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#101
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Can I set my own bindings?
VtSkier wrote:
Help me out a little more with VECTOR here. I don't know that I can teach you vectors over the interwebs. Back when I used to teach college calculus it would take most students the better part of a semester to really "get" it. And without recourse to mathematical notation, I'm kind of limited. Sorry, but it's kind of like trying to teach skiing in a text only medium - you can only go so far before you start sounding like foot to foot. I still have one more, though, not entirely related to the present post's discussion. You said early on that TORQUE and WORK were not the same thing at all except that they shared the units used. I still have yet to puzzle out what is so much different between the two EXCEPT that direction of the FORCE applied over a length has been added to create TORQUE as opposed to WORK. The concept of horsepower was originally formulated on the basis of WORK, that is moving a FORCE over a LENGTH in a given period of time. Yet today we use TORQUE in place of WORK for formulating HORSEPOWER in a rotating engine. In any case, whether it's TORQUE or WORK, HORSEPOWER = 550 FT-POUNDS/SECOND. The difference being that you would use RPM (or more correctly RPS) for the TIME component. I'm sure there are mathematical reasons for the answers to come out the same even though the components are slightly different, it still says to me that the concepts of WORK and TORQUE while slightly different, are very closely related. This I think was the beginning of the discussion. Yes, torque and work are very closely related. In SI units, Torque is work done per radian of revolution (a radian is about 57 degrees) If you apply a torque of 1 Newton-Meter and move through an angle of one radian you have done 1 Newton-Meter or 1 Joule of work. If you apply a torque of 1 Newton-Meter and move through a complete revolution, you have done 2*pi Joules of work. If you apply a torque and nothing moves, you do no work. And if you know the torque and revolutions per minute you can calculate the rate of work (i.e. power). Hence the familiar relationship between torque, Horsepower, and rpm from automotive engineering. To sum up: Power is work per unit time Force is work per unit distance Torque is work per unit angle RPM is angle per unit time //Walt |
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#102
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Can I set my own bindings?
VtSkier wrote:
In 2) above, I'm still troubled by the wrench on the nut example. There is no component torque here, yes? Yet there is no movement of the nut until the force applied to the lever arm overcomes friction to allow the nut to move. Yes, there is component torque here. Let's use another example without vectors. Vectors are sooo last century anyway and just a figment of our imagination. Quaternions are where it's at. But anyway, Let's say we have a spindle between us. I put a torque wrench on the spindle on one side, you put a torque wrench on the other side. I apply a torque of 5 Nm on my wrench. Now we have one component of the total torque, equal to what the torque wrench reads. 5 Nm. Notice we haven't discussed motion yet, because it doesn't matter. Now you apply a torque on your wrench in the opposite direction, equal to 5 Nm. So we have two component torques which exist. Mine, 5 Nm and yours, -5 Nm. Two components of the sum. These are two *real* torques. +/-5 Nm. And there is no motion, but the torques exist. My arm gets tired because I am applying a torque, and your arm hurts becasue you are applying a torque. They just happen to balance and there is no motion because the total torque is zero. Zero motion and two torques. Torques *do* exists even in the absence of work or motion. -klaus |
#103
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Can I set my own bindings?
"klaus" wrote in message ... VtSkier wrote: In 2) above, I'm still troubled by the wrench on the nut example. There is no component torque here, yes? Yet there is no movement of the nut until the force applied to the lever arm overcomes friction to allow the nut to move. Yes, there is component torque here. Let's use another example without vectors. Vectors are sooo last century anyway and just a figment of our imagination. Quaternions are where it's at. But anyway, Let's say we have a spindle between us. I put a torque wrench on the spindle on one side, you put a torque wrench on the other side. I apply a torque of 5 Nm on my wrench. Now we have one component of the total torque, equal to what the torque wrench reads. 5 Nm. Notice we haven't discussed motion yet, because it doesn't matter. Now you apply a torque on your wrench in the opposite direction, equal to 5 Nm. So we have two component torques which exist. Mine, 5 Nm and yours, -5 Nm. Two components of the sum. These are two *real* torques. +/-5 Nm. And there is no motion, but the torques exist. My arm gets tired because I am applying a torque, and your arm hurts becasue you are applying a torque. They just happen to balance and there is no motion because the total torque is zero. Zero motion and two torques. Torques *do* exists even in the absence of work or motion. -klaus In your description there was/were initial motion to get the torque reading even though the item the torque was being applied to did not move. I believe in order to get a torque reading an applied pressure must first be used and to apply pressure some form of motion must occur first, no matter how small the distance it covers there still must be movement. I believe the question is how we get our torque measurement. The applied torque reading as with a torque wrench or the working/developed torque reading as with a running engine. JQ Dancing on the edge |
#104
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Can I set my own bindings?
