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#526
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Please stop calling them apps!
On Thu, 20 Jun 2019 09:32:17 -0400, "Jonathan N. Little"
wrote: Eric Stevens wrote: On Wed, 19 Jun 2019 22:38:31 -0400, Paul wrote: Eric Stevens wrote: You have said: " Torque means precisely **** all, because depending on the revs, you can have a completely different output. ..... And all I need to know is the horsepower available. I want to know if it equates to enough to lift the mass of the car up the hill at the speed I want." There is always a sample exercise available somewhere. https://x-engineer.org/projects/vehi...ng-simulation/ "The traction force can be regarded a a 'positive' force, trying to move the vehicle forward. All the other forces, are resistant, 'negative' forces which are opposing motion, trying to slow down the vehicle." "The traction force [N] depends on the engine torque, === engaged transmission gear ratio, final drive ratio (differential), and wheel radius: Torque is what gets the job done. If the Traction Force isn't greater than the other forces, you're not moving forward. Yep. Most people don't need to have it explained to them. Spinning your wheels seems to describe this thread "app"-tly ;-) Yes, but very slowly, in a very low gear. There is not enough grip to allow the application of much power. -- Regards, Eric Stevens |
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#527
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Please stop calling them apps!
On 6/20/2019 10:18 PM, Eric Stevens wrote:
On Thu, 20 Jun 2019 09:32:17 -0400, "Jonathan N. Little" wrote: Eric Stevens wrote: On Wed, 19 Jun 2019 22:38:31 -0400, Paul wrote: Eric Stevens wrote: You have said: " Torque means precisely **** all, because depending on the revs, you can have a completely different output. ..... And all I need to know is the horsepower available. I want to know if it equates to enough to lift the mass of the car up the hill at the speed I want." There is always a sample exercise available somewhere. https://x-engineer.org/projects/vehi...ng-simulation/ "The traction force can be regarded a a 'positive' force, trying to move the vehicle forward. All the other forces, are resistant, 'negative' forces which are opposing motion, trying to slow down the vehicle." "The traction force [N] depends on the engine torque, === engaged transmission gear ratio, final drive ratio (differential), and wheel radius: Torque is what gets the job done. If the Traction Force isn't greater than the other forces, you're not moving forward. Yep. Most people don't need to have it explained to them. Spinning your wheels seems to describe this thread "app"-tly ;-) Yes, but very slowly, in a very low gear. There is not enough grip to allow the application of much power. Oh no! You said the magic word .. power! Oh .. now you're gonna be in trouble! ;-) :-) -- == Later... Ron C -- |
#528
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Please stop calling them apps!
On Thu, 20 Jun 2019 01:15:46 +0100, Eric Stevens wrote:
On Wed, 19 Jun 2019 16:48:01 +0100, "Commander Kinsey" wrote: --- overdue snip --- You think torque is relevant when considering engines, I don't. Simple enough for you? Let me help you understand the error of your ways. Consider a car about to climb a hill. The car has a mass of 1500kg The gradient is such that a the force applied in the direction of the slope to propel the car against gravity and rolling resistance is 20% of the car's weight = 0.20 x 9.807 x 1500 = 2942 Newtons. The propulsive force is applied by the driving wheels against the road. The wheels are 600mm in diameter which means that the total torque which has to be supplied to the wheels by the differential = 2942 x 0.300 = 882.6 Newton.Metres. The gears of the final drive have a reduction ratio 3.14:1 which meaans that the driveshaft input torque to the final drive is: 882.6 ------ = 281.08 Newton.Metres. 3.14 The car will not climb the hill if it cannot supply the driveshaft with at least this torque. This leaves no margin for acceleration. Question: How much power does the engine need to enable the car to climb the hill? Look how complicated your question is. Now try to work it out using a simple equation of balancing energy. I think you are fudging. If I am misjudging you, please use my example to explain it your way. I can't be bothered looking at your overly complicated explanation. Your mind must be really twisted to try to calculate things in such a longwinded way. What you are really saying is that you don't properly understand the problem. Way back in this thread Carlos correctly wrote: Actually, it is the torque which changes with the gear change. The power output is the same - except that the power curve is not linear. And you replied: The power output is not the same. Double the revs gives you double the power. Changing gear changes the revs and therefore the power. In writing that you completely failed to recognize that double the revs means double the gear reduction and twice the torque applied to the driving wheels. Since then, in spite of numerous hints, you have failed to acknowledge the role of torque in all of this. The point is that power does not enter anywhere in my examplar calculation. Nor could it without any mention of speed. You can have all the power in the world available to get you up the hill but it will be totally useless unless you have the torque at the driving wheels sufficient to overcome gravity. Its torque that gets you up the hill, not power. Power only affects the speed at which you might climb the hill, assuming you have sufficient torque to climb it at all. When you change down its to get more torque. You will only get more power if you maintain vehicle speed. If the down change forces you to halve your speed you are getting the same power as before but now you are getting more torque. You have said: " Torque means precisely **** all, because depending on the revs, you can have a completely different output. ..... And all I need to know is the horsepower available. I want to know if it equates to enough to lift the mass of the car up the hill at the speed I want." You look at the HP graph, you find the maximum power you can get out of the engine, and you decide that would be enough to lift the car up the hill at say 20mph. Is there a suitable gear for this? No? But one will make it go 15mph at maximum output, so use that. |
#529
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Please stop calling them apps!
