Torque vs Energy. Same units, not the same thing

[mcdenife]

SameSame wrote

The fuel is combusted and ENERGY is released from it. So although it's not good practice to use the terms interchangeably, torque is energy. SI units do not lie.

No, but derived units should be used with care. quick question, is force also energy? Your premise seems to be that because energy is expended exerting a force, then force is energy. Regardless of the units, torque is not energy nor is used interchangeably with energy.

[jz11]

Everywhere I've looked has described torque as 'rotational force'.
If that is easily dismissed as "not energy" I'd like to know why.

Let's go back to where all of this energy started… The fuel is combusted and ENERGY is released from it. From there, the piston moves and thanks to some clever kinematics a crank shaft is rotated. The torque in the crank shaft is just the mechanical form of the energy that the fuel produced. So although it's not good practice to use the terms interchangeably, torque is energy. SI units do not lie.

Energy is always conserved, whether it is in the kinetic/electrical/chemical/potential forms.

Mercedes seem to be doing the best job of using their available energy in all the right places

Nicely woven into the topic batman!

So for the purpose of the discussion, and not the wider context.... A V6 Turbo producing 500nm torque and reving to 12k, with linear deliver from the worst to best engines at a rate of around 870 to 900bhp, is this fuel-energy-converted-torque at a wide enough discrepancy to be a differentiator in tyre usage?

At this level of torque, for a car weighing it 700kgs, with the tyres provided, breaking traction is inevitable for every car.
Just a case of when. So I'd say the engine itself is not a good explanation.
Gearing and mapping comes into this equation, but teams will converge on the ideal settings as choice is limited, particularly with gearing.

torque is not energy, it is an energy potential, and starts to gain meaning (in energy context), when you add rpm to your torque, else it is only relevant to clutch or other drive train design engineers

and "torque delivery" (from drive train design context) has nothing to do with tire life, what you talk here about is "power delivery" and power delivery is torque+rpm

in ideal world driver would like to have linear response to the throttle pedal, meaning - you instantly get certain % of max available power when you press throttle a certain %, in real life this doesn't happen unless you're driving an EV, and this is where "power delivery" comes in, how well the power unit management is designed and how well the driver can extract max power of the engine and put it all down on tarmac, this is probably why less powerful renault v8 was overall better (discounting special mapping exploits, hot blowing etc) than merc v8, and adding turbo, kers and hers complicates this, and this is very easy to see when you look at corner exits - mercs are very steady while ferarris are moving around - because it is/was (especially at beginning of this current turbo era) difficult for the driver to get the max amount of power out of the engine while driving on the edge of the grip level - sudden power output spikes (or losses) will unsettle the car and might even brake traction - the worse it is - the less confidence the driver has in the car - the further away he is from the max potential

and this uneven power delivery coincidentally is causing additional tire wear, so a more powerful and "fluid" "merc engine package" can be more gentle to the tires than a ferrari power unit

this is why it isn't appropriate to talk about "torque delivery" in the context of tire management

[SameSame]

SameSame wrote

The fuel is combusted and ENERGY is released from it. So although it's not good practice to use the terms interchangeably, torque is energy. SI units do not lie.

No, but derived units should be used with care. quick question, is force also energy? Your premise seems to be that because energy is expended exerting a force, then force is energy. Regardless of the units, torque is not energy nor is used interchangeably with energy.

A force acting over a distance is Work (measured in Joules)

Think of the boundary work done by a piston

Force is NOT energy.

[bhall II]

At this level of torque, for a car weighing it 700kgs, with the tyres provided, breaking traction is inevitable for every car.
Just a case of when. So I'd say the engine itself is not a good explanation.
Gearing and mapping comes into this equation, but teams will converge on the ideal settings as choice is limited, particularly with gearing.

Insofar as the ability of a car to break traction due to wheelspin is concerned, torque is irrelevant, because properly geared cars of equal horsepower, regardless of torque, will have identical power at the drive wheels...



In terms of driveability, the wider power band afforded by a high-torque engine will typically offer the driver more precise control over torque demand, because, all else being equal, throttle response will be more gradual, whereas a highly-strung, low-torque engine will be tend to be "peaky."

It's the same thing as a longer first gear; you're flattening the power curve...



EDIT: I'll post this again, as it seems to have been missed before, and I'd love for the "what is torque" part of the discussion to end. According to the International Bureau of Weights and Measures...

For convenience, certain coherent derived units have been given special names and symbols. There are 22 such units, as listed in Table 3. These special names and symbols may themselves be used in combination with the names and symbols for base units and for other derived units to express the units of other derived quantities. Some examples are given in Table 4. The special names and symbols are simply a compact form for the expression of combinations of base units that are used frequently, but in many cases they also serve to remind the reader of the quantity involved. The SI prefixes may be used with any of the special names and symbols, but when this is done the resulting unit will no longer be coherent.

