Seen it typed Lbs-Ft and Ft-Lbs.

Heard it said 'pounds per foot' and 'Foot-Pounds'.

Yes, it is a noobie question, but I was just sittin' here makin up an Engine Code Chart (how I keep myself from getting bored to death), and it seems like every site switches back and forth between the two.

Is there a correct way to write/type it, or are they both correct and it's just a matter of opinion, Like tomatoe/tom-a-ta.

 

My questions just keep popping up:

1.) At http://www.teirney.net/civic/b16AReference.htm, the guy uses KgM as the unit or torque. Is this Kilograms per meter?

2.) At http://www.civic4g.com/specs.htm, the guy uses NM as the unit for torque. What is this? I couldn't come up with anything, except for Newton-Meters, which actually, now that I think about it, is probably it, because Newton is a measurement of force, right?

 

It's force x length. Unfortunately, that's also the units for energy. Convention is to use foot-pounds for energy, & pound-foot for torque.

NOTICE that it it not pounds PER foot. Pounds per foot would be lb/ft. That would be the units for a spring constant.

kg-m or newton-meter also, but remember it's not kg PER meter.

As long as we're getting technical here, it's force, not mass. So lbf-ft would be more correct than lbm-ft. Also N-m is more correct than kg-m. I guess kgf-m would be ok but I don't see that used much.

 

So it's either lb/ft or ft/lbs depending on what you are measuring? Think we could get anymore confusing?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Chiovnidca &raquo;</TD></TR><TR><TD CLASS="quote">So it's either lb/ft or ft/lbs depending on what you are measuring? Think we could get anymore confusing? </TD></TR></TABLE>

To tell you the truth, I am even more confused than I was before I asked the question...

What are you saying now?

 

He meant ft-lb or lb-ft. Like JimBlake said, the convention is to use ft-lb for energy and lb-ft for torque. Just use lb-ft and don't worry about it

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Chiovnidca &raquo;</TD></TR><TR><TD CLASS="quote">So it's either lb/ft or ft/lbs depending on what you are measuring? Think we could get anymore confusing? </TD></TR></TABLE>No, don't use "/" because that would be force divided by length. A spring constant could be expressed in lb/ft. Torque is force times length.

I probably shouldn't have used a minus sign up there, since I didn't want to imply subtraction.

It's too bad that energy & torque both work out to the same units, but that's just tough. For many years it's been the accepted practice to use lb*ft for torque & ft*lb for energy. But old habits die hard, & there's lots of torque wrenches still marked in ft*lb units.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JimBlake &raquo;</TD></TR><TR><TD CLASS="quote">No, don't use "/" because that would be force divided by length.

</TD></TR></TABLE>
Good point, dont know when I started doing that.


<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JimBlake &raquo;</TD></TR><TR><TD CLASS="quote">
I probably shouldn't have used a minus sign up there, since I didn't want to imply subtraction.

</TD></TR></TABLE>
Helms manuals use the minus sign. The newer ones also list bolt torque as "lbf-ft".
What's the extra "f" for???

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Chiovnidca &raquo;</TD></TR><TR><TD CLASS="quote">Helms manuals use the minus sign. The newer ones also list bolt torque as "lbf-ft".
What's the extra "f" for???</TD></TR></TABLE>Yeah, everybody uses the minus sign, until you key the units into some software like MathCad.

Technically, force & mass aren't interchangeable. But nobody uses the units of slugs or poundals, so they use lbf for 'pounds of force' & lbm for 'pounds of mass'. Doing engineering calculations it's real important not to get the 2 confused, because they're numerically different by a factor of 32 ft/sec^2. So I never use just 'lb'. (The f or m are usually subscripts.)

So if you pick up a pound of rocks, you're talking about 1 lbm. At sea level it's weight would be a force of 1 lbf. On the moon it's weight would be a force of 1/6 lbf. But even on the moon it would have the momentum (if it were moving) based on 1 lbm.

SI is cleaner, because Newtons are force & kilograms are mass. But just to make it more confusing, there's also kgf for 'kilograms of force'... So a torque wrench should never say kg*m, it should say 'kgf*m'.

Are we confuscipated yet?

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Justin_Bradley &raquo;</TD></TR><TR><TD CLASS="quote">Yes, it is a noobie question...</TD></TR></TABLE>Is it really???

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JimBlake &raquo;</TD></TR><TR><TD CLASS="quote"> so they use lbf for 'pounds of force' & lbm for 'pounds of mass'. </TD></TR></TABLE>
Questions getting answered.