Torque vs Energy. Same units, not the same thing

[gruntguru]

I have been trying very hard not to jump into this thread - there is so much BS flying its hard to know where to start. A quick summary of some facts (I know most of them have appeared in earlier posts but I thought I might put them together in one place). The main outcome (looking at points 3 and 4 below) is that torque and work are totally different quantities. They are only remotely related to one another and then only by introducing a third property (rotation).

1. A "scalar" is a physical quantity that has magnitude but no direction.

2. A "vector" is a physical quantity that has magnitude and direction.

3. Torque = force x lever arm (perpendicular displacement from axis to force). Note this is a "cross" product of two vectors so torque is also a vector, pointing along an axis perpendicular to both the force and the lever arm. Note also that only the component of the lever arm which is perpendicular to the force contributes to the cross product. (eg if you push along a spanner you do not generate any torque)

4. Linear work (energy) = force . displacement parallel to the force. This a "dot" product of two vectors so work is a scalar (it has no direction).

5. Rotational work (energy) = torque . rotational displacement parallel to the torque. Once again the two vectors are multiplied using a dot product, so the work is again a scalar. No rotation -> no work.

6. Power is the rate at which energy is released or transferred. Since rotational energy is torque . displacement, rotational power is "rotational energy rate" which is torque . rotational displacement rate (also know as angular velocity). Whether this is expressed as radians per second or rpm doesn't really matter - that is just a "units" issue which is easily fixed with conversion factors.

[jz11]

http://www.f1technical.net/forum/viewto ... 57#p651157

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.

Anybody want to own up for -1 this post? I can't see anything technically wrong with it and assume you just disagree.

Power = Torque x Rpm

Looking at a single revolution, Torque = Power/1 which matches my simple explanation above.

Once you look at a time period say 1 minute then Power = Torque x nr of revolutions per minute - matches my 2nd statement.

If you take Torque as fixed then the only way to increase power is to increase nr of revolutions per minute - matches my final statement.

others explained it with reasoning, I will add the rational to it

power = torque * rpm >
power = torque * 1 >
power / 1 = torque >
power = torque

this is a prime example of when math is used in a wrong way - to explain what you want, not what the language was used to describe in the first place, because that is what variables in formulas are, they describe relationships between things, and those things and the whole expression is what matters, if you keep this in mind, you will never ever make this assumption that power = torque, because language says so - this logic is 100% backwards thinking

torque - is a potential to do something (without getting into technicalities)
energy - how much it took to do this something
power - how fast you want this something to be done

[pgfpro]

Very well said!!!

I have been trying very hard not to jump into this thread - there is so much BS flying its hard to know where to start. A quick summary of some facts (I know most of them have appeared in earlier posts but I thought I might put them together in one place). The main outcome (looking at points 3 and 4 below) is that torque and work are totally different quantities. They are only remotely related to one another and then only by introducing a third property (rotation).

1. A "scalar" is a physical quantity that has magnitude but no direction.

2. A "vector" is a physical quantity that has magnitude and direction.

3. Torque = force x lever arm (perpendicular displacement from axis to force). Note this is a "cross" product of two vectors so torque is also a vector, pointing along an axis perpendicular to both the force and the lever arm. Note also that only the component of the lever arm which is perpendicular to the force contributes to the cross product. (eg if you push along a spanner you do not generate any torque)

4. Linear work (energy) = force . displacement parallel to the force. This a "dot" product of two vectors so work is a scalar (it has no direction).

5. Rotational work (energy) = torque . rotational displacement parallel to the torque. Once again the two vectors are multiplied using a dot product, so the work is again a scalar. No rotation -> no work.

6. Power is the rate at which energy is released or transferred. Since rotational energy is torque . displacement, rotational power is "rotational energy rate" which is torque . rotational displacement rate (also know as angular velocity). Whether this is expressed as radians per second or rpm doesn't really matter - that is just a "units" issue which is easily fixed with conversion factors.

[PlatinumZealot]

They dont call him guru for nuffin.
Said it better than i could. That pretty much sums it up.

[mrluke]

Apologies, at no point was I trying to say that torque and power were the same thing :/

I was trying to draw the distinction between power having a time element whereas torque doesn't.

Clearly I expressed that badly.

[strad]

Heavens
Do we really need to thrash this to death again?

[Edis]

Again, this long winded discussion is why it's just easier to measure torque at some other reference point, like directly at the end of the crank/flywheel or the wheels. Because the conversion of chemical to mechanical energy is a very inefficient process with thousands of confounding variables. It's easier to just assume an average of all the combustion events, masses and inertia as one output, and call it torque. It's a simplification which ignores a sea of interdependent variables such as friction, leverage, balance forces, harmonics, vibration, temperature, temperature gradients, imperfections in the machined surfaces.

