Torque vs Energy. Same units, not the same thing

[SameSame]

Please Jolle show me Joules in SI units. No long winded explanation, just the unit of a Joule in SI units.

[Jolle]

I'm sorry I'm busy using my phone but I'll show you later a proper derivation using a computer.

Please do some reading on how a gearbox works. Just google is power conserved between gears and you will see thousands of links confirming that.

Energy has no units of seconds in it.

I'll say it one last time. Power is constant through gears and torque is what changes. Without any spinning motion of the gears no torque is transmitted and therefore the conservation of energy is not violated. As soon as the gears move POWER is transferred between gears and therefore ENERGY IS CONSERVED as you just have to multiply the power by time to get the energy.

From Wikipedia:


Confusion with newton-metre

Main article: newton metre
In angular mechanics, torque is analogous to the linear Newtonian mechanics parameter of force, moment of inertia to mass, and angle to distance. Energy is the same in both systems. Thus, although the joule has the same dimensions as the newton-metre (1 J = 1 N·m = 1 kg·m2·s−2), these units are not interchangeable: the CGPM has given the unit of energy the name "joule", but has not given the unit of torque any special name, hence the unit of torque is known as the newton-metre (N·m) - a compound name derived from its constituent parts.[5] Torque and energy are related to each other using the equation

https://en.m.wikipedia.org/wiki/Joule

[SameSame]

That is literally what I have been saying for the past hundred posts… (1 J = 1 N.m)

And I've been told the units don't check out…

[rscsr]

That is literally what I have been saying for the past hundred posts… (1 J = 1 N.m)

And I've been told the units don't check out…

In angular mechanics, torque is analogous to the linear Newtonian mechanics parameter of force, moment of inertia to mass, and angle to distance. Energy is the same in both systems. Thus, although the joule has the same dimensions as the newton-metre (1 J = 1 N·m = 1 kg·m2·s−2), these units are not interchangeable: the CGPM has given the unit of energy the name "joule", but has not given the unit of torque any special name, hence the unit of torque is known as the newton-metre (N·m) - a compound name derived from its constituent parts.[5] Torque and energy are related to each other using the equation

E = τ θ

where E is the energy, τ is the torque, and θ is the angle moved (in radians). Since radians are dimensionless, it follows that torque and energy have the same dimensions.

The use of newton-metres for torque and joules for energy is useful in helping avoid misunderstandings and miscommunications.[5]

An additional solution is to realize that joules are scalars – they are the dot product of a vector force and a vector displacement whereas torque is a vector. Torque is the cross product of a distance vector and a force vector. Drawing a traditional vector arrow over "newton-metre" in a torque resolves the ambiguity.

[SameSame]

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.

Edit: All I wanted to convey was that 1 J = 1 N.m. Not the technicality of whether they can be used interchangeably. I was told the units don't work out and how can a gearbox work if that is true.

[rscsr]

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.

Edit: All I wanted to convey was that 1 J = 1 N.m. Not the technicality of whether they can be used interchangeably. I was told the units don't work out and how can a gearbox work if that is true.

Torque is N.m an not N/m… and N.m = J so power is basically the rate at which the torque is delivered, which is perfectly in line with what FoxHound said.

Are you saying torque is energy?

Indeed I am. Think about power. rad/s (angular velocity) x N.m (Torque) = J/s. (A radian is dimensionless)

torque and energy have the same units, but since you explicitly stated that torque = energy I think it is not far fetched to think that you want to use torque and energy interchangeable.

[SameSame]

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.

Edit: All I wanted to convey was that 1 J = 1 N.m. Not the technicality of whether they can be used interchangeably. I was told the units don't work out and how can a gearbox work if that is true.

Are you saying torque is energy?

Indeed I am. Think about power. rad/s (angular velocity) x N.m (Torque) = J/s. (A radian is dimensionless)

torque and energy have the same units, but since you explicitly stated that torque = energy I think it is not far fetched to think that you want to use torque and energy interchangeable.

Last point because this is way off topic.

In the case of power, N.m is replaced by J. So no they are not interchangeable, but torque "is" energy in this case. But that's not even the point. The main point was that that relation was not true at all, let's not nit pick on technicalities that deviate from the main point of the whole discussion. I was told it was not and wanted to simply educate people that it is.

And this is my last word on the topic.

[Cold Fussion]

You may consider it nitpicking, but it is incorrect to state torque is energy. This is a technical forum (supposedly at least) so something that is so fundamental should not be glossed over.

http://s2.quickmeme.com/img/b3/b3d65e69 ... d7a5c2.jpg


I'm reading that horsepower is a (nigh on)fictitious measurement designed to give an apt description to prospective buyers as to the indication of the power.

James Watt responsible.

Torque is measurable, and a complete indicator of the rotational force.

