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Torque...it's Power


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#101 Greg Locock

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Posted 01 April 2012 - 22:46

The key here is that the chock translates no energy to the tricycle.

Now instead of the wheel chock, imagine that you occupy the seat of the tricycle and you are using your feet on the pedals to hold the vehicle in place on the incline. After a minute or two you will start getting tired. After an hour you will be more tired still, and after several hours you will be tired indeed. By this time you may have contrived some means of arranging your foot or leg as a wedge or stop to hold the trike in place so you don't have to do all that work.


Yes, it is true that some means of supplying a force require the generation of power to maintain that force, such as a hovering helicopter, a stalled electric motor, and so on. Others do not, wheel chocks, clamped brakes, worm gears that are back driven and of the correct geometry, nails holding chairs to floors, stepladders, etc

If you died in the seat of the trike, and rigor mortis set in and your foot wedged the pedals, no muscle work would be done and the trike would remain stationary. So apparently your argument is that there is a different definition of physical work for live and dead people.







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#102 Magoo

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Posted 01 April 2012 - 23:56

If you died in the seat of the trike, and rigor mortis set in and your foot wedged the pedals, no muscle work would be done and the trike would remain stationary. So apparently your argument is that there is a different definition of physical work for live and dead people.


No, you are only missing an obvious fact: There are ways to arrest the tricycle's motion on the incline that require continued physical effort and ways that do not. It has nothing whatsoever to do with being alive or dead.

For example: Let's say you have a wooden leg, which you somehow insert through the spokes of the front wheel and wedge against the ground to hold the tricycle in place. Then you are free to go on your way with the tricycle safely fixed in place -- albeit without your prosthetic limb. You haven't invented a new class of work; you've only figured a way out of doing it.

Edited by Magoo, 01 April 2012 - 23:57.


#103 Wolf

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Posted 02 April 2012 - 00:05

And in which way does that wooden leg provide work? Let us assume, for all intents and purposes of this discussion, that laws of energy conservation hold- what energy is being used to provide this work?

#104 Greg Locock

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Posted 02 April 2012 - 02:46

OK, one last try.


We have a mass, M. We have a worm drive and an electric motor, arranged to jack M up and down. In case A the worm drive is a 50:1 traditional design. The motor can be switched on, the mass rises. When we switch the motor off, the mass remains in place, supported by the internal friction of the gear. No work is being done.

In case B we redesign the worm gear to the best of our ability, so that it can be back driven. We switch the motor on, the mass rises. If we switch the motor off, the mass falls again, so we switch the motor back on and fiddle with the current until the mass remains stationary.

The motor is consuming power, and warming the air. It is doing no work on the mass, because the mass isn't moving.

So, sometimes you have to do work to generate a stationary force, and sometimes you don't. Helicopters and stepladders.

Of course if you want to join the crazy people you can explain why a magnet can support another magnet while consuming no power, yet a coil will need an electrical supply to support the same magnet.


#105 gruntguru

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Posted 02 April 2012 - 02:59

Magoo.
"Expenditure of energy" alone does not necessarily meet the Newtonian definition of mechanical work. If you squat with your knees bent at 90 degrees, after a few minutes it might feel like your muscles are doing a lot of work but according to Newtonian mechanics they are not - they are burning energy but all of that energy is being converted to waste heat. There is no "mechanical work" being performed.

Edited by gruntguru, 02 April 2012 - 03:00.


#106 desmo

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Posted 02 April 2012 - 03:47

Lots of work done maintaining upright balance in a squat.

#107 Magoo

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Posted 02 April 2012 - 10:26

And in which way does that wooden leg provide work? Let us assume, for all intents and purposes of this discussion, that laws of energy conservation hold- what energy is being used to provide this work?


Sigh. It's a wooden leg. A. Wooden. Leg. Nobody suggested that the wooden leg performs work.


#108 gruntguru

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Posted 02 April 2012 - 10:28

. . and neither does a real leg when it is doing something that could be done by a wooden leg.