Commander Kinsey wrote:
On Thu, 20 Jun 2019 01:15:46 +0100, Eric Stevens wrote: On Wed, 19 Jun 2019 16:48:01 +0100, "Commander Kinsey" wrote: --- overdue snip --- You think torque is relevant when considering engines, I don't. Simple enough for you? Let me help you understand the error of your ways. Consider a car about to climb a hill. The car has a mass of 1500kg The gradient is such that a the force applied in the direction of the slope to propel the car against gravity and rolling resistance is 20% of the car's weight = 0.20 x 9.807 x 1500 = 2942 Newtons. The propulsive force is applied by the driving wheels against the road. The wheels are 600mm in diameter which means that the total torque which has to be supplied to the wheels by the differential = 2942 x 0.300 = 882.6 Newton.Metres. The gears of the final drive have a reduction ratio 3.14:1 which meaans that the driveshaft input torque to the final drive is: 882.6 ------ = 281.08 Newton.Metres. 3.14 The car will not climb the hill if it cannot supply the driveshaft with at least this torque. This leaves no margin for acceleration. Question: How much power does the engine need to enable the car to climb the hill? Look how complicated your question is. Now try to work it out using a simple equation of balancing energy. I think you are fudging. If I am misjudging you, please use my example to explain it your way. I can't be bothered looking at your overly complicated explanation. Your mind must be really twisted to try to calculate things in such a longwinded way. What you are really saying is that you don't properly understand the problem. Way back in this thread Carlos correctly wrote: Actually, it is the torque which changes with the gear change. The power output is the same - except that the power curve is not linear. And you replied: The power output is not the same. Double the revs gives you double the power. Changing gear changes the revs and therefore the power. In writing that you completely failed to recognize that double the revs means double the gear reduction and twice the torque applied to the driving wheels. Since then, in spite of numerous hints, you have failed to acknowledge the role of torque in all of this. The point is that power does not enter anywhere in my examplar calculation. Nor could it without any mention of speed. You can have all the power in the world available to get you up the hill but it will be totally useless unless you have the torque at the driving wheels sufficient to overcome gravity. Its torque that gets you up the hill, not power. Power only affects the speed at which you might climb the hill, assuming you have sufficient torque to climb it at all. When you change down its to get more torque. You will only get more power if you maintain vehicle speed. If the down change forces you to halve your speed you are getting the same power as before but now you are getting more torque. You have said: " Torque means precisely **** all, because depending on the revs, you can have a completely different output. ..... And all I need to know is the horsepower available. I want to know if it equates to enough to lift the mass of the car up the hill at the speed I want." You look at the HP graph, you find the maximum power you can get out of the engine, and you decide that would be enough to lift the car up the hill at say 20mph. Is there a suitable gear for this? No? But one will make it go 15mph at maximum output, so use that. Um, it's a defining equation. The controlling term is Torque. End... of... story. You can try and weasel around it all you like. If you hold a parchment in this discipline, you're taught to think in terms of defining equations. ******* Just a thought experiment should be enough to convince you. 1) A car makes the same horsepower, each time you stomp the gas. 2) Put the car on a 7 percent slope, with the car on flat ground, about to go up the hill. 3a) Put the car in fifth gear. Let out the clutch. What happens ? The car stalls. Not sufficient torque was generated, to counter the other terms in the equation. The car refuses to roll forward. 3b) Put the car in first gear. Let out the clutch. What happens ? The car goes up the hill. In (3a) and (3b), in both cases the same horsepower was available at the engine shaft... but after the transmission is done with it, there is more torque by shifting to first gear. Also notice, that if we manage to get the car into fifth gear, shifting as we drive up that hill, eventually the force equation turns against us, and the car starts to slow down before it gets to the top. When this happens, you gear down into fourth. As fifth is "too tall a gear". This is still the torque at work! Now, being a physics graduate, what do you do ? Why, a "units check". Take the units for each term in the equation, and make sure that the output is a force (or whatever). Once we've figured out the net force, we can use Fnet=MA or whatever. The discipline that comes from doing a thousand problem sets (without copying the work of a fellow student), should be cutting in about now... Paul |
#530
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Please stop calling them apps!
