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#71
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Can I set my own bindings?
"Walt" wrote in message ... VtSkier wrote: Walt wrote: VtSkier wrote: From wiki http://en.wikipedia.org/wiki/Vector_(spatial) "In physics and in vector calculus, a spatial vector, or simply vector, is a concept characterized by a magnitude and a direction." Yeah. Ok. Further down the page, magnitude is intentionally used interchangeably with "length" in effect saying it's the same thing. Yes, the magnitude of a position vector is the same thing it's length. Then "magnitude" = "distance", to which you add "direction" to define "torque" as opposed to "work". The only difference. Um, you lost me around that last curve. WTF? Think of it this way: I'm testing a binding. I place a boot in the binding and apply a torque of, say, 50 Newton Meters. The binding doesn't release. I've just described a situation where there is torque but no motion. Do you say there is no torque here? If so, how does one ever test a binding? You are NOT applying TORQUE to the torque wrench, you are only applying FORCE of 50 Newtons. There is no TORQUE until there is movement (of the binding releasing). As soon as you apply force you are applying torque. The two go hand in hand, you can't have one without the other. See the definition of torque: T = F X r . All you need is force and a moment arm, you do not need motion. I can't make it any clearer. I don't know where you got the erroneous idea that torque requires motion, but it's wrong. Trust me. It's wrong. It's not in the definition of torque. You are measuring POTENTIAL TORQUE, which the wrench reads in Newton-Meters because when the TORQUE happens (by movement) that's what it will be. There is no such thing as POTENTIAL TORQUE, at least not in physics. You are insistent that the torque doesn't exist until something moves, so you've invented a red herring concept to explain the existence of something that's obviously there but theoretically impossible in your belief system. Get out Dr Occam's razor and excise this unnecessary complication. When you apply the force, there is also an applied torque. Regardless of whether anything moves. Get it? Force implies torque, torque implies force. Where there is one there is the other *by definition*. And since we agree that it's possible to have force without motion it is also possible to have torque without motion. I've been saying this all along except that TORQUE cannot exist without motion. Yes, I know that that's what you've been saying. And I've been saying that every physics text written in the last 300 years disagrees with you. //Walt // //this is why I usually don't argue physics on usenet Are you two not saying the same thing? Both of you mentioned that to have torque something must move am I correct? I guess the difference in your argument is what must move. The item that is being torqued or the item doing the torqueing. As I understand your arguments as long as there is movement in an arc or rotational direction from an applied force there is torque, correct? If this is correct then once a force is applied there is movement no matter how small, no movement no force. Did I understand everything? JQ Dancing on the edge |
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#72
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Can I set my own bindings?
VtSkier wrote:
Here's a more visceral example: pick up a brick and hold it straight out in front of you with your arm horizontal. Hold it still. Then please try to explain, without allowing the brick to move, how there is no torque since there is no motion. There is FORCE but no TORQUE Ok. Change the brick out for a ski. Grasp it by the binding and hold it vertically. Not that hard, is it? Now grasp it by the tail and (try to) hold it horizontally. Much harder, right? Why? What makes one so much harder than the other? The force hasn't increased, since the ski weighs the same as it did before. So what makes it so much harder? HINT: torque. I double dog dare you to hold a ski like that and tell me that you don't feel the difference. //Walt |
#73
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Can I set my own bindings?
Walt wrote:
(snip) When you apply the force, there is also an applied torque. Regardless of whether anything moves. Get it? No Force implies torque, torque implies force. Force can PRODUCE torque, torque CONTAINS a force component. Where there is one there is the other *by definition*. And since we agree that it's possible to have force without motion it is also possible to have torque without motion. I cannot find a single definition of torque that doesn't require motion that is either happening or is about to happen. Including a text book definition with begins with a discussion of angular momentum and its relationship to torque. http://www.lightandmatter.com/html_b...ch05/ch05.html One of the problems here seems like an unconventional use of a common tool, the torque wrench. The way this tool is commonly used it to determine that a nut is tight enough to not back itself off but not so tight as there is the danger of stripping the threads. This is really the intended use of a torque wrench. The way it's used is that you turn the nut with the wrench until the indicator says that you have reached the correct value. When that happens, you stop turning. While you are turning (moving, angular momentum) you are applying torque. When you stop, you no longer are. (snip) |
#74
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Can I set my own bindings?