Among these names and symbols the last four entries in Table 3 are of particular note since they were adopted by the 15th CGPM (1975, Resolutions 8 and 9), the 16th CGPM (1979, Resolution 5) and the 21st CGPM (1999, Resolution 12) specifically with a view to safeguarding human health.

In both Tables 3 and 4 the final column shows how the SI units concerned may be expressed in terms of SI base units. In this column factors such as m^0, kg^0, etc., which are all equal to 1, are not shown explicitly.

The values of several different quantities may be expressed using the same name and symbol for the SI unit. Thus for the quantity heat capacity as well as the quantity entropy, the SI unit is the joule per kelvin. Similarly for the base quantity electric current as well as the derived quantity magnetomotive force, the SI unit is the ampere. It is therefore important not to use the unit alone to specify the quantity. This applies not only to scientific and technical texts, but also, for example, to measuring instruments (i.e. an instrument read-out should indicate both the unit and the quantity measured).

A derived unit can often be expressed in different ways by combining base units with derived units having special names. Joule, for example, may formally be written newton metre, or kilogram metre squared per second squared. This, however, is an algebraic freedom to be governed by common sense physical considerations; in a given situation some forms may be more helpful than others.

In practice, with certain quantities, preference is given to the use of certain special unit names, or combinations of unit names, to facilitate the distinction between different quantities having the same dimension. When using this freedom, one may recall the process by which the quantity is defined. For example, the quantity torque may be thought of as the cross product of force and distance, suggesting the unit newton metre, or it may be thought of as energy per angle, suggesting the unit joule per radian. The SI unit of frequency is given as the hertz, implying the unit cycles per second; the SI unit of angular velocity is given as the radian per second; and the SI unit of activity is designated the becquerel, implying the unit counts per second. Although it would be formally correct to write all three of these units as the reciprocal second, the use of the different names emphasises the different nature of the quantities concerned. Using the unit radian per second for angular velocity, and hertz for frequency, also emphasizes that the numerical value of the angular velocity in radian per second is 2π times the numerical value of the corresponding frequency in hertz.

In the field of ionizing radiation, the SI unit of activity is designated the becquerel rather than the reciprocal second, and the SI units of absorbed dose and dose equivalent are designated the gray and the sievert, respectively, rather than the joule per kilogram. The special names becquerel, gray, and sievert were specifically introduced because of the dangers to human health that might arise from mistakes involving the units reciprocal second and joule per kilogram, in case the latter units were incorrectly taken to identify the different quantities involved.

We're all correct.

[SameSame]

[/quote="International Bureau of Weights and Measures"

Joule, for example, may formally be written newton metre, or kilogram metre squared per second squared.

… quantity torque may be thought of as the cross product of force and distance, suggesting the unit newton metre, or it may be thought of as energy per angle, suggesting the unit joule per radian.

We're all correct.

[/quote]

It's the application to which the unit is used that determines how it is written. But to say torque is not energy is incorrect. It is a form of energy and this particular form of energy is referred to as torque to avoid confusion with other forms of energy.

My point has been to get people to try and understand how torque is the mechanical form of energy, so that someone does not just quote some line that it's incorrect to refer to energy as torque and then come to the conclusion that they are not related at all. They are. (This entire discussion actually stemmed from people saying that 1J does not equal 1 Nm. ) This is truly my last word on the topic now.

[Shooty81]

[quote="International Bureau of Weights and Measures"

Joule, for example, may formally be written newton metre, or kilogram metre squared per second squared.

… quantity torque may be thought of as the cross product of force and distance, suggesting the unit newton metre, or it may be thought of as energy per angle, suggesting the unit joule per radian.

We're all correct.

It's the application to which the unit is used that determines how it is written. But to say torque is not energy is incorrect. It is a form of energy and this particular form of energy is referred to as torque to avoid confusion with other forms of energy.

My point has been to get people to try and understand how torque is the mechanical form of energy, so that someone does not just quote some line that it's incorrect to refer to energy as torque and then come to the conclusion that they are not related at all. They are. (This entire discussion actually stemmed from people saying that 1J does not equal 1 Nm. ) This is truly my last word on the topic now.

No. Not correct. Torque is no energy.

Lets's do some Basic physics:

I try to explain:
let's take a linear moving system:
I think we all agree on what a force is. For example a force of 1N pulling in a certain direction.
If the object to which the force is applied moves by 1m in the same direction, a energy of 1N*1m=1Nm is consumed. It is calculated by the force times the distance.

If we have the same constellation in a rotating system:
Lets imagine we have a torque of 1Nm. This is actually something like a "rotating force". It is applied to an object which can rotate. If it rotates by 1 rad (which is about 57.3 deg), then also 1Nm of energy is consumed.
Now there is one Thing to know: rad is not really a unit, it is actually "1". So in the Units it does not appear. That way, the torque (or "rotating force") has the same unit as the energy which is calculated by the torque times the angle, the angle in the rotating system corresponds to the distance in the linear moving system.

I hope this helps to understand.

