Torque and RPM relation

[Just_a_fan]

This thread is a headache lol.

If torque is more fundamental, then why does an engine need fuel?
and why would the fuel energy content matter?

Power gives the capacity to create a torque. You can create torque by harnessing power. However It doesn't work the other way round. You require energy input for any form of motion.

You get both power and torque by harnessing energy. The energy comes from the fuel. How you tune the engine determines how much power/torque you get and when. The drive train determines how you make use of it.

[strad]

you can't measure torque of a running engine directly

What do you think an engine dyno does? ..darn sure is running. Ever scatter an engine on a dyno? big bang fer sure.

[Ciro Pabón]

It´s not true that torque comes from power which in turn comes from a magical thing called energy.

All those are measurements of how things behave.

We make those measures through estimations of variations.

For example, the average rate of variation in position trough time is called speed.

The average rate of variation in speed is called acceleration.

The rate of variation in acceleration is the work or energy.Torque is a kind of work, only the displacement is not lineal but rotational (yeah, I know that´s a simplification, but it´s a good one).

The rate of variation of work is the power.

All those are ideas, abstractions. The real things are made of bosons and fermions and they communicate through gluons. There is nothing else.

The tendency to give reality to abstractions is very strong. This doesn't mean they exist. For example, many persons believe that the fact that the Earh turns around the Sun means there is an invisible force that magically emanate from the Sun, moves through empty space and it`s what actually makes the Earth revolve around the Sun.

That´s not true: simply put, there are no ¨invisible¨ forces that jump through empty space. There has to be an interchange of gluons for bosons and fermions to change their inertia.

Same happens with power, torque and rpm. All you can say is that torque and rpm together allow you to measure a rate of change in the work done by the engine and that you call that energy or power. Not any of them ¨comes¨ from the other.

In the same way you cannot say that the fact that you are measuring the speed of your car with an speedometer means that is the needle of the speedometer what makes the car move. The needle is only measuring an abstraction, is not creating anything, and much less the movement of the car.

In the same way the car or the engine has a property you have defined and called energy but it doesn't means the car moves because of the ¨energy¨ that is in the gasoline. The molecules of the gasoline oxidizing is what pushes the surfaces of the pistons, not a magical measurement of an abstraction.

I wonder why it´s so hard to explain physics to people after they study Newtonian mechanics.

Many professors attribute that difficulty to the idea of Newton of invisible forces (which came from his alchemist training, btw): in the end he was forced to abandon the concept of forces having a reality of their own and he explained that the rules he devised simply help you to explain the future behaviour of objects, not the true interactions between the Sun and the Earth, which, as far as we know, are caused by interchange of gravitons. As Newton said: hypothesis non fingo.

Frankly, I was as confused as I see many colleagues and forum friends in this thread until the previous explanation made everything very simple.

[gruntguru]

The rate of variation in acceleration is the work or energy.Torque is a kind of work, only the displacement is not lineal but rotational (yeah, I know that´s a simplification, but it´s a good one).

No No No No No.

The rate of change (time derivative) of acceleration is a thing called "jerk". No that's not a joke.

Torque is not a kind of work. It is very similar to force (a rotational version).

No need to consider gravity as anything other than an invisible force (even Einstein didn't get beyond that) especially before you even understand Newtonian mechanics.

[xpensive]

...
The rate of variation in acceleration is the work or energy.Torque is a kind of work, only the displacement is not lineal but rotational (yeah, I know that´s a simplification, but it´s a good one).
...

Good Lord Ciro, have you been communicating with WhiteBlue lately, you can hardly get it more wrong than the above?

There is more, but let's leave it there.

It is sad to notice a former moderator confusing simple Newtonian mechanics with home made ideas, very sad indeed.

[xpensive]

...
I wonder why it´s so hard to explain physics to people after they study Newtonian mechanics.
...

And here it comes, the school-of-life approach, I'm not so certain you will gather many supporters with a cheap shot like that.