#109 johnny yuma

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Posted 03 April 2012 - 04:53

Sigh. It's a wooden leg. A. Wooden. Leg. Nobody suggested that the wooden leg performs work.

Beautiful response.Sounds like Mr Obvious replying to First Time Caller !!

#110 Wolf

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Posted 03 April 2012 - 10:29

Yes, it indeed is, but unfortunately in contradiction to his earlier post I was referring to, in which Magoo claimed that by using the wooden leg You haven't invented a new class of work; you've only figured a way out of doing it. Other than that, the reply is beautiful.

Magoo, BTW, where did you see that definition of work? I've only seen the definitions others have been posting (like Greg's explanation), and would be interested if there is a textbook or reference book using your definition...

#111 saudoso

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Posted 03 April 2012 - 11:19

QUOTE (Greg Locock @ Mar 26 2012, 18:12)
...
A book I was given at the age of 8 illustrated this in a pair of pictures. A clown on the left is attempting unsuccesfully to lift a chair that is nailed to floor, pulling upwards with all his might. A clown on the right lifts a feather from the floor. The caption, "which clown is doing more work?" At the time the answer seemed most unfair to the chap on the left, but the physics is indisputable. ...


...
More to the point, the book is erroneous in presuming that the intent of mechanical work must always be to move an object some distance. What if the chair is clown physical fitness equipment? Of course we can describe the clown's physical exertion in terms of force, work, power, and energy. We will, however, need something other than a tape measure. We can install load cells in the floor. Meanwhile, we can see that feather-lifting is an inefficient muscular conditioning system, requiring very little *work* from the user.

Imagine a world in which one set of mechanical laws governs conventional bicycles, while another applies to exercise bicycles. I find this inconvenient.


Text books are all wrong. No use resorting to those.






#112 GSpeedR

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Posted 03 April 2012 - 11:50

The classical definition of work is a transfer of mechanical energy and is applicable to rigid body mechanics. I think we are extending this definition into other domains (non-rigid mechanics, fluid, chemical, etc) and starting to argue semantics. A kid sitting on a tree branch: in the classical sense, the tree does not move and does no work. In reality, the tree will deform and it will increase strain energy relative to its previous state until the kid is removed. Is this "work"? Depends on your definition, I guess. There is a necessary transfer of energy anytime objects contact, but whether it can be called 'work' depends on the domain we are interested in.

#113 munks

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Posted 03 April 2012 - 14:27

The classical definition of work is a transfer of mechanical energy and is applicable to rigid body mechanics. I think we are extending this definition into other domains (non-rigid mechanics, fluid, chemical, etc) and starting to argue semantics. A kid sitting on a tree branch: in the classical sense, the tree does not move and does no work. In reality, the tree will deform and it will increase strain energy relative to its previous state until the kid is removed. Is this "work"? Depends on your definition, I guess. There is a necessary transfer of energy anytime objects contact, but whether it can be called 'work' depends on the domain we are interested in.


The classical definition works fine for the deformed tree (it's very similar to a damped spring). There's initially some work while moving towards the steady state, and then after that, no work!

However, I think your point is a good one with regards to something that is using a contracted muscle electrically signaled by neural matter. I don't know anything about biology so I won't even try to comment on that. But just like slipping a clutch to hold that tricycle up, there's no work being done on the tricycle itself.

#114 Wolf

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Posted 03 April 2012 - 14:48

Munks, the way I see it muscle tissue would have some analogy to springs- a muscle cannot produce force if there is no displacement from its relaxed state, so in order to develop force the muscle must have extension/contraction or whatever, and therefore is similar to spring which cannot create force (change) without displacement (change). In both cases, IMHO force created cannot be separated from work or potential energy change within the system. What that force does outside the system (whether it produces work or not) is irrelevant. Similar to the Greg's helicopter example- propeller creates upward force by imparting kinetic energy to particles in the air, and thereby consumes torque/power, but whether this force produces work in terms of helicopter movement is dependent on how it relates to helicopter weight. Hovering helicopter will e.g. use engine power to develop force equal to its weight, and that force will exert no work on the helicopter itself (were it greater than the weight its work would be expended into increasing helicopter's potential energy relative to the earth).

