Ft-Lb vs. Lb-Ft

D

deadbugdug

Registered
(Hope I got the right forum)

The short story long:

I went to my Ford Maintenance CD-ROM to check a torque value for my beloved Mark VIII, and noticed that all the values were given in "Lb-Ft". That's nice, except my trusty torque wrench gives the settings as "Ft-Lb".

"So what's the difference?" I asked myself. A search of the internet (suprisingly) did not readily answer the question. I did happen upon a car forum site where an interesting flame war was waging, but no real clear answer other than some dude I don't know stating "they are one in the same."

Once again, I defer to the trusted experts of this wonderful forum... So quite simply, are the terms interchangeable? That is all I really need to know, because I've read enough about torque, work, Nm, quotients, and a bunch of physics explanations and equasions that are nice, but does not simply answer my question!!!

Thanks.......!
 
RE: Ft-Lb vs. Lb-Ft

They are the same and completely interchangeable.

The amount of torque applied to a bolt is a product of the amount of force applied to the wrench (lever) and the length of the lever (wrench). This would be expressed as a unit of length (ie: foot, meter) multiplied by a unit of force (ie: newton, lb). Because multiplication is commutative (ie: x*y = y*x) it doesn't matter in which order the values are multiplied. And it doesn't really matter in which order the units are presented. You may see ft-lb and lb-ft both used, but when using the metric system it will almost always be "newton-meter", i've never heard someone speak of a "meter-newton." The "-" used when people usually express the units is not a mathematical symbol but a grammatical one.

So, ft-lb and lb-ft are one and the same.
 
RE: Ft-Lb vs. Lb-Ft

Thank you thank you THANK YOU!

That was simple and concise. Now, for entertainment purposes only, if you all desire, this was the link I ended up on with my search:

www.car-forums.com/s9/t10462.html

Apparently, somebody got their Wheaties pee'd in, and decided to cry about it. Oh, and to split hairs on things like Ft-Lb vs. Ft/Lb vs. Ft.Lb . I want to express my gratitude and relief that I haven't seen too much of that flaming nonsense in this site. And I hope I don't pay for that last comment!

Anywhoo, thanks again, sleeper, for your response.
 
RE: Ft-Lb vs. Lb-Ft

No problem, Doug.


[div class="dcquote"][strong]Quote[/strong]
www.car-forums.com/s9/t10462.html
[/div]

OMG what flaming idiots. ::nono::

To clear up any discussion on the ft/lb, ft.lb, etc., again, the / and . in those "units" are grammatical symbols and not mathematical ones. If you wanted to use a mathematical symbol, you'd use ft*lb or lb*ft.
 
RE: Ft-Lb vs. Lb-Ft

[div class="dcquote"][strong]Quote[/strong]
They are the same and completely interchangeable.The amount of torque applied to a bolt is a product of the amount of force applied to the wrench (lever) and the length of the lever (wrench). This would be expressed as a unit of length (ie: foot, meter) multiplied by a unit of force (ie: newton, lb). Because multiplication is commutative (ie: x*y = y*x) it doesn't matter in which order the values are multiplied. And it doesn't really matter in which order the units are presented. You may see ft-lb and lb-ft both used, but when using the metric system it will almost always be "newton-meter", i've never heard someone speak of a "meter-newton." The "-" used when people usually express the units is not a mathematical symbol but a grammatical one.So, ft-lb and lb-ft are one and the same.
[/div]

3ft x 5lbs = 15ft*lbs

5lbs x 3ft = 15lbs*ft
 
RE: Ft-Lb vs. Lb-Ft

[div class="dcquote"][strong]Quote[/strong]
3ft x 5lbs = 15ft*lbs5lbs x 3ft = 15lbs*ft
[/div]

3ft x 5lbs = 15ft*lbs = 5lbs x 3ft = 15lbs*ft = 1 lb * 15 ft = 15 ft * 1 lb = 20.34 Nm

All the same

and if you want to get picky, you should specify pound-force as opposed to pound-mass.
 
RE: Ft-Lb vs. Lb-Ft

[div class="dcquote"][strong]Quote[/strong]
[div class="dcquote"][strong]Quote[/strong]3ft x 5lbs = 15ft*lbs5lbs x 3ft = 15lbs*ft[/div]3ft x 5lbs = 15ft*lbs = 5lbs x 3ft = 15lbs*ft = 1 lb * 15 ft = 15 ft * 1 lb = 20.34 NmAll the sameand if you want to get picky, you should specify pound-force as opposed to pound-mass.
[/div]

Right...I meant to imply that I agree with you.

My bad.
 
RE: Ft-Lb vs. Lb-Ft

I wasn't quite sure if you were agreeing or not, so i just clarified a little.

The whole lb-mass vs. lb-force thing can be a PITA... which is why it's often much easier to do those calculations in metric.
 
RE: Ft-Lb vs. Lb-Ft

I once had to torque a small nut to 6 in-lb on the end of a turbine shaft. We didn't have a torque driver for that range, so I tied a 1 lb weight to a 6 inch wrench and rotated the turbine until the wrench was level with the ground (string was attached 6 inches from the shaft centerline).

One pound on a foot long lever equals one foot-pound (or pound-foot if you prefer).

Note: A 200 lb man, with his weight at the end of a 4 foot long cheater bar, exerts 800 lb-ft of torque without bouncing...And you wondered how that ratchet broke.
 
RE: Ft-Lb vs. Lb-Ft

[div class="dcquote"][strong]Quote[/strong]
Note: A 200 lb man, with his weight at the end of a 4 foot long cheater bar, exerts 800 lb-ft of torque without bouncing...
[/div]

I've done that! :7
 
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