[bhall II]

Given the frequency with which this topic surfaces, and how most folks seem to explain their rationale for defining torque and power in certain, distinct ways, I wonder if we're all talking about the same thing, just with different words. (Save for those of use who insist torque is energy, of course.)

In my terms, I think of torque as useful strength, and I think of power as a reflection of the rate in which that strength can be applied. That inevitably means a high-torque/low-RPM engine that makes X-horsepower is effectively identical to a low-torque/high-RPM engine that also makes X-horsepower; they just go about their bidness in different ways.

And I do think it's valid to say that torque is a kind of work, because it's the kind of work done by a reciprocating engine, similar to how thrust is the kind of work done by a jet engine. At the end of the day, though, the rate those respective kinds of work are applied is, and will always be, power, which is all that really matters for most folks.

EDIT: I also think it's equally valid for someone to insist that these things be defined with precise terminology, because that terminology exists and has for a very, very long time. In other words, there's no rational debate to be had here; this thing has already been decided. Yet, one has to understand that a lot of us unedumakated heathens, myself included, don't always understand those terms unless they're dumbed down a bit. I think accessibility is important.

[xpensive]

...
And I do think it's valid to say that torque is a kind of work, because it's the kind of work...
...

Perhaps you should form a club, yourself, WB and Ciro?

Try and think this way MrB;

Linear;
- Energy (Ws or J) is Force (N) times Distance (m)
- Power (W) is Force (N) times Speed (m/s)

Angular;
- Energy (Ws or J) is Torque (Nm) times Angular distance (radians)
- Power (W) is Torque (Nm) times Angular speed (radians/s.)

[hollus]

Torque is a kind of force, and it only produces work when it becomes associated with movement (direction caveats apply). And I am 120% sure that Ciro and Ball know that. But putting abstract conceps into words is so difficult, especially in a hot august day!
In case the original poster hasn't been scared by now, think of a bicycle. You are the engine and your legs always turn at more or less the same RPM. But think of what happens as you go throught the gears, both if accelerating and at constant speed...

[bhall II]

Perhaps you should form a club, yourself, WB and Ciro?

[...]

It was funnier when you said we should get a room. At least, my reply to that was funnier.

Try to see the "kind of work" statement for what it attempts to convey instead of letting the terminology stop you in your tracks. The work performed by a reciprocating engine is torque, just like the work performed by a jet, or a rocket, is thrust. In each case, power is a measure of how quickly those different kinds of work can be brought to bear in their respective ways.

Admittedly, the statement is colloquial as hell. But, I think it gets the idea across.

EDIT: Would it better to say that torque is the nature of the work performed by a reciprocating engine?

[wuzak]

The work performed by a reciprocating engine is getting something to move. Like a car.

Thrust can be thought of as a linear equivalent of torque, but it is also not work. Thrust is a force, work is a form of energy.

Work = Force x Distance.

[bhall II]

The work performed by a jet engine is also getting something to move, just in a different way.

Again, I'm pretty sure most folks understand the relationship between torque and power; it's just difficult to convey such an understanding in a way that everyone can recognize.

[xpensive]

...
The work performed by a reciprocating engine is torque,...
...

You're only making it worse.

https://www.youtube.com/watch?v=DbO5h8Ctfs8

Perhaps the problem is to comprehend that "Work" and "Energy" is the same?

[bhall II]

Once more - and with feeling - try to look for the idea instead of the wording.

I'm not suggesting that torque is synonymous with work, and I'm sure as --- not suggesting that torque is energy.

What I'm saying is that the work, the job, the duty, the purpose, the function, the responsibility, or the modas operandi, etc, of a reciprocating engine is to create torque in much the same way the work, the job, the duty, the purpose, the function, the responsibility, or the modas operandi, etc, of a jet engine is to create thrust.

[gruntguru]

Ohhh THAT work!

We were talking about "NEWTONIAN" work.