Another way of thinking: a force is no energy, and only by applying a force to a lever, it does not get to energy. You will only need energy when it moves. In engineering it is very common to convert linear and rotating Systems into each others. Therefore the torque can be translated to a froce. While energy stays energy.

[Jersey Tom]

Everywhere I've looked has described torque as 'rotational force'.
If that is easily dismissed as "not energy" I'd like to know why.

...because force isn't energy? Just the same as an apple isn't an orange, and blue isn't red. Two totally different concepts.

Torque is a twisting force, yes. Like if you've got a stuck jar and are trying to twist the lid off.

I'll use an example using linear force and energy. Lets say your car runs out of gas, and you have to push it off the road. Two possible scenarios. In one, you forget to release the parking brake. So you get behind the car, push with all your might, and the car doesn't budge. Doesn't move an inch. You've used a lot of force... but nothing about the car has changed, right? It's just sitting there, there's been no actual transfer of energy.

So then second scenario, after you catch your breath you remember the brake, go in, take it off, and get behind the car again. You push like hell - and the car moves! Now it's slowly rolling. It has energy - energy of motion.

You might use the same force in both cases, but clearly the resulting kinetic energy of the car is different.

[SameSame]

Everywhere I've looked has described torque as 'rotational force'.
If that is easily dismissed as "not energy" I'd like to know why.

...because force isn't energy? Just the same as an apple isn't an orange, and blue isn't red. Two totally different concepts.

Torque is a twisting force, yes. Like if you've got a stuck jar and are trying to twist the lid off.

I'll use an example using linear force and energy. Lets say your car runs out of gas, and you have to push it off the road. Two possible scenarios. In one, you forget to release the parking brake. So you get behind the car, push with all your might, and the car doesn't budge. Doesn't move an inch. You've used a lot of force... but nothing about the car has changed, right? It's just sitting there, there's been no actual transfer of energy.

So then second scenario, after you catch your breath you remember the brake, go in, take it off, and get behind the car again. You push like hell - and the car moves! Now it's slowly rolling. It has energy - energy of motion.

You might use the same force in both cases, but clearly the resulting kinetic energy of the car is different.

Glad there is a thread to discuss this now!

That's exactly the point! Energy is only generated when a force acts over a distance. So in the first case there is no energy as you just stated, but in the second the force acted over a distance (Nm) and therefore there is energy.

Torque is NOT a force. This seems to be confusing people for some reason.

[Jolle]

Everywhere I've looked has described torque as 'rotational force'.
If that is easily dismissed as "not energy" I'd like to know why.

...because force isn't energy? Just the same as an apple isn't an orange, and blue isn't red. Two totally different concepts.

Torque is a twisting force, yes. Like if you've got a stuck jar and are trying to twist the lid off.

I'll use an example using linear force and energy. Lets say your car runs out of gas, and you have to push it off the road. Two possible scenarios. In one, you forget to release the parking brake. So you get behind the car, push with all your might, and the car doesn't budge. Doesn't move an inch. You've used a lot of force... but nothing about the car has changed, right? It's just sitting there, there's been no actual transfer of energy.

So then second scenario, after you catch your breath you remember the brake, go in, take it off, and get behind the car again. You push like hell - and the car moves! Now it's slowly rolling. It has energy - energy of motion.

You might use the same force in both cases, but clearly the resulting kinetic energy of the car is different.

Glad there is a thread to discuss this now!

That's exactly the point! Energy is only generated when a force acts over a distance. So in the first case there is no energy as you just stated, but in the second the force acted over a distance (Nm) and therefore there is energy.

Torque is NOT a force. This seems to be confusing people for some reason.

Simple:

Torque is force at a meter.
Energy is force over a meter.
Power is force over a meter in a second.

[Jersey Tom]

Torque is NOT a force. This seems to be confusing people for some reason.

Torque is not force, but I'd make the case that it's the rotational equivalent of force. It's at least conceptually related. Force * linear displacement = work. Torque * rotational displacement = work.

[Jolle]

https://postimg.org/image/g7wig8mgl/

[SameSame]

Just realized I was explaining myself extremely poorly. My point was that when the NET torque acting on a body was not zero, then the body had energy ( which is another way of saying the torque acts through an angle). I realize now how I phrased a lot of my stuff could be extremely confusing.

[mcdenife]

Torque is NOT a force. This seems to be confusing people for some reason.

Torque is not force, but I'd make the case that it's the rotational equivalent of force. It's at least conceptually related. Force * linear displacement = work. Torque * rotational displacement = work.

JT, afraid I have to disagree. Torque is a force, a rotational or twisting force as you mentioned previously

[SameSame]

https://postimg.org/image/g7wig8mgl/
https://postimg.org/image/g7wig8mgl/

The perfect explanation

[Jolle]

https://postimg.org/image/g7wig8mgl/
https://postimg.org/image/g7wig8mgl/

The perfect explanation

Dutch high school physics pay off in later life eventually. But this also shows that torque does not equal energy. Torque is by definition stationary, it's in rest. It can have energy stored (like a spring), but that is something completely different.