JQ wrote:
In your description there was/were initial motion to get the torque reading even though the item the torque was being applied to did not move. I believe in order to get a torque reading an applied pressure must first be used and to apply pressure some form of motion must occur first, no matter how small the distance it covers there still must be movement. I believe the question is how we get our torque measurement. The applied torque reading as with a torque wrench or the working/developed torque reading as with a running engine. You mean due to the compliance of the wrench? That's pretty much beside the point, no? Use an infinitely stiff wrench. But yes. Even at the molecular level, molecules get closer together. Physics is full of "infinite" assumptions. Otherwise, they'd call it engineering. Otherwise you have to deal with material properties, quantum effects, and Heisenberg's Pet Peeve. -klaus |
#105
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Can I set my own bindings?
Walt wrote:
VtSkier wrote: Help me out a little more with VECTOR here. I don't know that I can teach you vectors over the interwebs. Back when I used to teach college calculus it would take most students the better part of a semester to really "get" it. And without recourse to mathematical notation, I'm kind of limited. Sorry, but it's kind of like trying to teach skiing in a text only medium - you can only go so far before you start sounding like foot to foot. I actually took a calculus course once. It was taught as a "pure" discipline and you were to use the rules and apply them as taught. Nowhere was there any explanation of WHY these rules were taught and WHAT the math could be used for. IF I had been told that the math was to describe motion and rate of change, I might have found a reason to actually learn the stuff. As it is, I excel in trig and geometry because I was shown practical applications from the get-go. It took two tries to pass calculus and the second time I only passed because I had taken it before and the instructor's first language was not English and he graded on a curve in a class where NO ONE had a clue. I hope your teaching was as patient and thoughtful as your explanations here have been. I still have one more, though, not entirely related to the present post's discussion. You said early on that TORQUE and WORK were not the same thing at all except that they shared the units used. I still have yet to puzzle out what is so much different between the two EXCEPT that direction of the FORCE applied over a length has been added to create TORQUE as opposed to WORK. The concept of horsepower was originally formulated on the basis of WORK, that is moving a FORCE over a LENGTH in a given period of time. Yet today we use TORQUE in place of WORK for formulating HORSEPOWER in a rotating engine. In any case, whether it's TORQUE or WORK, HORSEPOWER = 550 FT-POUNDS/SECOND. The difference being that you would use RPM (or more correctly RPS) for the TIME component. I'm sure there are mathematical reasons for the answers to come out the same even though the components are slightly different, it still says to me that the concepts of WORK and TORQUE while slightly different, are very closely related. This I think was the beginning of the discussion. Yes, torque and work are very closely related. In SI units, Torque is work done per radian of revolution (a radian is about 57 degrees) If you apply a torque of 1 Newton-Meter and move through an angle of one radian you have done 1 Newton-Meter or 1 Joule of work. If you apply a torque of 1 Newton-Meter and move through a complete revolution, you have done 2*pi Joules of work. If you apply a torque and nothing moves, you do no work. So I guess that TORQUE can be analogous to WORK when there is movement and it can be analogous to FORCE if there is no movement? And if you know the torque and revolutions per minute you can calculate the rate of work (i.e. power). Hence the familiar relationship between torque, Horsepower, and rpm from automotive engineering. To sum up: Power is work per unit time yes Force is work per unit distance no, work is force per unit distance Torque is work per unit angle Yes, but if you say it this way, you have strongly implied motion because WORK is FORCE per unit DISTANCE. Yet you and Klaus are convincing me that TORQUE can exist without movement. See my question above. See below. You can also say that TORQUE is ENERGY per unit angle. RPM is angle per unit time Yes, which is why the horsepower equation works with either work over time or torque over RPS, the angles cancel each other so the actual units match foot-lbs/second x 550 -------------------------------------------------- Actually I think I just got it here and it goes back to my thoughts on potential this and that. It's the difference between WORK and ENERGY. WORK = FORCE x DISTANCE, yes? ENERGY = FORCE applied to an object yet it doesn't move. Trouble is, we don't have two different terms to describe TORQUE with movement or without movement. http://hyperphysics.phy-astr.gsu.edu/hbase/work.html |
#106
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Can I set my own bindings?