Measuring the power acting on the piston isn't a problem if you want to do that instead, all you need is a pressure indicator. This is refered to as indicated power while the power output on the crankshaft measured with a dyno is refered to as brake power (hence ihp and bhp, when using horsepower). The difference between indicated power and brake power is the friction loss, and this loss is typically between 10 and 25%.

[FoxHound]

Then would it be incorrect to say that Horsepower is the rate at which Torque is delivered?
Sorry to bang on, but I'm trying to simplify this to explain it accurately, with as much brevity as possible, without being incorrect.

Horsepower can be defined as how fast the engine can deliver torque to a load. Correct?
And torque is the measure of how much twisting force an engine can produce. Correct?

One is related to the other, but both are influenced either by time(HP), or by distance(torque)?

[Pierce89]

Heavens
Do we really need to thrash this to death again?

Well,obviously we do. We always get poorly educated new members every season, some of whom will think it's the the world who is wrong not himself.(I'm obviously not talking about you JET, your argument is more about conversational practicalities than physics).The guy claiming torque is energy is surely a fan of rollelderly rather than f1 and just got lost in the wrong forum.

[rjsa]

Then would it be incorrect to say that Horsepower is the rate at which Torque is delivered?
Sorry to bang on, but I'm trying to simplify this to explain it accurately, with as much brevity as possible, without being incorrect.

Horsepower can be defined as how fast the engine can deliver torque to a load. Correct?
And torque is the measure of how much twisting force an engine can produce. Correct?

One is related to the other, but both are influenced either by time(HP), or by distance(torque)?

No. Power is the rate at which energy is delivered, not force. And torque is force times distance from rotation center, not energy. It's the root of this silly argument.

[strad]

But you always wind up making it far too complicated.
On a certain level it is as complex as you make it.
However to the average guy or especially a younger person whom you're talking way over their heads it's as simple as the old adage: Torque gets the car moving and horsepower makes it go fast.
I know , I know, That is an over simplification but you guys go in for over complication.
Now you can return to picking fly droppings out of the pepper.

[FoxHound]

Then would it be incorrect to say that Horsepower is the rate at which Torque is delivered?
Sorry to bang on, but I'm trying to simplify this to explain it accurately, with as much brevity as possible, without being incorrect.

Horsepower can be defined as how fast the engine can deliver torque to a load. Correct?
And torque is the measure of how much twisting force an engine can produce. Correct?

One is related to the other, but both are influenced either by time(HP), or by distance(torque)?

No. Power is the rate at which energy is delivered, not force. And torque is force times distance from rotation center, not energy. It's the root of this silly argument.

Ok so in one sentence, can you give me a definition of the differentiation of Torque to Horsepower that is accurate?
Because there is a ton of misinformation on this on the internetz.
And we can also finally put this to bed(arguably, perhaps).

[strad]

hahahahahahahaha
never
They will pick apart anything posted.
It's their form of recreation.

[SameSame]

Then would it be incorrect to say that Horsepower is the rate at which Torque is delivered?
Sorry to bang on, but I'm trying to simplify this to explain it accurately, with as much brevity as possible, without being incorrect.

Horsepower can be defined as how fast the engine can deliver torque to a load. Correct?
And torque is the measure of how much twisting force an engine can produce. Correct?

One is related to the other, but both are influenced either by time(HP), or by distance(torque)?

No. Power is the rate at which energy is delivered, not force. And torque is force times distance from rotation center, not energy. It's the root of this silly argument.

Ok so in one sentence, can you give me a definition of the differentiation of Torque to Horsepower that is accurate?
Because there is a ton of misinformation on this on the internetz.
And we can also finally put this to bed(arguably, perhaps).

Say you have a shaft that experiences a net torque and that shaft rotates 1 revolution. The speed at which the torque acts through that revolution is power/horsepower. So the less time it takes that torque to "turn" one revolution the higher the power (because the shaft speed is therefore higher). i.e. 100 N.m acts through 2 radians per second (1 revolution per second) will result in 100*2*pi = 0.628 kW of power

Edit: FoxHound Torque is a measure of how much "twisting force" the engine can deliver, but Horsepower is defined as how fast the engine can deliver torque through an angle to a load.

[Brian Coat]

I now understand why doctors roll their eyes when patients say they "Googled" their symptoms on the internet.