#115 GSpeedR

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Posted 03 April 2012 - 15:40

The classical definition works fine for the deformed tree (it's very similar to a damped spring). There's initially some work while moving towards the steady state, and then after that, no work!

However, I think your point is a good one with regards to something that is using a contracted muscle electrically signaled by neural matter. I don't know anything about biology so I won't even try to comment on that. But just like slipping a clutch to hold that tricycle up, there's no work being done on the tricycle itself.


Yep, I agree with you, though my point was more in regard to the level of detail with which we require. With enough time and resources we could probably use quantum mechanics to determine the work done in our kid-tree system. We have to make some assumptions in order to make any conclusions.


#116 gruntguru

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Posted 03 April 2012 - 23:02

Munks, the way I see it muscle tissue would have some analogy to springs- a muscle cannot produce force if there is no displacement from its relaxed state, so in order to develop force the muscle must have extension/contraction or whatever, and therefore is similar to spring which cannot create force (change) without displacement (change). In both cases, IMHO force created cannot be separated from work or potential energy change within the system. What that force does outside the system (whether it produces work or not) is irrelevant.

Why?
It depends entirely on where the system boundary has been defined eg - weightlifter attempts to raise a heavy weight. Question. How much work does he perform on the weight? Assume the weight to be a rigid body.

The system should be defined as the weight itself. When the lifter attempts the lift, the amount of work done will be the force applied times distance moved along the line of the force. If he fails to move the weight, the work done will be zero regardless of how much force he exerts. Sure his muscles might waste a lot of energy contracting, probably performing significant work on other parts of his body but for the pupose of answering the original question, all this is irrelevant.

#117 Greg Locock

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Posted 03 April 2012 - 23:13

Yup, the hovering helicopter is undoubtedly doing work, it just isn't doing any work on the man's mass in the earth's gravitational field. It is doing a great deal of work on the surrounding air, but that is not the purpose of the experiment. The stepladder is doing no work on the man's mass in the gravitational field, once he is stationary.



#118 Wolf

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Posted 03 April 2012 - 23:47

GG- we're in agreement as far as I can see... I was merely trying to explain that confusion which seems to be about 'producing work' and 'working-out'- and moreover that particular point about muscles (which I hope we don't disagree on). Trying to lift the weight, lifters muscles will use chemical energy to produce actual work (it will be actual 'work-out' similar to 'pushing the wall'), but the force produced by that work will be insufficient to produce work on weight itself. Basically, the net effect of work produced by the muscles will be with zero efficiency. (That post was merely trying to illustrate Greg's earlier post about using work/power to produce a force that has no displacement and therefore produces no work.)

I'm glad noone confused matters even more by introducing friction... :lol:

#119 Greg Locock

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Posted 04 April 2012 - 02:17

ah well if we take friction out of the equation then a rotor with an infinite wingspan and finite self weight would require no power to drive it, so we have closed the loop between helicopters and stepladders.



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#120 bigleagueslider

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Posted 05 April 2012 - 01:18

ah well if we take friction out of the equation then a rotor with an infinite wingspan and finite self weight would require no power to drive it, so we have closed the loop between helicopters and stepladders.


Greg Locock-

Here's a video that provides the perfect demonstration of helicopter rotors and the principle of transfer of momentum:

Science can be a harsh mistress. :eek:

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#121 Kelpiecross

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Posted 05 April 2012 - 03:20

ah well if we take friction out of the equation then a rotor with an infinite wingspan and finite self weight would require no power to drive it, so we have closed the loop between helicopters and stepladders.


For something to hover - that is; not increasing its gravitational potential energy - no work needs to be done.
A hovering helium-filled balloon does no work.

