, I brought up this example because you were accusing > > somebody else of saying that force never changes KE, and I > > was guessing that that person meant circular motion, since > > you didn't provide an actual quote to support your accusation. > > > > - Randy
From: Don1 on 4 Oct 2005 09:24
PD wrote: > Don1 wrote: > > Randy Poe wrote: > > > Randy Poe wrote: > > > > TomGee wrote: > > > > > Aren't you the one who said KE is not changed by an external force? > > > > > > > > No, I never said such a thing. Can you provide the quote where > > > > you garbled that inference from? > > > > > > > > > > I think I can save you some work. I said that in the case of > > > circular motion, the force does not do any work on the object, > > > and it also does not change the KE. > > > > > Are you saying that a force acting at right angles to a moving body is > > not doing any work. or changing the Kinetic energy as it changes the > > directin? I find this hard to believe. I think we need to study this > > situation with a fine tooth comb. > > It's indeed true, Don. That's in an early chapter in most middle-school > physical science books. > > PD Your quote of middle school science books constitutes positive proof in your mind, and might even stand up in a court of law, but it's a crock. > > > > > > The reason the force does not do any work in that situation > > > is that the motion and the force are at right angles. > > > > > > When a force does work, it changes the KE. As Tipler says, the > > > amount of work done is equal to the change in KE. In the case > > > of circular motion, even though there is an external force, > > > the amount of work done = 0, and the change in KE = 0. > > > > > > As I recall, I brought up this example because you were accusing > > > somebody else of saying that force never changes KE, and I > > > was guessing that that person meant circular motion, since > > > you didn't provide an actual quote to support your accusation. > > > > > > - Randy When a force acts at right angles to a moving body, the body is turned, and curves away from the force; not instantaneously but proportional to the magnitude of the force and it's duration. If the body responded instantaneously there would be an inward jump instead of a curve, and a ratchet effect would result. Instead, the force displaces the moving body, resulting in elliptical curvature. |