Torque vs Energy. Same units, not the same thing

[SameSame]

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

Googling one's symptoms will always result in a conclusion that near death is imminent

[Dazed1]

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.

Well said indeed! We should all get a degree now. =D>

[rjsa]

This is high school physics. I give up. Just hope I never touch a piece of machinery engineered by someone who couldn't figure this out by the time they were 16.

[Cold Fussion]

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).

Just read this post. If you cannot understand it after reading this then you'll need to pick up a physics textbook if you want to try and understand it.

[FoxHound]

Just read this post.[/url] If you cannot understand it after reading this then you'll need to pick up a physics textbook if you want to try and understand it.

I've read this post. I've upvoted this post.

I'm was attempting to condense this post into a sentence, so that it would be explicable to most. Rjsa helped out.
THE END.

[Cold Fussion]

Just read this post.[/url] If you cannot understand it after reading this then you'll need to pick up a physics textbook if you want to try and understand it.

I've read this post. I've upvoted this post.

I'm was attempting to condense this post into a sentence, so that it would be explicable to most. Rjsa helped out.
THE END.

Condensing into one sentence is just arbitrary 'simplification'. The explanation Grunt Guru provides is about as simple as you can realistically make it.

[Tommy Cookers]

since people are requesting simplicity rather than mention of scalar and vector quantities etc ....

the OP having proposed that a diesel engine with higher torque but lower power than a petrol engine would be quicker on track
is wrong

the car's performance is proportionate to the axle torque not to the crankshaft torque
the axle torque is the crankshaft torque multiplied by the gearing downstream of the crankshaft
so the petrol engined car would have greater axle torque than the diesel engined car would (when both are optimally geared for the task)
because its greater power will give it greater axle torque

so there is no such thing as the mythical 'torque acceleration' (as aired in the modern world by D Coulthard)
(unless you wrongly regard torque as meaning a bottom-heavy power/rpm curve)

yes, a tractor with 1m radius wheels will in steadily travelling 1m in 1 sec develop an axle torque numerically equal to the power (if I guess correctly)
so what !


with apologies if the above has already been said by some other poster, I shall resume turning in my grave

[godlameroso]

When I tune cars for customers, I don't even bother looking at raw numbers or the horse power, I tune for torque across the whole power band. In the really real world, a 7hp peak difference is meaningless when you can gain 15-20 ft lbs of torque across 80% of the useful rpm range. At least with the jalopies I tune.

[hollus]

How much extra power do those extra 15-20 ft lbs of torque represent?

[sosic2121]

How much extra power do those extra 15-20 ft lbs of torque represent?

that's the funny bit.
it depends on rpm.

[hollus]

I know. So how much extra power comes together with the extra torque... at those rpm where torque is being increased?

[sosic2121]

I know. So how much extra power comes together with the extra torque... at those rpm where torque is being increased?

IF my calculations are correct,
10 Nm is equal to 1.42 HP per 1000rpm.
10 lbft is 1.93 HP per 1000rpm.

[godlameroso]

Between 4,500 to ~7,900 there's an across the board improvement 15-20ft lbs of tq, but there's a 7hp deficit at 8,400 rpm. Compared to the same car with another "tune" and different mods, granted we're talking about 167 ft lbs vs 148 ft lbs peak difference, and on average about 15 ft lbs over 3,000 rpm. I don't know what that equates to power wise probably 10 hp average increase everywhere in that range but a little bit less peak.

[sosic2121]

Between 4,500 to ~7,900 there's an across the board improvement 15-20ft lbs of tq, but there's a 7hp deficit at 8,400 rpm. Compared to the same car with another "tune" and different mods, granted we're talking about 167 ft lbs vs 148 ft lbs peak difference, and on average about 15 ft lbs over 3,000 rpm. I don't know what that equates to power wise probably 10 hp average increase everywhere in that range but a little bit less peak.

Sounds like really big midrange gain and small top end loss.

When you shift up revs are going to drop from 8500 to around 6500rpm.
At those revs(6.5k) power difference will be up to 20hp.
So, I think your "weaker" engine will be faster, especially in lower gears.

[hollus]

What I dont understand then is the choice of language. You say that you sacrifice peak power for a low end torque gain. No wonder people get tricked!
You are saying that you are sacrificing 7hp at the peak rpm which is rarely used to gain 10hp at rev ranges that are used more often. Of course it is an improvement, you are increasing the power most of the time.
Why talk of power / torque? Why not choose a torque/torque or power/power wording?
It is like saying that Bolt made his frist 50 meters at 36 km/h but then changed to 10m/s for the final spurt.