Nobody seems to have mentioned the example of an automatic car held on its brakes while the engine is at WOT at the stall speed of the auto - the engine could well be producing 100 horsepower or so but doing no work on the car.

Maybe this debate should use "frames of reference". In the car examole above the FOR of the engine and gearbox, a lot of power is being expended. In the overall FOR of the car, there is no work being done.

#122 Tony Matthews

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Posted 05 April 2012 - 07:42

a lot of power is being expended............. there is no work being done.

It happens quite a lot in the building industry.

#123 hogits2

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Posted 05 April 2012 - 08:47

It happens quite a lot in the building industry.


and on forums......

Edited by hogits2, 05 April 2012 - 08:48.


#124 Tony Matthews

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Posted 05 April 2012 - 11:15

:lol:

#125 GSpeedR

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Posted 05 April 2012 - 11:51

Maybe this debate should use "frames of reference". In the car examole above the FOR of the engine and gearbox, a lot of power is being expended. In the overall FOR of the car, there is no work being done.


I think this is the issue. People are not not using the same 'system' to calculate energy/work transfer.


#126 Canuck

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Posted 06 April 2012 - 00:02

Does that mean that when I park my vehicle in the same place at night after work, as it was in the morning before work, that technically no work has been done?


#127 Magoo

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Posted 06 April 2012 - 09:57

Many of us have seen the cartoon of the two clowns, one lifting a feather and the other pulling on a chair nailed to the floor. The idea is to illustrate the simplified concept of work as force times displacement. It's not that the cartoon is wrong; it does have its point in a theoretical, textbook, abstract sort of way. However, if one has much practical experience in the world of mechanics, the cartoon depiction quickly unravels.

First, if a feather weighs .2 to .4 grams, the clown will have to carry it to the city limits and back before any significant amount of work -- say, a single newton-meter -- has been performed. With all due respect to the cartoonist, lifting a feather is an infinitesimal quantity of work -- not many laboratory instruments are capable of usefully measuring it.

But in regard to the clown with the chair, we know that a grown man pulling on a common chair is more than capable of bending (if not breaking) it all over the place; that the typical house floor is far from infinitely rigid, and that nails in wood have almost zero tensile capacity. If work is force times displacement and an adult human is pulling on a chair at full strength, a significant amount of work is being performed -- orders of magnitude more work than the clown with the feather.

#128 Magoo

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Posted 06 April 2012 - 10:28

Nobody seems to have mentioned the example of an automatic car held on its brakes while the engine is at WOT at the stall speed of the auto - the engine could well be producing 100 horsepower or so but doing no work on the car.

Maybe this debate should use "frames of reference". In the car examole above the FOR of the engine and gearbox, a lot of power is being expended. In the overall FOR of the car, there is no work being done.


It's one thing to say the engine is performing no work "on the car," whatever that means in regard to a "frame of reference" or within the bounds of a mechanical system, but it is inane to claim the engine isn't performing any work. It's performing a whole bunch of work on the torque converter. In my opinion, the torque converter is part of the car. So when you say the engine isn't performing any work "on the car," what do you mean exactly?

In the real world, when force is applied over time and/or distance, work of some form is generally the result. Systems purporting to represent zero work are more generally bullshit scenarios of the textbook variety. Do we honestly believe that a hovering helicopter is performing no work? Really?

#129 saudoso

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Posted 06 April 2012 - 11:48

The only final result of such effort is heat being released to the environment.

#130 Kelpiecross

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Posted 06 April 2012 - 13:29

It's one thing to say the engine is performing no work "on the car," whatever that means in regard to a "frame of reference" or within the bounds of a mechanical system, but it is inane to claim the engine isn't performing any work. It's performing a whole bunch of work on the torque converter. In my opinion, the torque converter is part of the car. So when you say the engine isn't performing any work "on the car," what do you mean exactly?

