topic Re: Swap between lbf and lbm in Mathcad

Swap between lbf and lbm

jdesai-2 — Thu, 03 May 2018 13:20:02 GMT

Hello,

If something weighs 10 pounds, I put M=10*lbm

The inertial load factor is LF=100gs (100 gees)

The force will be M*LF= 10*100=1000lbf

Why does MC screw up the units? I remember, if I used M*LF*g then it used to revert to lbf. It does not do so today.

What is the best way to do this

Re: Swap between lbf and lbm

MJG — Wed, 10 Jan 2018 18:13:20 GMT

Please clarify your problem. Uploading your file and/or screenshots would be helpful.

Here is what I get:

Re: Swap between lbf and lbm

Fred_Kohlhepp — Wed, 10 Jan 2018 18:13:34 GMT

Not sure what your problem is. In Prime 3.0:

Re: Swap between lbf and lbm

jdesai-2 — Wed, 10 Jan 2018 18:33:14 GMT

Never mind Fred. I just need a strong cup of coffee. It works now. Thanks

BTW. Do you need the * when you type in the units manually. I noticed you don't. Do you insert the units with a keyboard stroke or do you pull down and mouse it in from the pull down menu.

Re: Swap between lbf and lbm

Fred_Kohlhepp — Wed, 10 Jan 2018 18:40:44 GMT

You can type most units; may need "cntrl-Q" twice to get the labels right. (is it a variable, a unit, a constant, a . . .)

Re: Swap between lbf and lbm

ValeryOchkov — Thu, 11 Jan 2018 04:55:28 GMT

When I was at school, I learned that weight (not mass) should not be measured in grams, but in newtons (SI). We went to the store and asked the saleswoman to weigh 5 newtons of sausage!

Re: Swap between lbf and lbm

jdesai-2 — Wed, 10 Jan 2018 20:13:59 GMT

Hmmm. Did Newton get hit in the head with a sausage? I thought it was an apple:)

Re: Swap between lbf and lbm

tietjee — Wed, 10 Jan 2018 21:32:23 GMT

lbm - pounds mass

slug - mass

lbf - pounds force

kg - kilo grams mass

kgf - kilo gram force.

Newton - force

I once had an UK engineer use kg and Newtons in the same sentence, both referring to force (load cell rating). And you thought our system was confusing.

Re: Swap between lbf and lbm

ValeryOchkov — Thu, 11 Jan 2018 05:05:07 GMT

Here must be newtons, dyne, gmf, kgf, lbf, ozf etc not gm, kg, lb, oz etc

We can use this device on Moon too...

I use it in airports! What is more impotent for aircrafts mass or weight of my baggage?