VtSkier wrote:
Walt wrote: Ok, well I think we're making some progress To sum up: Power is work per unit time yes YES! Force is work per unit distance no, work is force per unit distance Um, no. Work = Force times distance W = F x d rearranging, F = W/d or in words, force is work per unit distance. If you apply a 1 newton force and let it act though 1 meter you get one joule. And if the force stays constant you do one joule of work for every meter you travel. i.e. energy per unit distance. Torque is work per unit angle Yes, but if you say it this way, you have strongly implied motion... Not really. It only implies that if the angle of motion is zero, there is zero work. See below. You can also say that TORQUE is ENERGY per unit angle. YES!!! Actually I think I just got it here and it goes back to my thoughts on potential this and that. It's the difference between WORK and ENERGY. There is not much difference between WORK and ENERGY. They are basically different words for the same concept. WORK = FORCE x DISTANCE, yes? yes. ENERGY = FORCE applied to an object yet it doesn't move. No, ENERGY is not the same thing as FORCE. When a FORCE acts through a distance you get ENERGY. When a TORQUE acts through an angle you get ENERGY. You need the motion to get the ENERGY, but the FORCE or the TORQUE can exist without the motion. Trouble is, we don't have two different terms to describe TORQUE with movement or without movement. We don't have it because we don't need it. //Walt |
#107
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Can I set my own bindings?
In article ,
VtSkier wrote: Walt wrote: VtSkier wrote: Help me out a little more with VECTOR here. I don't know that I can teach you vectors over the interwebs. Back when I used to teach college calculus it would take most students the better part of a semester to really "get" it. And without recourse to mathematical notation, I'm kind of limited. Sorry, but it's kind of like trying to teach skiing in a text only medium - you can only go so far before you start sounding like foot to foot. I actually took a calculus course once. It was taught as a "pure" discipline and you were to use the rules and apply them as taught. Nowhere was there any explanation of WHY these rules were taught and WHAT the math could be used for. IF I had been told that the math was to describe motion and rate of change, I might have found a reason to actually learn the stuff. As it is, I excel in trig and geometry because I was shown practical applications from the get-go. It took two tries to pass calculus and the second time I only passed because I had taken it before and the instructor's first language was not English and he graded on a curve in a class where NO ONE had a clue. I hope your teaching was as patient and thoughtful as your explanations here have been. I still have one more, though, not entirely related to the present post's discussion. You said early on that TORQUE and WORK were not the same thing at all except that they shared the units used. I still have yet to puzzle out what is so much different between the two EXCEPT that direction of the FORCE applied over a length has been added to create TORQUE as opposed to WORK. The concept of horsepower was originally formulated on the basis of WORK, that is moving a FORCE over a LENGTH in a given period of time. Yet today we use TORQUE in place of WORK for formulating HORSEPOWER in a rotating engine. In any case, whether it's TORQUE or WORK, HORSEPOWER = 550 FT-POUNDS/SECOND. The difference being that you would use RPM (or more correctly RPS) for the TIME component. I'm sure there are mathematical reasons for the answers to come out the same even though the components are slightly different, it still says to me that the concepts of WORK and TORQUE while slightly different, are very closely related. This I think was the beginning of the discussion. Yes, torque and work are very closely related. In SI units, Torque is work done per radian of revolution (a radian is about 57 degrees) If you apply a torque of 1 Newton-Meter and move through an angle of one radian you have done 1 Newton-Meter or 1 Joule of work. If you apply a torque of 1 Newton-Meter and move through a complete revolution, you have done 2*pi Joules of work. If you apply a torque and nothing moves, you do no work. So I guess that TORQUE can be analogous to WORK when there is movement and it can be analogous to FORCE if there is no movement? Sigh No. TORQUE can never be analogous to WORK. TORQUE is the rotational analog of FORCE. It does *not* require there to be any movement of the system for there to be torque, just as there doesn't need to be any movement of the system for there to be a force applied