In the real world, when force is applied over time and/or distance, work of some form is generally the result. Systems purporting to represent zero work are more generally bullshit scenarios of the textbook variety. Do we honestly believe that a hovering helicopter is performing no work? Really?


I meant that the engine is not doing work in the sense that it is accelerating the car, causing it to climb hills, overcome rolling and air resistance etc.
Actually I think you probably are correct about work etc. The engine in the car being held on the brakes is performing work on the car - the 100HP or so is heating the car (and its surroundings) up via the torque converter, radiator, exhaust etc.

Much of your previous argument seems to involve muscle power holding various objects stationary on slopes etc. Certainly there is work being done by the muscle. Here the work doesn't involve force acting over a distance but chemical energy, glucose being converted by the cells into energy, presumably if it is not converted into mechanical work (moving the tricycle up the ramp) it is converted into heat. Nevertheless the production of heat over time can be expressed as power as correctly as if the energy went into raising something against gravity or accelerating it. But in the FOR of the tricycle itself no work is being done.

So generally speaking I think that you are correct in what you say; work and power are developed by a muscle producing a force against a non-moving object. And the power being produced (if only as heat) is just as real as the power an engine produces.

However you also state (in post 60) that mechanical work need not involve force acting over a distance - the definition of mechanical work is exactly that - force acting over a distance. Work (alone) may not need force acting over a distance - but mechanical work does by definition.

Maybe that is at the basis of this debate - mechanical work (and power) must involve force times distance; other types of work and power (chemical reactions etc.) don't involve work times distance.

Sorry about the excessive rambling but I am trying to get the whole idea straight in my head.



#131 hogits2

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Posted 06 April 2012 - 14:20

Just to add to this little tapestry....

Some confusion may be due to varying US & UK definitions of torque. UK torque can be applied to a stationary shaft whereas US mech engineering applies to a moving shaft.

I hope this helps to drag things out a bit further.

And another thing - can a hobby be described as work?

#132 Tony Matthews

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Posted 06 April 2012 - 14:42

can a hobby be described as work?

Only if it moves...

#133 hogits2

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Posted 06 April 2012 - 15:09

Only if it moves...

... one to penury, elation, Scunthorpe etc. ?

#134 desmo

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Posted 06 April 2012 - 15:09

A hobby is work without money moving to the person performing it.

#135 hogits2

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Posted 06 April 2012 - 15:17

A hobby is work without money moving to the person performing it.


A bit like turning money into heat by going motor racing.

#136 gruntguru

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Posted 06 April 2012 - 23:24

Some confusion may be due to varying US & UK definitions of torque. UK torque can be applied to a stationary shaft whereas US mech engineering applies to a moving shaft.

No. The engineering definition of torque is universal.

#137 gruntguru

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Posted 06 April 2012 - 23:40

Does that mean that when I park my vehicle in the same place at night after work, as it was in the morning before work, that technically no work has been done?

Yes. At the end of the day, all the fuel consumed ended up as heat in the atmosphere so the total nett work done ON THE CAR is zero.

#138 Magoo

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Posted 06 April 2012 - 23:43

The only final result of such effort is heat being released to the environment.


Really? I think it takes a lot of *work* to rotate a turbine through ~10W hydraulic oil at several thousand rpm. Imagine that instead of an engine, you are turning the converter by hand with a crank. You don't think you'd be performing work?

The absorption unit on a Superflow dyno is a water brake, i.e. hydraulic turbine. Do we mean to say that an engine on a dyno is not really performing work? What is the engine producing? Some kind of fake or simulated work?


#139 gruntguru

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Posted 07 April 2012 - 00:25

Many of us have seen the cartoon of the two clowns, one lifting a feather and the other pulling on a chair nailed to the floor. The idea is to illustrate the simplified concept of work as force times displacement. It's not that the cartoon is wrong; it does have its point in a theoretical, textbook, abstract sort of way. However, if one has much practical experience in the world of mechanics, the cartoon depiction quickly unravels.