So why would it not be plausible that a 150bhp 200nm Diesel of same mass and size to that of a 170bhp 120nm Petrol, would be quicker.
It has more rotational force, and the as Horspeower is defined from inception as thus:

To get industries to begin adopting his steam engines, Watt came up with the term horsepower so buyers could have a way of comparing his engines with more traditional power sources. One version of how Watt first calculated the meaning of horsepower starts with an early customer, a saw mill that replaced horses with a steam engine. The horses were attached to a 24-foot diameter wheel, which yields to a circumference of 75.4 feet around. Watt determined each horse's pulling force and came up with an average of 180 pounds per animal. He counted that the horses turned the wheel 144 times per hour, which is 2.4 times per minute. With a 75.4-foot path around the wheel, each horse was moving 181 feet per minute. Multiply the feet per minute (181) by the force of each horse (180) and you arrive at 32,580. Watt did the same and rounded up to an even 33,000-lbs.ft. per minute to determine the value of one, single horsepower.

http://www.hemmings.com/magazine/hmn/20 ... 18941.html
It suggests that Horsepower was designed to give indication of the power available over a timed period, in the above a minute being the timed period.

So to my mind, and without the math, it suggest exactly what the Yuasa engineer was purporting over a cold one.
The petrol can deliver it's torque quicker, but it's torque, or rotational force, is circa 40% down on the Diesel, which in turn is circa 15% down in terms of horspower.

Torque is a meaningless quantity when considering the performance of a vehicle. When the manufacturer specifies torque, this torque is measured at the flywheel. After the flywheel, the drive train has a gearbox which changes the torque at the output relative to the input (by conserving energy and not torque). Why is this important? Because once you know energy is conserved throughout the drivetrain (and thus power), and you know that Power = Torque x Angular velocity, you can see what is of most importance is power and not measured flywheel torque.

In laymans terms, the point of the gearbox is to change the road speed at which the engine is producing maximum power. If you have a 6 speed gearbox that 6 different vehicle velocities where you have maximum power. Once you understand this then it should be pretty obvious to see why a car with more power is faster than a car with less power but with more torque.

Furthermore, if you were to try and build a vehicle dynamics model, there is no way you could build a model where vehicle torque is an input of it's own right (that is without an associated engine speed to give you the required power). Consider this, a track sprinter produces more torque on the bike crank than your diesel car.

[bhall II]

Bhall It's happening again.

[mrluke]

Torque can be seen as the power of 1 revolution, bhp is the power delivered over time, the more revolutions per minute you have the more opportunities you have to increase your power over time.

[SameSame]

Hahaha that's pretty good. But the units check out. Not intuitive but yet still true.

But it just doesn't check out at all. If torque is energy, how would one apply the conservation of energy in a gearbox? I have a torque at the input shaft and a different torque at the output shaft, if torque is energy, then where did this extra come from? Perhaps the teapot floating around Venus put it there? Similarly, if radians are a dimensionless unit, then why don't we measure angular velocity in hertz? You contend that radians are a dimensionless unit but that isn't really correct.

Very interesting how quickly your tune has changed? So all of a sudden a gearbox does conserve energy?

Don't give the technical forum nonsense when you were saying stuff like this. What about the teapot and the Venus? What about a radian not being dimensionless.

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.

[Phil]

So why would it not be plausible that a 150bhp 200nm Diesel of same mass and size to that of a 170bhp 120nm Petrol, would be quicker.

Have you ever heard of gearing? And perhaps that any bhp figure is only at a particular point of a wide rev-range? To determine which car is actually quicker, depends on the gearing and how much power is available at that particular rev-range...

Simply talking about a peak figure is not very indicative. And not in F1 either, obviously, e.g. all this talk about the Merc engine having the highest peak bhp is pretty meaningless without understanding how long they can sustain it and/or how much power the engine makes at a different rev-range etc.

[SameSame]

I can't believe something so so basic as is 1 N.m = 1 J has turned into this.

[Cold Fussion]

Very interesting how quickly your tune has changed? So all of a sudden a gearbox does conserve energy?

When did I ever say otherwise?

But it just doesn't check out at all. If torque is energy, how would one apply the conservation of energy in a gearbox?

I quite clearly state that conservation of energy applies in a gearbox. If torque is energy and energy is conserved, and there's a difference of torque between input and output, how do you rationalise that energy (which for you is torque) is conserved?

[Tim.Wright]

I'm only making this one post.

So why would it not be plausible that a 150bhp 200nm Diesel of same mass and size to that of a 170bhp 120nm Petrol, would be quicker.

End of discussion...

Are you saying torque is energy?

Indeed I am. Think about power. rad/s (angular velocity) x N.m (Torque) = J/s. (A radian is dimensionless)

A shaft can be in static equilibrium under loadcase of 2 equal and opposing 100Nm torques. The torque in the shaft is 100Nm, the energy in this shaft is ZERO. Therefore torque =/= energy.

End of discussion.