in a linear motion system. And if you know the torque and revolutions per minute you can calculate the rate of work (i.e. power). Hence the familiar relationship between torque, Horsepower, and rpm from automotive engineering. To sum up: Power is work per unit time yes Force is work per unit distance no, work is force per unit distance No. W = Fd. Work is force *times* distance, and thus Force is work/unit distance. Torque is work per unit angle Yes, but if you say it this way, you have strongly implied motion because WORK is FORCE per unit DISTANCE. Yet you and Klaus are convincing me that TORQUE can exist without movement. See my question above. No. He's implied that if there is *WORK* done then there must be *both* TORQUE and rotation or FORCE and DISPLACEMENT. See below. You can also say that TORQUE is ENERGY per unit angle. RPM is angle per unit time Yes, which is why the horsepower equation works with either work over time or torque over RPS, the angles cancel each other so the actual units match foot-lbs/second x 550 Wrong again. Horsepower isn't torque *over* RPM, it is torque *times* RPM. -------------------------------------------------- Actually I think I just got it here and it goes back to my thoughts on potential this and that. It's the difference between WORK and ENERGY. WORK = FORCE x DISTANCE, yes? ENERGY = FORCE applied to an object yet it doesn't move. No. Utterly incorrect. Place a weight on a table: the table will exert an upward force on the weight (if it didn't, gravity would continue to move the weight downward) yet no energy is expended. Trouble is, we don't have two different terms to describe TORQUE with movement or without movement. http://hyperphysics.phy-astr.gsu.edu/hbase/work.html Because there is no need for one; just as there is no need for two terms to describe force with and without movement. -- "The iPhone doesn't have a speaker phone" -- "I checked very carefully" -- "I checked Apple's web pages" -- Edwin on the iPhone and how he missed the demo of the iPhone speakerphone. |
#108
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Can I set my own bindings?
Walt wrote:
VtSkier wrote: Walt wrote: Ok, well I think we're making some progress To sum up: Power is work per unit time yes YES! Force is work per unit distance no, work is force per unit distance Um, no. Work = Force times distance W = F x d rearranging, F = W/d or in words, force is work per unit distance. OK... So work is: Work = Lbs x feet = pound-feet therefo Force = pound-feet/feet = pounds I can buy that force is work with the distance removed, but what's the point? If you apply a 1 newton force and let it act though 1 meter you get one joule. And if the force stays constant you do one joule of work for every meter you travel. i.e. energy per unit distance. Torque is work per unit angle Yes, but if you say it this way, you have strongly implied motion... Not really. It only implies that if the angle of motion is zero, there is zero work. See below. You can also say that TORQUE is ENERGY per unit angle. YES!!! Actually I think I just got it here and it goes back to my thoughts on potential this and that. It's the difference between WORK and ENERGY. There is not much difference between WORK and ENERGY. They are basically different words for the same concept. Same concept yes, in that Torque with and without movement are the same concept, which I'm just now getting. WORK = FORCE x DISTANCE, yes? yes. ENERGY = FORCE applied to an object yet it doesn't move. No, ENERGY is not the same thing as FORCE. I didn't say it was, see the URL I cited on this subject which I don't see in this reply. I did say that work and energy use the same units and that those concepts were similar. Try this again, you erased it in your reply: http://hyperphysics.phy-astr.gsu.edu/hbase/work.html When a FORCE acts through a distance, you get WORK When you apply FORCE to an object, you get ENERGY, but no WORK When you apply WORK through and angle, you TORQUE with a value greater than zero. There is movement. When you apply only ENERGY through an angle, you get TORQUE with a value of zero. There is no movement. When a FORCE acts through a distance you get ENERGY. When a TORQUE acts through an angle you get ENERGY. Again, see the above cite. You need the motion to get the ENERGY, but the FORCE or the TORQUE can exist without the motion. You are making FORCE and TORQUE synonymous again. It's not and never was. Trouble is, we don't have two different terms to describe TORQUE with movement or without movement. We don't have it because we don't need it. Maybe we don't, but it would be helpful. |
#109
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Can I set my own bindings?
