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#51
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Can I set my own bindings?
Walt wrote:
VtSkier wrote: Walt wrote: ... torque is force applied at some distance, Yes, but isn't that what WORK/ENERGY is? Work is force acting though a distance: W = F(dot)d. With torque, the force is perpendicular to the distance vector , so when you compute the dot product you get zero. Torque, like distance and force, is a vector quantity while energy (work) is a scalar. To compute torque, you take the vector cross product of force and position vector: T = F x d. This gives a vector, unlike the dot product above which gives a scalar. To say a vector (torque) is equal to a scalar (energy) is like saying Wednesday is equal to cheese. It makes no sense. //Walt Whether or not torque and work are directly equivalent, they are use interchangeably in many ways. By adding the element of time to work we get the concept of "horsepower". When James Watt observed that a horse, on average, could lift (I'm sure he used "lift" in some way so that he didn't have (much) friction to deal with) 550 pounds one foot in one second, he decided that moving 550 pound, one foot in one second would be a measure of power called "One Horsepower". This is all well and good. The "work" is linear and the time it takes to do the work is one second. When talking about engines which produce useful work in a rotational way, we speak of torque and horsepower. Horsepower being basically the speed at which the torque is produced. We don't need to get into the various uses of that power which requires maximum horsepower to be produced at low speed or high speed, that's the subject of another discussion and is not germain to this one. The "horsepower" unit was devised for the speed of linear work. It is very useful in describing the speed of rotational work. Torque is not a vector, it is work applied in a vector (rotational) direction. Some of your earlier argument suggested that torque can be measured if the the object that the torque is being applied to does not move. I suggested that while the *potential* torque can be measured there is no work/torque performed until the object moves. Yes, you can apply a lot of force and still not have the nut move. You can also apply a lot of force trying to move a rock and no work is accomplished until the rock does move, in a linear way. This is directly analogous to to the nut not moving in your example. The reason that torque and work/energy use the same units is that they really are the same thing. If the thing doesn't move, there is only force, no work or torque. If the thing moves over a distance, linear or rotational, there is work/ torque. If you measure the rate at which this work or torque is taking place, the unit you use to describe either linear or rotational power is *horsepower*. The argument I'm making here is that the only difference between force/work and torque is the direction the force is applied. Linear for force/work, rotational/vector for torque. |
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#52
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Can I set my own bindings?
VtSkier wrote:
Torque is not a vector, Um....no. It is most certainly a vector quantity. Please see http://en.wikipedia.org/wiki/Torque , or if you're a stickler for reliable sources, any elementary physics text like Hailliday and Resnick, or Sears and Zemansky. You're mixing concepts. Yes, torque is *related* to power, which is *related* to energy, which is *related* to momentum (both linear and angular) but these are all distinct concepts. Once you've sorted it out we can talk. //Walt |
#53
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Can I set my own bindings?
Walt wrote:
VtSkier wrote: Torque is not a vector, Um....no. It is most certainly a vector quantity. not to be too much of a stickler here, Torque is not a vector quantity, it HAS a vector quantity. As opposed to a straight line quantity as in work/power which is what I've been saying. Please see http://en.wikipedia.org/wiki/Torque , or if you're a stickler for reliable sources, any elementary physics text like Hailliday and Resnick, or Sears and Zemansky. You're mixing concepts. Yes, torque is *related* to power, which is *related* to energy, which is *related* to momentum (both linear and angular) but these are all distinct concepts. Once you've sorted it out we can talk. //Walt |
#54
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Can I set my own bindings?
Walt wrote:
VtSkier wrote: Torque is not a vector, Um....no. It is most certainly a vector quantity. Please see http://en.wikipedia.org/wiki/Torque , or if you're a stickler for reliable sources, any elementary physics text like Hailliday and Resnick, or Sears and Zemansky. You're mixing concepts. Yes, torque is *related* to power, which is *related* to energy, which is *related* to momentum (both linear and angular) but these are all distinct concepts. Once you've sorted it out we can talk. //Walt Having read the wiki, I don't see much difference in what I've been saying. At one point you claimed that you were exerting torque on a nut if you were *trying* to turn it. In "common usage", you are correct, but not according to the definitions in the wiki, which do agree with my sophomore in high school text books. Also, if there are definitions which pertain to particle or nuclear physics, I'm not aware of them and don't pretend to be applying them. Where is Physics Man when you need him? In all of the wiki, I can find no instance where if there is no motion there is torque. Stated the other way, if there is no motion, there is no torque. Yes, there are special cases and special definitions to suit one's specialty be it lever design or auto mechanics. But from what I've seen, torque is work in a rotational or angular mode. Certainly this is what torque is when applied to the rating of an automobile engine. |
#55
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Can I set my own bindings?
VtSkier wrote:
Having read the wiki, I don't see much difference in what I've been saying. Here are the differences: You are confusing two distinct concepts, torque and work. They are different but related ideas. They are *not* the same. You are saying that torque is not a vector. It is. You are saying that there must be motion to have torque. Not true. See below. In all of the wiki, I can find no instance where if there is no motion there is torque. Look again. Here's the definition of torque: Mathematically, the torque on a particle (which has the position r in some reference frame) can be defined as the cross product: Tau = r X F where r is the particle's position vector F is the force acting on the particle, So, to have torque, all you need is a force. There does not have to be motion. It's the cross product of two vectors, so it is by definition a vector. Stated the other way, if there is no motion, there is no torque. No. 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? torque is work in a rotational or angular mode. Torque produces work when there is motion, according to W = T dot theta (where theta is the angle the torque moves through and dot is the vector dot product). The relationship between torque and work is very simple, but the two are different concepts. Similarly, force produces work when there is motion, according to W = F dot d (where d is the distance the force acts through and again dot is the vector dot product). Here force and work are related in a very simple manner, but that doesn't mean that force *is* work. They are different but related concepts. In particular, force can exist without motion. When that happens, there is no work. Likewise torque can exist without motion. Again there is no work if there is no motion. //Walt |
#56
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Can I set my own bindings?