First, if a feather weighs .2 to .4 grams, the clown will have to carry it to the city limits and back before any significant amount of work -- say, a single newton-meter -- has been performed. With all due respect to the cartoonist, lifting a feather is an infinitesimal quantity of work -- not many laboratory instruments are capable of usefully measuring it.

But in regard to the clown with the chair, we know that a grown man pulling on a common chair is more than capable of bending (if not breaking) it all over the place; that the typical house floor is far from infinitely rigid, and that nails in wood have almost zero tensile capacity. If work is force times displacement and an adult human is pulling on a chair at full strength, a significant amount of work is being performed -- orders of magnitude more work than the clown with the feather.

There is nothing abstract about Newtonian mechanics. The definition of "work" is very clear and unambiguous. Ambiguity can arise if the wording is poorly chosen but not if we stick to a recognised format eg

"The quantity of work performed by "A" on "B"" or
"The nett work performed by "X""

So if we want to know "the work done BY the clown ON the chair", we need to look at the interface between the clown and the chair ie the contact point. How much force is applied through that point and how far does that point move along the line of the force. No movement? No work

If the clown is grunting and his face is changing colour, there is probably some energy being expended but no work is being done on the chair.

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#140 desmo

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Posted 07 April 2012 - 00:48

There is always movement where force is applied.

#141 bigleagueslider

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Posted 07 April 2012 - 01:24

Really? I think it takes a lot of *work* to rotate a turbine through ~10W hydraulic oil at several thousand rpm. Imagine that instead of an engine, you are turning the converter by hand with a crank. You don't think you'd be performing work?

The absorption unit on a Superflow dyno is a water brake, i.e. hydraulic turbine. Do we mean to say that an engine on a dyno is not really performing work? What is the engine producing? Some kind of fake or simulated work?


Magoo,

Technically, it does not take "work" to drive that turbine through the oil, it takes "energy". The hydraulic turbine has kinetic energy, and that kinetic energy is converted to thermal energy in the fluid mass via the mechanism of viscous shear.

Of course, the whole discussion is mostly semantics. A recip piston IC engine is simply a device that converts the chemical energy in the fuel first into thermal energy, and then into kinetic energy in the crankshaft. The term "work" is also a bit confusing. An IC engine driving a generator which charges a battery, is doing "work". But the "work" done only results in the crank energy being stored as chemical molecular bonds in the battery materials. Nothing really moves, but work is done.

Very entertaining topic.
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#142 Canuck

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Posted 07 April 2012 - 02:15

Yes. At the end of the day, all the fuel consumed ended up as heat in the atmosphere so the total nett work done ON THE CAR is zero.

Ah, good. Thus the only motorsports that require the engine to do work are rally and drag racing as most others start and finish in the same place. And these guys keep claiming to be the pinnacle of racing. Phhht.

#143 gruntguru

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Posted 07 April 2012 - 02:24

There is certainly work being done when an engine drives a dyno. For rotating engines it begins as rotational "work" so we are considering torque x angle rather than force x displacement. In the case of a water-brake absorber we can look inside and see displacement of the impeller blades and force applied to the water so there is linear work ocurring evem though it is going around in circles. Ultimately, the work energy is converted to heat in the water which must be replaced with cooler water to maintain thermal equilibrium. The water-brake absorber is generally viewed as a "system" or black-box in which rotary work from the engine is converted into heat energy. Most dyno absorbers fall into this category where work is converted to heat. One exception is the AC or DC electric dynamometer where the work is converted into useful energy (electricity) and often re-injected into the electricity grid.



#144 gruntguru

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Posted 07 April 2012 - 02:28

Ah, good. Thus the only motorsports that require the engine to do work are rally and drag racing as most others start and finish in the same place. And these guys keep claiming to be the pinnacle of racing. Phhht.