On Fri, 21 Jun 2019 15:01:35 +0100, Paul wrote:
Commander Kinsey wrote: On Thu, 20 Jun 2019 01:15:46 +0100, Eric Stevens wrote: On Wed, 19 Jun 2019 16:48:01 +0100, "Commander Kinsey" wrote: --- overdue snip --- You think torque is relevant when considering engines, I don't. Simple enough for you? Let me help you understand the error of your ways. Consider a car about to climb a hill. The car has a mass of 1500kg The gradient is such that a the force applied in the direction of the slope to propel the car against gravity and rolling resistance is 20% of the car's weight = 0.20 x 9.807 x 1500 = 2942 Newtons. The propulsive force is applied by the driving wheels against the road. The wheels are 600mm in diameter which means that the total torque which has to be supplied to the wheels by the differential = 2942 x 0.300 = 882.6 Newton.Metres. The gears of the final drive have a reduction ratio 3.14:1 which meaans that the driveshaft input torque to the final drive is: 882.6 ------ = 281.08 Newton.Metres. 3.14 The car will not climb the hill if it cannot supply the driveshaft with at least this torque. This leaves no margin for acceleration. Question: How much power does the engine need to enable the car to climb the hill? Look how complicated your question is. Now try to work it out using a simple equation of balancing energy. I think you are fudging. If I am misjudging you, please use my example to explain it your way. I can't be bothered looking at your overly complicated explanation. Your mind must be really twisted to try to calculate things in such a longwinded way. What you are really saying is that you don't properly understand the problem. Way back in this thread Carlos correctly wrote: Actually, it is the torque which changes with the gear change. The power output is the same - except that the power curve is not linear. And you replied: The power output is not the same. Double the revs gives you double the power. Changing gear changes the revs and therefore the power. In writing that you completely failed to recognize that double the revs means double the gear reduction and twice the torque applied to the driving wheels. Since then, in spite of numerous hints, you have failed to acknowledge the role of torque in all of this. The point is that power does not enter anywhere in my examplar calculation. Nor could it without any mention of speed. You can have all the power in the world available to get you up the hill but it will be totally useless unless you have the torque at the driving wheels sufficient to overcome gravity. Its torque that gets you up the hill, not power. Power only affects the speed at which you might climb the hill, assuming you have sufficient torque to climb it at all. When you change down its to get more torque. You will only get more power if you maintain vehicle speed. If the down change forces you to halve your speed you are getting the same power as before but now you are getting more torque. You have said: " Torque means precisely **** all, because depending on the revs, you can have a completely different output. ..... And all I need to know is the horsepower available. I want to know if it equates to enough to lift the mass of the car up the hill at the speed I want." You look at the HP graph, you find the maximum power you can get out of the engine, and you decide that would be enough to lift the car up the hill at say 20mph. Is there a suitable gear for this? No? But one will make it go 15mph at maximum output, so use that. Um, it's a defining equation. The controlling term is Torque. End... of... story. You can try and weasel around it all you like. If you hold a parchment in this discipline, you're taught to think in terms of defining equations. ******* Just a thought experiment should be enough to convince you. 1) A car makes the same horsepower, each time you stomp the gas. 2) Put the car on a 7 percent slope, with the car on flat ground, about to go up the hill. 3a) Put the car in fifth gear. Let out the clutch. What happens ? The car stalls. Not sufficient torque was generated, to counter the other terms in the equation. The car refuses to roll forward. 3b) Put the car in first gear. Let out the clutch. What happens ? The car goes up the hill. In (3a) and (3b), in both cases the same horsepower was available at the engine shaft... but after the transmission is done with it, there is more torque by shifting to first gear. Same horsepower, but you're trying to make the car go many times further up the hill in the same time, due to the different gear ratio. Also as the revs are lower, the horsepower is probably also a lot less. I guess it's just two ways of calculating the same thing. I prefer to think in terms of energy and power. Also notice, that if we manage to get the car into fifth gear, shifting as we drive up that hill, eventually the force equation turns against us, and the car starts to slow down before it gets to the top. When this happens, you gear down into fourth. As fifth is "too tall a gear". This is still the torque at work! Now, being a physics graduate, what do you do ? Why, a "units check". Take the units for each term in the equation, and make sure that the output is a force (or whatever). Once we've figured out the net force, we can use Fnet=MA or whatever. The discipline that comes from doing a thousand problem sets (without copying the work of a fellow student), should be cutting in about now... |
#531
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Please stop calling them apps!
