Some say the former, some the latter. What's correct?

 

Nm
lb-ft

Force x distance m8.

 

That's what I thought. Just spotted a few ft-lb abbreviations banded about and thought I'd asked.

 

lb/ft

 

Yep ... i'm guilty of this but it should be lb per ft.

 

It is NOT lb per fit. It's not a ratio it's a product you pull with so many lb's force over a leverage of so many feet.

So pulling with 10 lb force on a 1 foot lever is 10 ftlb and applies the same torque as pulling with 1 lb force on a 10 foot lever.

As it's a product lbft and ftlb are both the same in the same way as 5 times 3 equals 15 and 3 times 5 also equals 15.

 

Totally agree Chelspeed!

lb/ft is a measure of tension.

lb ft, ft lb, lb.ft, ft.lb, lbft, ftlb, lb-ft, ft-lb are all legitimate imperial notations for torque as far as I'm concerned.

 

Nice one, that's cleared that up then.

 

So it should, it is barely secondary school physics!

 

So what do you call a bloke with a bird on his head?
LOL.

 

I don't understand all this technical stuff. But the blokes called Cliff.

 

The reason it comes out at lb ft is your measuring weight 1 foot off the engine, so imperial would be lb ft, metric would be KG NM.

Tony

 

spot on mate.

Anyway lbft is old people talk. Its Nm these days folks - this is the metric age

 

Which is why so many car adverts and RRoads state....210 bhp and 340Nm!
This country went metric in 70 or 72 but it is hard to see it at times.
Graham

 

lol it is infact year 9 physics, so not even GCSE ( speaking as a science teacher at secondary school lol)

should be easy to grasp lol.

Moment, Torque, whatever you want to call it, it is Force x Distance and either lb/ft or Nm depending on how old you are lol

 

If it is so easy to grasp why do you put a division "/" in between the unit of force and the unit of distance when it is a multiplier which would be implied by nothing, a dot, an x, a * or anything other than / ?

 

If you need to put a seperator in, use a period (dot or full stop) to be correct, putting in a slash is just a coloquialism(sp?) really.

A moment is a product of force and offset (distance from the pivot). A product (two things multiplied together) is the same wich ever way round you do it. So feet-pounds is the same as pounds-feet, although I am sure you will find people that say otherwise.

The easy way to work with secondary (and above) units, is to keep the units present during any calculation or formulae, and the input units of measure are handled like regular algebra to work out the output units.

Paul

 

I agree with Paul.
Graham.

 

Good question!

You should ask a science teacher!



























Oh, you did!

 

 

Kids naturally grasp measurements such as Foot, Inch, Mile, Pound. I don't know why, but they do. I'm sure that's why they persist.

 

No, metric would be NM.

In Earth's gravity at sea level, a kilogramme exerts a force of 9.81 Newtons. Elsewhere (when you're driving on Mars for example ) a kg would exhibit a different force. From Newton's first law of motion, Force (Newtons) = Mass (kg) * Acceleration (due to gravity = 9.81 metres/second squared)

lbft (or ftlb) is technically a little dodgy as lb should mean "lb force" which is the force exhibited by 1 lb mass in Earth's gravity.

Is that still GCSE? I forget which bits of physics I did where!

 

the pound is not a unit of mass, but of force. There is no imperial fundamental unit of mass.

 

/pedant mode - on

> No, metric would be NM.

Actually it's Nm.

/off

 

Secondary school some time ago!! I'm a child of the 60's (just ) and I have only ever been taught metric units.

[hobbyhorse=on]
The sooner we move completely to SI units for everything (except pints of beer) the better. Roll on speed limits in km/h!
[hobbyhorse=off]

 

Just as a warning, if we move everything to metric we end up with definitions for measurements like the following:

a "second" =

• The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.This definition refers to a caesium atom at rest at a temperature of 0 K.

Rich

 

...whereas with imperial units we have :-

Length:-
12 inches to a foot
3 feet to a yard
1760 yards to a mile
8 furlongs to a mile (furlong = 220 yards)
10 chains to a furlong (chain = 22 yards)

Volumes and masses are equally unfathomable (and don't forget ambiguity inherent with the lb being used incorrectly for both weight & mass).

Seen any temerature measure in degrees Rankine recently?

I'll keep SI units thank you very much

 

Taken from Engineer magazine today:

Letter from a Briam Hammond about metric/imperial

....does anyone really want to go back to Links (7.92'') and Poles(66 ft, or 18ft in Woodland Measure, 24ft in Cheshire or 24.7065yds in Scotland)?

Does anyone even remember what a Slug is?(it's the mass in which a force of 1 lb produces an accelleration of 1 ft/sec/sec).....

and one gallon = 6.22883 cu ft.

Metric for me.
I am a child of the 60's (and 50's) and I was taught both systems, so can converse fluently with old and young people!

Graham.

 

I thought it was pounds-feet as I have to stand on an extension bar with my "feet" to get the hub nuts on my Caterham done up properly (well as close to properly as I can get and I haven't had one fall off yet!).

And in real mega-pedant mode I think the plural of Newton (the force, not the person) is Newton.

And no wonder my kids learn nuffink at school if their teachers put "lol" 4 times in one post :-)))

Graham

 

Not the greatest advert for Scoobysport's technical excellence