Walt wrote:
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? What are the springs doing? Are they not being compressed motion? I was trying to think of a torque but no motion example but it seems to depend where you measure something. If you take a dragster with automatic transmissions on the start line, engine loaded brakes locked would be my example. If you look at whole picture it fits statement if you look at componets it fails. |
#57
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Can I set my own bindings?
Walt wrote:
VtSkier wrote: Having read the wiki, I don't see much difference in what I've been saying. Here are the differences: You are confusing two distinct concepts, torque and work. They are different but related ideas. They are *not* the same. You are saying that torque is not a vector. It is. You are saying that there must be motion to have torque. Not true. See below. In all of the wiki, I can find no instance where if there is no motion there is torque. Look again. Here's the definition of torque: Mathematically, the torque on a particle (which has the position r in some reference frame) can be defined as the cross product: Tau = r X F where r is the particle's position vector F is the force acting on the particle, So, to have torque, all you need is a force. There does not have to be motion. It's the cross product of two vectors, so it is by definition a vector. 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." Further down the page, magnitude is intentionally used interchangeably with "length" in effect saying it's the same thing. Then "magnitude" = "distance", to which you add "direction" to define "torque" as opposed to "work". The only difference. Stated the other way, if there is no motion, there is no torque. No. 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). 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. Another example. If I have an object that WEIGHS one pound, I have to apply a FORCE of at least one pound in the direction opposite to the FORCE provided by gravity in order to lift it. There is NO WORK until I have moved the object a distance. There certainly is FORCE being applied, but until the object is moved, there has been only POTENTIAL WORK. By all the definitions you have supplied, both TORQUE and WORK require movement of a force over a distance. torque is work in a rotational or angular mode. Torque produces work when there is motion, according to W = T dot theta (where theta is the angle the torque moves through and dot is the vector dot product). The relationship between torque and work is very simple, but the two are different concepts. Yes, but look at the definition of VECTOR Similarly, force produces work when there is motion, according to W = F dot d (where d is the distance the force acts through and again dot is the vector dot product). Here force and work are related in a very simple manner, but that doesn't mean that force *is* work. They are different but related concepts. That's correct, but force does not have a movement (distance, vector, etc.) component. In particular, force can exist without motion. When that happens, there is no work. Likewise torque can exist without motion. Again there is no work if there is no motion. I've been saying this all along except that TORQUE cannot exist without motion. TORQUE is a measure of WORK in a specified direction. I think the confusion comes in everyday usage as opposed to scientific usage. Our measuring tools do this to us also. A Torque Wrench, as you appropriately point out is notated in measures of torque, newton-meters or pound- feet. Mine is an old one and is in foot-pounds (exactly analogous to pound-feet) and I've used the ski shop wrenches calibrated in newton-meters. Like the lifting an object example, you apply force to the wrench and no torque exists until the binding releases. The potential torque is what you are measuring, which IS Force, but once again, no torque until the thing moves (in a rotational way, a vector). |
#58
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Can I set my own bindings?
down_hill wrote:
Walt wrote: 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? What are the springs doing? Are they not being compressed motion? I was trying to think of a torque but no motion example but it seems to depend where you measure something. If you take a dragster with automatic transmissions on the start line, engine loaded brakes locked would be my example. If you look at whole picture it fits statement if you look at componets it fails. In the binding: The springs are providing a force to oppose the preset release setting until the force needed to release the binding has been reached. At which point there will be torque because motion has been added to the force. In some (most, I hope) bindings, the springs will compress to provide "flexibility" and a return to center when release potential is reached but only momentarily and I guess that torque is produced in this scenario because there certainly is motion, but to that point at which the motion begins, you have only applied force or potential torque to the binding, and the torque wrench will measure the point at which that motion begins. In the dragster: Because the parts in the engine are moving, there is torque. This is a measure of work. Because you are not allowing the dragster to move, this torque is being dissipated as heat in the transmission until you dump the brakes when it will be sent immediately to the drive wheels. In the dragster as whole, the engine is producing torque because the engine parts are moving. This torque is sent as force to the transmission and drive wheels which converts this force to work (moving down the drag strip). In terms of the dragster, the work is "potential" until you dump the brakes. Potential work is only force. The brakes are not loaded, the transmission is. The brakes are simply allowing the transmission to be loaded. An automatic transmission can be visualized as two fans, one driven by an engine and one to drive a set of rear wheels, opposing each other in a fluid (transmission fluid). Now simplify this. Take a motorized fan and opposite to this place a pinwheel. If you start up the fan, the pinwheel will accelerate to the speed of the fan just very slightly slower than the driven fan. Now hold the pinwheel in place with you hand (brake) until the driven fan is up to speed. The pinwheel will accelerate to the speed of the driven fan in the blink of an eye. This is what the dragster is doing for maximum acceleration, the skill comes from the driver knowing when the drive wheels will break loose and acceleration will be compromised. A car is too complex a machine to use as an example of just one thing or concept because a whole lot of things are happening at the same time. |
#59
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Can I set my own bindings?
down_hill wrote:
Walt wrote: 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? What are the springs doing? Are they not being compressed motion? As you increase the torque from zero to 50 the springs compress, and there is a small amount of motion. Once you reach 50 and stop increasing the torque the system reaches a steady state where there is no motion. At that point there is torque but no motion. I was trying to think of a torque but no motion example... 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. //Walt |
#60
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Can I set my own bindings?
Is this replacing the annual percent-slope-versus-angle thread?
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