Commander Kinsey wrote:
Same horsepower, but you're trying to make the car go many times further up the hill in the same time, due to the different gear ratio. Also as the revs are lower, the horsepower is probably also a lot less. I guess it's just two ways of calculating the same thing. I prefer to think in terms of energy and power. I already created the scenario. I have an engine. I rev to 2000 RPM in each case. The horsepower is exactly the same in each case. The engine doesn't know what I'm about to do. I try to climb a 7% grade in my car. 1) First experiment. Fifth gear. Release the clutch. Result ? Car stalls. There is insufficient torque to overcome the forces of opposition. I cannot accelerate. 2) Second experiment. First gear. Release the clutch at 2000RPM, just like before. Result. Car go up hill. There's no bleating that the input conditions changed. All that changed was the gear ratio and the resultant amount of torque, to overcome the other forces in the force equation. Paul |
#532
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Please stop calling them apps!
On Fri, 21 Jun 2019 20:04:03 +0100, Paul wrote:
Commander Kinsey wrote: Same horsepower, but you're trying to make the car go many times further up the hill in the same time, due to the different gear ratio. Also as the revs are lower, the horsepower is probably also a lot less. I guess it's just two ways of calculating the same thing. I prefer to think in terms of energy and power. I already created the scenario. I have an engine. I rev to 2000 RPM in each case. The horsepower is exactly the same in each case. The engine doesn't know what I'm about to do. I try to climb a 7% grade in my car. 1) First experiment. Fifth gear. Release the clutch. Result ? Car stalls. There is insufficient torque to overcome the forces of opposition. I cannot accelerate. 2) Second experiment. First gear. Release the clutch at 2000RPM, just like before. Result. Car go up hill. There's no bleating that the input conditions changed. All that changed was the gear ratio and the resultant amount of torque, to overcome the other forces in the force equation. What changed was the rate of ascent, by a considerable amount - the ratio of 1st to 5th. This means that you need that ratio of HP extra to climb the hill, as you would be ascending faster. If I'm cycling up a hill, I might know (fictitious numbers follow) that my thighs can output 2kW. In a low gear I move up the hill at 5mph. In a high gear I move up the same incline at 20mph. I would need 4 times as many kW to achieve this. If I attempt the high gear, my legs will be unable to give out enough kW, and I'll come to a stop. |
#533
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Please stop calling them apps!
On Fri, 21 Jun 2019 16:34:24 +0100, "Commander Kinsey"
wrote: On Fri, 21 Jun 2019 15:01:35 +0100, Paul wrote: Commander Kinsey wrote: On Thu, 20 Jun 2019 01:15:46 +0100, Eric Stevens wrote: On Wed, 19 Jun 2019 16:48:01 +0100, "Commander Kinsey" wrote: --- overdue snip --- You think torque is relevant when considering engines, I don't. Simple enough for you? Let me help you understand the error of your ways. Consider a car about to climb a hill. The car has a mass of 1500kg The gradient is such that a the force applied in the direction of the slope to propel the car against gravity and rolling resistance is 20% of the car's weight = 0.20 x 9.807 x 1500 = 2942 Newtons. The propulsive force is applied by the driving wheels against the road. The wheels are 600mm in diameter which means that the total torque which has to be supplied to the wheels by the differential = 2942 x 0.300 = 882.6 Newton.Metres. The gears of the final drive have a reduction ratio 3.14:1 which meaans that the driveshaft input torque to the final drive is: 882.6 ------ = 281.08 Newton.Metres. 3.14 The car will not climb the hill if it cannot supply the driveshaft with at least this torque. This leaves no margin for acceleration. Question: How much power does the engine need to enable the car to climb the hill? Look how complicated your question is. Now try to work it out using a simple equation of balancing energy. I think you are fudging. If I am misjudging you, please use my example to explain it your way. I can't be bothered looking at your overly complicated explanation. Your mind must be really twisted to try to calculate things in such a longwinded way. What you are really saying is that you don't properly understand the problem. Way back in this thread Carlos correctly wrote: Actually, it is the torque which changes with the gear change. The power output is the same - except that the power curve is not linear. And you replied: The power output is not the same. Double the revs gives you double the power. Changing gear changes the revs and therefore the power. In writing that you completely failed to recognize that double the revs means double the gear reduction and twice the torque applied to the driving wheels. Since then, in spite of numerous hints, you have failed to acknowledge the role of torque in all of this. The point is that power does not enter