Even those have a nett work to the car of zero once the car is stopped. But hillclimbing - even when the car stops, if it is at a higher altitude than the start line, it has gained some potential energy, and the fuel used was not all wasted. :)

Now if they just left all the cars at the top of the hill. :)

#145 Dmitriy_Guller

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Posted 07 April 2012 - 07:36

Yes. At the end of the day, all the fuel consumed ended up as heat in the atmosphere so the total nett work done ON THE CAR is zero.

Is that actually true? It's been years since the last torque debate, so I'm rusty on my physics, but I thought that work was defined as the line integral in the most basic and unsimplified form. That implies that if you go around in circles, and the force applied is always in the same direction as the direction of travel, you actually do perform nonzero work, even if your endpoint is the same as the starting point.

#146 gruntguru

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Posted 07 April 2012 - 08:18

Hi Dmitriy. Its the old frame-of-reference thing again.

If a car does a round trip back to its starting location, the nett work on the car from ALL sources is zero.

The work done on the car by the drivetrain will be some positive number but this will be balanced by the work done on the car by the braking system, air resistance, tyre resistance and other parasitic losses (all negative numbers). This has to be the case if the car has returned to its original energy state.

I have ignored heat energy and chemical energy stored in the car. Clearly the hot parts of the car will cool over time and the lower fuel level in the tank is an indication of how much heat energy was transfered to the environment as a result of the round trip.

Edited by gruntguru, 07 April 2012 - 08:18.


#147 Dmitriy_Guller

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Posted 07 April 2012 - 08:36

Hi Dmitriy. Its the old frame-of-reference thing again.

If a car does a round trip back to its starting location, the nett work on the car from ALL sources is zero.

The work done on the car by the drivetrain will be some positive number but this will be balanced by the work done on the car by the braking system, air resistance, tyre resistance and other parasitic losses (all negative numbers). This has to be the case if the car has returned to its original energy state.

I have ignored heat energy and chemical energy stored in the car. Clearly the hot parts of the car will cool over time and the lower fuel level in the tank is an indication of how much heat energy was transfered to the environment as a result of the round trip.

Ok, makes sense.

#148 Magoo

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Posted 07 April 2012 - 10:26

Just to add to this little tapestry....

Some confusion may be due to varying US & UK definitions of torque. UK torque can be applied to a stationary shaft whereas US mech engineering applies to a moving shaft.


No, there is only one definition of torque the world over and it applies to both rotating and stationary bodies. And shafts. In the case of torque output in machines it can seem complicated but the basics don't change.

This reminds me.... wandering off topic but it is useful info, unlike much of the gibbering in this thread: Click-type torque wrenches require the fastener to be moving to produce an accurate value. If the fastener isn't turning, the click doesn't mean anything. Thus the common mechanic's practice of going around the torquing pattern one more time and getting one more click doesn't accomplish a thing and in fact can produce over-tightening.

#149 MatsNorway

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Posted 07 April 2012 - 11:25

There are at least three common torque wrenches around. Leaf spring who does not need to be tuned back to zero after use, and normal stretching spring. (what is the official name of it?)

then there is the one with just a needle and a gauge. No click for the dummy to wait for.

Main reason i suspect for your claims is due to static friction.

This can be removed or at least reduced with lubricants. This also allows the screw/bolt to hold more force in a simple stretch test. Mostly due to less twisting forces. Issue then is vibrations. Loctite fixes both.

Haven`t we discussed this before?

#150 Wolf

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Posted 07 April 2012 - 12:22

GruntGuru- I'm not sure you're entirely right... I'd say Dmitriy's interpretation would be about right- on a return leg work is produced as well when the car is accelerating, which also reflects on your energy balance- fuel consumed is not only wasted in heat but to do the work on accelerating and moving at constant speed on the whole trip. Another point I'd like to make is that you've lumped all forces working against the direction of movement (negative) together as 'being done on the car'- there would be a case to argue that braking should be an exception (while the effect is negative on the car, the positive work is needed to achieve that, on part of driver or car itself)...