Torque vs Energy. Same units, not the same thing

[DiogoBrand]

On this video there's a great explanation on why power is more important than torque for acceleration.

[godlameroso]

Why do we measure torque at the crank and not the piston? After-all isn't torque created from combustion? I guess it's not practical because of how bad combustion engines are at converting energy to work.

Torque generated by piston engines is barbaric and inefficient for the most part. Some guy thought, "Let me use an explosion to punch a rod through a tube to spin something heavy on a piece of soft metal, all the while I'll waste the energy I'm making, cooling and lubricating everything, and still have a fair bit of friction". Sure it works, after all the time, money, energy, and additional technology we've invested to develop and refine it, it better. One hare brained scheme after another to try to make it better, and it makes sense, I mean after-all the fact we keep pursuing something so inefficient by design is hare brained in it's own right. So any thought that originates from it will be tained by it's original hare brainedness.

[basti313]

My bet is the Mercedes is more powerful in both torque figures and bhp. And as the simplest definition(there's a thread on this...lots of opinions) for the relation is Power = the rate at which bhp delivers it's torque. Explained to me by a Honda technician(Yuasa racing).... A diesel has 200nm torque and can deliver that at a rate of 150bhp, versus a Petrol with 120nm torque that can deliver it at 170bhp. The diesel would be superior if the cars were of similar mass, size etc.

I think tthe main problem of this discussion about tire usage and power on the Merc is, that the max torque and the max power are not directly related to each other. The max power of the ICE is simply restricted by its fuel efficiency, while the torque is not.

Well the V6 Turbo's are pushing near 500nm Torque and around 900bhp all told(with recuperated energy).
No engine revs close to the maximum of 15k, but closer to 12k due to the fuel flow restriction.
The engine's torque is nigh on instantaneously available, as evidence from 2014 depicts, right through the rev range to 12k.

I do not think these values for power and torque are real. The MGU-K alone delivers 200Nm, so realistic values would be either 500Nm for the ICE alone or if you take MGU-K and ICE together to get the 900bhp, the torque should be much higher.

If we look at the drivability there is one rule: Keep the power output constant. That means they need the peak torque to be as high as possible at as low as possible revs.
So they deploy as much as possible electrical energy at low ICE revs to get good drivability. So on an engine which is limited on electrical energy you need to take compromises...drivability vs. speed. So the energy management is the crucial part:

Bear this in mind, because now we have the tyre dealing with this torque. The tyres are the same for everyone, and the top 3 are within about 20bhp or so(torque figures for the turbo's are hard to come by).
Would it not stand to reason that a more powerful engine would be breaking traction more easily through the tyre?

No. The engine max power has nothing to do with the tire. It is the power vs rev curve, which needs to be flat.
And the max power figures are not really reasonable: If they deploy 100% battery power to reach max speed they are comparable. But no one does, they need the battery to flatten the power output out of corners. This is the point where Ferrari seemed to shine a bit at the beginning of this season: They just deployed a bit more energy on the straight, compromising the corners.

Overall:
The max speed does not tell anything, it is strongly related to aero and deployment strategy, which can be different from team to team. If you have a powerful engine you can save energy for the corners, which saves tires and makes you accelerate like on rails...like the Mercs...

[SameSame]

Because the energy is converted from linear (in the piston) to rotational energy (in the crankshaft). I don't think it would be possible to measure torque at the piston seeing as the piston moves linearly.

[Jolle]

The force per piston is also very measurable or can be worked out from the power from an engine. I do believe that is what, when building an engine is being designed, is one of the things they are working with. But if the force on all pistons is combined in an easy to measure and compare between different engines (even the ones without pistons) what is the point?

Plus, torque in a piston engine is (to make it even more difficult) average torque, in a 4t engine, over two revolutions. If you take a one cylinder engine for instance, there is just a push for ¼ of the time, ½ nothing and ¼ "negative" push (compression).

[godlameroso]

Because the energy is converted from linear (in the piston) to rotational energy (in the crankshaft). I don't think it would be possible to measure torque at the piston seeing as the piston moves linearly.

I guess it's not practical because of how bad combustion engines are at converting energy to work.

The force per piston is also very measurable or can be worked out from the power from an engine. I do believe that is what, when building an engine is being designed, is one of the things they are working with. But if the force on all pistons is combined in an easy to measure and compare between different engines (even the ones without pistons) what is the point?

Plus, torque in a piston engine is (to make it even more difficult) average torque, in a 4t engine, over two revolutions. If you take a one cylinder engine for instance, there is just a push for ¼ of the time, ½ nothing and ¼ "negative" push (compression).

Hmm, makes you wonder how much torque is a result of the inertia in the crankshaft mass, vs the rest of the combustion process. Afterall, it's the inertia in the crank that allows a single piston 4t engine to work.

[Jolle]

Because the energy is converted from linear (in the piston) to rotational energy (in the crankshaft). I don't think it would be possible to measure torque at the piston seeing as the piston moves linearly.

I guess it's not practical because of how bad combustion engines are at converting energy to work.

The force per piston is also very measurable or can be worked out from the power from an engine. I do believe that is what, when building an engine is being designed, is one of the things they are working with. But if the force on all pistons is combined in an easy to measure and compare between different engines (even the ones without pistons) what is the point?

Plus, torque in a piston engine is (to make it even more difficult) average torque, in a 4t engine, over two revolutions. If you take a one cylinder engine for instance, there is just a push for ¼ of the time, ½ nothing and ¼ "negative" push (compression).

Hmm, makes you wonder how much torque is a result of the inertia in the crankshaft mass, vs the rest of the combustion process. Afterall, it's the inertia in the crank that allows a single piston 4t engine to work.