Alan Baker wrote:
In article , VtSkier wrote: Walt wrote: VtSkier wrote: Help me out a little more with VECTOR here. I don't know that I can teach you vectors over the interwebs. Back when I used to teach college calculus it would take most students the better part of a semester to really "get" it. And without recourse to mathematical notation, I'm kind of limited. Sorry, but it's kind of like trying to teach skiing in a text only medium - you can only go so far before you start sounding like foot to foot. I actually took a calculus course once. It was taught as a "pure" discipline and you were to use the rules and apply them as taught. Nowhere was there any explanation of WHY these rules were taught and WHAT the math could be used for. IF I had been told that the math was to describe motion and rate of change, I might have found a reason to actually learn the stuff. As it is, I excel in trig and geometry because I was shown practical applications from the get-go. It took two tries to pass calculus and the second time I only passed because I had taken it before and the instructor's first language was not English and he graded on a curve in a class where NO ONE had a clue. I hope your teaching was as patient and thoughtful as your explanations here have been. I still have one more, though, not entirely related to the present post's discussion. You said early on that TORQUE and WORK were not the same thing at all except that they shared the units used. I still have yet to puzzle out what is so much different between the two EXCEPT that direction of the FORCE applied over a length has been added to create TORQUE as opposed to WORK. The concept of horsepower was originally formulated on the basis of WORK, that is moving a FORCE over a LENGTH in a given period of time. Yet today we use TORQUE in place of WORK for formulating HORSEPOWER in a rotating engine. In any case, whether it's TORQUE or WORK, HORSEPOWER = 550 FT-POUNDS/SECOND. The difference being that you would use RPM (or more correctly RPS) for the TIME component. I'm sure there are mathematical reasons for the answers to come out the same even though the components are slightly different, it still says to me that the concepts of WORK and TORQUE while slightly different, are very closely related. This I think was the beginning of the discussion. Yes, torque and work are very closely related. In SI units, Torque is work done per radian of revolution (a radian is about 57 degrees) If you apply a torque of 1 Newton-Meter and move through an angle of one radian you have done 1 Newton-Meter or 1 Joule of work. If you apply a torque of 1 Newton-Meter and move through a complete revolution, you have done 2*pi Joules of work. If you apply a torque and nothing moves, you do no work. So I guess that TORQUE can be analogous to WORK when there is movement and it can be analogous to FORCE if there is no movement? Sigh No. TORQUE can never be analogous to WORK. TORQUE is the rotational analog of FORCE. It does *not* require there to be any movement of the system for there to be torque, just as there doesn't need to be any movement of the system for there to be a force applied in a linear motion system. And if you know the torque and revolutions per minute you can calculate the rate of work (i.e. power). Hence the familiar relationship between torque, Horsepower, and rpm from automotive engineering. To sum up: Power is work per unit time yes Force is work per unit distance no, work is force per unit distance No. W = Fd. Work is force *times* distance, and thus Force is work/unit distance. Torque is work per unit angle Yes, but if you say it this way, you have strongly implied motion because WORK is FORCE per unit DISTANCE. Yet you and Klaus are convincing me that TORQUE can exist without movement. See my question above. No. He's implied that if there is *WORK* done then there must be *both* TORQUE and rotation or FORCE and DISPLACEMENT. See below. You can also say that TORQUE is ENERGY per unit angle. RPM is angle per unit time Yes, which is why the horsepower equation works with either work over time or torque over RPS, the angles cancel each other so the actual units match foot-lbs/second x 550 Wrong again. Horsepower isn't torque *over* RPM, it is torque *times* RPM. -------------------------------------------------- Actually I think I just got it here and it goes back to my thoughts on potential this and that. It's the difference between WORK and ENERGY. WORK = FORCE x DISTANCE, yes? ENERGY = FORCE applied to an object yet it doesn't move. No. Utterly incorrect. Place a weight on a table: the table will exert an upward force on the weight (if it didn't, gravity would continue to move the weight downward) yet no energy is expended. and there is no movement. Trouble is, we don't have two different terms to describe TORQUE with movement or without movement. http://hyperphysics.phy-astr.gsu.edu/hbase/work.html Because there is no need for one; just as there is no need for two terms to describe force with and without movement. Alan, I'm doing better here with Walt. At least he has some patience with an old fart stuck in the last century, maybe the century before. |
#110
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Can I set my own bindings?
VtSkier wrote:
Walt wrote: VtSkier wrote: ENERGY = FORCE applied to an object yet it doesn't move. No, ENERGY is not the same thing as FORCE. I didn't say it was... You see, this is why we are having trouble communicating. When I see the equals sign it means something specific to me, i.e. the things on either side of it are the same. Obviously, it means something different to you. Likewise, the terms FORCE ENERGY TORQUE etc have very specific meanings to me, but you are bandying about these terms without regard to their standard meaning in physics - that makes it rather hard to have a discussion. It's like trying to parse something like "I had my bindings waxed and now the moguls don't hurt my feet when I schuss across the hill in a parallel stem-christie wedge turn." It's hard to follow what the heck the person is on about. //walt |
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