musings about torque

peasant · 26-01-2008 2:39pm #1

Had to tighten a particular nut on the car today and the book says ..tighten with 350 Nm.

Now ...I don't have a torque wrench, but I happen to be a hefty fellow, weighing in at close to a hundred kilos. 1 Kilo is ~ 10N (9.8something) ...so 100 kg is ~1000 N. So if I stood on a meter long lever, I could produce a force of 1000Nm. As it happens, the handle for my wrench is exactly 35 cm ...so stand on that and hey presto ...350 Nm, problem solved, nut tightened correctly.

That brought me to think ...350 Nm (or Torques, as Clarkson calls it) is a pretty decent figure for a car engine, verging into sports car territory (or TD territory) ...1000 Nm is a (very) high perfomance car (the Bugatti Veyron produces 1250 Nm) ...yet the thought of me bouncing up and down on a meter long lever conjures up all sorts of images and comparisons ...but "high performance" sure isn't one of them

On the other hand, my wheezy old diesel produces a miserly 140 Nm (or me on a 14 cm long lever

) yet it pulls its 1700 kg self and a two ton trailer up a hill without problems.

The mind boggles ...

Esel · 26-01-2008 2:50pm

Torque to yourself a lot?

Andrewf20 · 26-01-2008 4:29pm

Dont forget the gearing, combined with thousands of rpm.

JHMEG · 26-01-2008 5:38pm

The most impressive thing peasant is your use of brain power!

E92 · 27-01-2008 1:09am

1 kg = 9.77-9.83 N on Earth, depending on where you are(about 9.81 N in Ireland/UK). 1 kg ~ 1.63 N on the Moon for example.

Which proves that there is a huge difference between proper weight and what we incorrectly call "weight" in everyday speech:D!

What's 350 N m in what Clarkson calls "torques" i.e. pounds feet?

JHMEG · 27-01-2008 1:11am

E92 wrote: »

pounds feet?

They're called foot pounds. Don't ask me why...

E92 · 27-01-2008 1:16am

Andrewf20 wrote: »

Dont forget the gearing, combined with thousands of rpm.

Ah the good old torque multiplier! What's the formula for that again, and more to the point how can you use rpm for it, the SI unit for things like rpm is s^-1 i.e. Hertz(Hz) so you need rps instead of rpm for a start, and are gear ratios just a number you multiply the Hz by?

peasant · 27-01-2008 1:16am

wikipedia says:

1 foot-pound is equivalent to:

1.3558179483314004 newton meter (exactly)

E92 · 27-01-2008 1:25am

JHMEG wrote: »

They're called foot pounds. Don't ask me why...

I've heard Americans call them foot pounds on youtube, then again they write it as ft-lbs. I thought we called them pounds feet though(it certainly is written as lb ft), but it doesn't make a difference really as they have the exact same scientific meaning, and besides that most people don't know what torque is and only ever talk about power. Almost always I call lb ft "torques" if I'm ever talking about it to someone though:D!

Spit62500 · 27-01-2008 1:00pm

Apparently, foot pounds and pounds feet are two completely different things...

Torque is force times distance whereas work (the expenditure of energy) is distance times force.

'Torques' is a very dodgy term if you're looking to be accurate but probably easier to use in casual conversation if you're looking for immediate understanding from someone.

http://findarticles.com/p/articles/mi_qa3726/is_200409/ai_n9458018

E92 · 27-01-2008 1:56pm

Spit62500 wrote: »

Apparently, foot pounds and pounds feet are two completely different things...

Torque is force times distance whereas work (the expenditure of energy) is distance times force.

'Torques' is a very dodgy term if you're looking to be accurate but probably easier to use in casual conversation if you're looking for immediate understanding from someone.

Torque is force by displacement, distance is something else. Basically displacement is the shortest distance between 2 points.

Energy is the ability to do work. It is measured in Joules, which is force by displacement actually. i.e. the same unit as torque. Power is defined as work done per unit time. It is measured in Watts under the SI system which is Joules per second or Newton metres per second, so power in kW is the amount of torque in (Newton metres per second X 10³) N m s^-1 X10³ the engine can produce.

As for the relationship between power in bhp and torque in lb ft, I have absolutely no idea, which shows how useful the SI system is really!

Multiplication is commutative, so foot pounds are the same as pounds feet, if lb ft were not equal to ft lbs then what that would be saying is that 5 X 12 is not equal to 12 X 5 and of course we know that is not true. (For the benefit of Mathematicians and Physicists I'm well aware that this isn't always true e.g. Matrices, but in everyday Maths it most certainly is and that's all that matters here).

MrPudding · 27-01-2008 6:06pm

E92 wrote: »

Which proves that there is a huge difference between proper weight and what we incorrectly call "weight" in everyday speech:D!

You mean mass and weight?

E92 wrote: »

As for the relationship between power in bhp and torque in lb ft, I have absolutely no idea, which shows how useful the SI system is really!

It does seem confusing. I have two motorbikes, both are 100BHP but one of them has twice the torque of the other....

MrP

b318isp · 22-02-2008 2:59pm

E92 wrote: »

so power in kW is the amount of torque in (Newton metres per second X 10³) N m s^-1 X10³ the engine can produce.

Not quite, think of it as the torque (N m) being applied per revolution or per second (s^-1).

E92 wrote: »

As for the relationship between power in bhp and torque in lb ft, I have absolutely no idea, which shows how useful the SI system is really!

It's 5252. BHP=TORQUExRPM / 5252, all imperial of course.

--amadeus-- · 22-02-2008 3:33pm

How then does the relationship between rpm and increasing torque work.

Obviously the greater the rpms the greater the number of combustions cycles and the greater the energy transfered to the crankshaft and the faster it spins. Is the torque figure simply a measure of teh amount of energy so produced and output, expressed as Nm?

Wossack · 22-02-2008 4:18pm

b318isp wrote: »

Not quite, think of it as the torque (N m) being applied per revolution or per second (s^-1).

It's 5252. BHP=TORQUExRPM / 5252, all imperial of course.

reminds me of an interesting bit of trivia: on a dyno printout, the plots for torque and hp always cross at 5252 rpm

(sorry if thats what you just said, no speaky formulas, the number reminded me)

conneem-TT · 22-02-2008 5:17pm

I always found this a good read on torque, wheter it's acurate or not, maybe someone will comment

http://vettenet.org/torquehp.html

Andrewf20 · 22-02-2008 11:20pm

E92 wrote: »

Ah the good old torque multiplier! What's the formula for that again, and more to the point how can you use rpm for it, the SI unit for things like rpm is s^-1 i.e. Hertz(Hz) so you need rps instead of rpm for a start, and are gear ratios just a number you multiply the Hz by?

I was just jumping into the realm of power as well as torque, hence mentioning the rpm, to reflect his comments about the engine pulling his car + trailer up hills. That is all.

b318isp · 26-02-2008 11:57am

--amadeus-- wrote: »

How then does the relationship between rpm and increasing torque work.

Obviously the greater the rpms the greater the number of combustions cycles and the greater the energy transfered to the crankshaft and the faster it spins. Is the torque figure simply a measure of teh amount of energy so produced and output, expressed as Nm?

No, power is the measure.

musings about torque

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