Inertia has no result on the torque what so ever. Please re-read about what torque and power are. When a mass is moving or spinning, without a change of direction or speed, no force is present.

The torque value of an engine is measured by calculating it from the power vs revolutions. The result therefore is always an average. The real torque would be a sinus like frequency. In engine design you can also play with this, for instance the big-bang 500cc 2t bikes from the nineties. Suddenly, with one massive (torque) push, about 4 times greater then normal and a longer period of rest, the drivability went up considerably compared to the screamer bikes with, on paper, exactly the same output.

[SameSame]

Because the energy is converted from linear (in the piston) to rotational energy (in the crankshaft). I don't think it would be possible to measure torque at the piston seeing as the piston moves linearly.

I guess it's not practical because of how bad combustion engines are at converting energy to work.

The force per piston is also very measurable or can be worked out from the power from an engine. I do believe that is what, when building an engine is being designed, is one of the things they are working with. But if the force on all pistons is combined in an easy to measure and compare between different engines (even the ones without pistons) what is the point?

Plus, torque in a piston engine is (to make it even more difficult) average torque, in a 4t engine, over two revolutions. If you take a one cylinder engine for instance, there is just a push for ¼ of the time, ½ nothing and ¼ "negative" push (compression).

Hmm, makes you wonder how much torque is a result of the inertia in the crankshaft mass, vs the rest of the combustion process. Afterall, it's the inertia in the crank that allows a single piston 4t engine to work.

Inertia has no result on the torque what so ever. Please re-read about what torque and power are. When a mass is moving or spinning, without a change of direction or speed, no force is present.

There are centripetal forces present in any rotating object....

[PhillipM]

Edit: The point is to fundamentally understand the concept. Work (which is a force (N) performed over a distance (m) is measured in Joules). So they are literally directly converted. Do not read some article and just stick by one line, rather try to understand how basic physics concepts work.

THEY ARE NOT DIRECTLY CONVERTED

Which is what everyone is trying to get past you. Work, or energy, is a force (N) applied through a distance (m) traveled, which is Joules. As you say.
Torque is a force (N) applied at a distance (m). It IS NOT a force going through a distance. If whatever you're applying the torque to doesn't move then there is no energy.

That is why the units are not interchangable. It matters how you get there.

[SameSame]

Edit: The point is to fundamentally understand the concept. Work (which is a force (N) performed over a distance (m) is measured in Joules). So they are literally directly converted. Do not read some article and just stick by one line, rather try to understand how basic physics concepts work.

THEY ARE NOT DIRECTLY CONVERTED

Which is what everyone is trying to get past you. Work, or energy, is a force (N) applied through a distance (m) traveled, which is Joules. As you say.
Torque is a force (N) applied at a distance (m). It IS NOT a force going through a distance. If whatever you're applying the torque to doesn't move then there is no energy.

That is why the units are not interchangable. It matters how you get there.

As I mentioned before I meant to say net torque (that's what I corrected Tim with). If an object has a net torque the torque will act through an angle.

Edit: Jolle did a great job of explaining it. There's no need for a long winded explanation, just that torque acting through an angle is energy.

Edit 2: Agree I was incorrect to say they are directly converted. It's by the radian amount the torque acted through.

[Jolle]

I guess it's not practical because of how bad combustion engines are at converting energy to work.



Hmm, makes you wonder how much torque is a result of the inertia in the crankshaft mass, vs the rest of the combustion process. Afterall, it's the inertia in the crank that allows a single piston 4t engine to work.

Inertia has no result on the torque what so ever. Please re-read about what torque and power are. When a mass is moving or spinning, without a change of direction or speed, no force is present.

There are centripetal forces present in any rotating object....

And there is some tension between the engineer and his wife but that has nothing to do with torque, power or inertia.

[SameSame]

Centripetal forces have everything to do with inertia… A massless object would experience no cevtripitel force

Or my sense of humor has taken a nose dive after a long day

[Jolle]

Centripetal forces have everything to do with inertia… A massless object would experience no cevtripitel force

Or my sense of humor has taken a nose dive after a long day

Again you're almost right but also wrong. A spinning mass has an inertia energy stored inside it's mass and movement. A spinning object also experience rotational force.
A roling car for instance does have inertia but not a rotational force or what kind of force whatsoever.

The centrifugal force is a result of a constant but fixed at 90% of the centreline, change of direction of the mass

[wuzak]

I never said they were interchangeable…

In power, N.m is converted to J for convinience sake…

I was also told a radian is not dimensionless…

My point was that N.m/s is expressed as J/s. Look how power is derived.

I believe this was covered before.

In calculation of power from torque we have

P= T*w

where w = angular velocity in radians per second

Torque's Nm is not "converted to J for convenience sake" in calculating power.

The torque multiplied by the angle gives the energy and then divided by the time gives power.

It can be rewritten as P = (T * a)/t

Where a = angle of rotation in radians and t = time over which the rotation occurs. Thus T * a = energy in Joules.

The radian is dimensionless.

From Wiki:

Radian describes the plane angle subtended by a circular arc as the length of the arc divided by the radius of the arc. One radian is the angle subtended at the center of a circle by an arc that is equal in length to the radius of the circle. More generally, the magnitude in radians of such a subtended angle is equal to the ratio of the arc length to the radius of the circle; that is, θ = s / r, where θ is the subtended angle in radians, s is arc length, and r is radius. Conversely, the length of the enclosed arc is equal to the radius multiplied by the magnitude of the angle in radians; that is, s = rθ.

https://en.wikipedia.org/wiki/Radian

Dimensionally speaking, a radian is [L]/[L] which is dimensionless.

[Cold Fussion]

Furthermore if torque is energy, then power would be time derivative of torque, which is absolutely not the same as power = torque * angular velocity.