anywhere in my examplar calculation. Nor could it without any mention of speed. You can have all the power in the world available to get you up the hill but it will be totally useless unless you have the torque at the driving wheels sufficient to overcome gravity. Its torque that gets you up the hill, not power. Power only affects the speed at which you might climb the hill, assuming you have sufficient torque to climb it at all. When you change down its to get more torque. You will only get more power if you maintain vehicle speed. If the down change forces you to halve your speed you are getting the same power as before but now you are getting more torque. You have said: " Torque means precisely **** all, because depending on the revs, you can have a completely different output. ..... And all I need to know is the horsepower available. I want to know if it equates to enough to lift the mass of the car up the hill at the speed I want." You look at the HP graph, you find the maximum power you can get out of the engine, and you decide that would be enough to lift the car up the hill at say 20mph. Is there a suitable gear for this? No? But one will make it go 15mph at maximum output, so use that. Um, it's a defining equation. The controlling term is Torque. End... of... story. You can try and weasel around it all you like. If you hold a parchment in this discipline, you're taught to think in terms of defining equations. ******* Just a thought experiment should be enough to convince you. 1) A car makes the same horsepower, each time you stomp the gas. 2) Put the car on a 7 percent slope, with the car on flat ground, about to go up the hill. 3a) Put the car in fifth gear. Let out the clutch. What happens ? The car stalls. Not sufficient torque was generated, to counter the other terms in the equation. The car refuses to roll forward. 3b) Put the car in first gear. Let out the clutch. What happens ? The car goes up the hill. In (3a) and (3b), in both cases the same horsepower was available at the engine shaft... but after the transmission is done with it, there is more torque by shifting to first gear. Same horsepower, but you're trying to make the car go many times further up the hill in the same time, due to the different gear ratio. Also as the revs are lower, the horsepower is probably also a lot less. I guess it's just two ways of calculating the same thing. I prefer to think in terms of energy and power. Neither of which are the factors deciding whether or not your car can climb the hill. Also notice, that if we manage to get the car into fifth gear, shifting as we drive up that hill, eventually the force equation turns against us, and the car starts to slow down before it gets to the top. When this happens, you gear down into fourth. As fifth is "too tall a gear". This is still the torque at work! Now, being a physics graduate, what do you do ? Why, a "units check". Take the units for each term in the equation, and make sure that the output is a force (or whatever). Once we've figured out the net force, we can use Fnet=MA or whatever. The discipline that comes from doing a thousand problem sets (without copying the work of a fellow student), should be cutting in about now... -- Regards, Eric Stevens |
#534
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Please stop calling them apps!
On Fri, 21 Jun 2019 20:47:48 +0100, "Commander Kinsey"
wrote: On Fri, 21 Jun 2019 20:04:03 +0100, Paul wrote: Commander Kinsey wrote: Same horsepower, but you're trying to make the car go many times further up the hill in the same time, due to the different gear ratio. Also as the revs are lower, the horsepower is probably also a lot less. I guess it's just two ways of calculating the same thing. I prefer to think in terms of energy and power. I already created the scenario. I have an engine. I rev to 2000 RPM in each case. The horsepower is exactly the same in each case. The engine doesn't know what I'm about to do. I try to climb a 7% grade in my car. 1) First experiment. Fifth gear. Release the clutch. Result ? Car stalls. There is insufficient torque to overcome the forces of opposition. I cannot accelerate. 2) Second experiment. First gear. Release the clutch at 2000RPM, just like before. Result. Car go up hill. There's no bleating that the input conditions changed. All that changed was the gear ratio and the resultant amount of torque, to overcome the other forces in the force equation. What changed was the rate of ascent, by a considerable amount - the ratio of 1st to 5th. This means that you need that ratio of HP extra to climb the hill, as you would be ascending faster. If I'm cycling up a hill, I might know (fictitious numbers follow) that my thighs can output 2kW. In a low gear I move up the hill at 5mph. In a high gear I move up the same incline at 20mph. I would need 4 times as many kW to achieve this. If I attempt the high gear, my legs will be unable to give out enough kW, and I'll come to a stop. You will come to a stop because you are not supplying enough torque. -- Regards, Eric Stevens |
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