JQ wrote:
Are you two not saying the same thing? Both of you mentioned that to have torque something must move am I correct? No. VtSkier is saying that in order to have torque something must move. I am saying it is incorrect. Please, let's not get into an argument over whether we're having an argument. We are, the point of contention is clear. I guess the difference in your argument is what must move. NOTHING has to move for there to be torque. //Walt |
#75
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Can I set my own bindings?
Walt wrote:
(snip) Force implies torque, torque implies force. Where there is one there is the other *by definition*. And since we agree that it's possible to have force without motion it is also possible to have torque without motion. No I don't. http://www.lightandmatter.com/html_b...ch05/ch05.html Torque distinguished from force Of course a force is necessary in order to create a torque --- you can't twist a screw without pushing on the wrench --- but force and torque are two different things. One distinction between them is direction. We use positive and negative signs to represent forces in the two possible directions along a line. The direction of a torque, however, is clockwise or counterclockwise, not a linear direction. And then it goes on to add the leverage component of torque. And I'm not real happy with this guy's definitions either. It feels like he is confusing force and work/energy by saying, "We use positive and negative signs to represent forces in the two possible directions along a line." Which says to me that "force" as he is using it, has motion/distance associated with it. |
#76
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Can I set my own bindings?
Walt wrote:
Richard Henry wrote: Is this replacing the annual percent-slope-versus-angle thread? Ya know, I don't recall having this particular argument on RSA before. And it's been years since we've had a good percent-slope-versus-angle dust up. Anyway, if you want to have an argument with me you'll have to pay up like the other Richard. Would you like the 5 minute version, or do you want to go for the full hour? //Walt ****, if you are as bored as I am, go for the full hour. Or go skiing. |
#77
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Can I set my own bindings?
VtSkier wrote:
Walt wrote: I cannot find a single definition of torque that doesn't require motion that is either happening or is about to happen. That's odd, since I've only posted it about 5 times. Here it is again: T = r x F where F is the force and r is the moment arm vector. Now, what, exactly, is in motion here? A force, acting on a moment arm produces torque. We agree that it's possible for a force to exist without motion. The above definition shows that a stationary force will produce torque. I really can't make this any clearer. If I didn't know you better I'd say that you were just trolling. //Walt |
#78
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Can I set my own bindings?
VtSkier wrote:
Walt wrote: Force implies torque, torque implies force. Where there is one there is the other *by definition*. And since we agree that it's possible to have force without motion it is also possible to have torque without motion. No I don't. You don't what? You don't agree that it's possible to have force without motion? Or what? http://www.lightandmatter.com/html_b...ch05/ch05.html Torque distinguished from force Of course a force is necessary in order to create a torque --- you can't twist a screw without pushing on the wrench --- but force and torque are two different things. One distinction between them is direction. We use positive and negative signs to represent forces in the two possible directions along a line. The direction of a torque, however, is clockwise or counterclockwise, not a linear direction. And then it goes on to add the leverage component of torque. And I'm not real happy with this guy's definitions either. It feels like he is confusing force and work/energy by saying, "We use positive and negative signs to represent forces in the two possible directions along a line." Which says to me that "force" as he is using it, has motion/distance associated with it. I can't say I care much for his presentation either. It suffers from a common problem: trying to explain physics without vector calculus. When you try this you wind up dancing around things with vague statements about directions and magnitudes, everything is done with scalars and with some hand waving argument about what direction grafted on at the end. Things get muddy. High school physics, which is usually taught without calculus, is particularly suceptible to this phenomenon. //Walt |
#79
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Can I set my own bindings?
On Feb 19, 1:05 pm, VtSkier wrote:
Richard Henry wrote: Is this replacing the annual percent-slope-versus-angle thread? Do you want to start that one? Well, there hasn't been enough snow this year to get the avalanche threads burning. |
#80
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Can I set my own bindings?
Richard Henry wrote:
On Feb 19, 1:05 pm, VtSkier wrote: Richard Henry wrote: Is this replacing the annual percent-slope-versus-angle thread? Do you want to start that one? Well, there hasn't been enough snow this year to get the avalanche threads burning. Yeah. Only six avalanche fatalities last weekend. Hardly even worth mentioning. http://www.greatfallstribune.com/apps/pbcs.dll/article?AID=/20070219/NEWS03/70219007 //Walt |
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