ft/lbs (ugh) vs ft-lb muzzle energy

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I must confess I have been GUILTY of the OP's assertion however I must point out that I am not usually intending to write a "Scientific Dissertation" with my posting to any forum but rather engage in more or less CASUAL technical conversation which is not intended to be submitted to the board of regents for grading! :p

Perhaps the OP might make a better impression here if he introduces himself and gets to know the community rather than jumping in on his first post with corrections to terminology commonly used by the majority of the current membership. :)
 
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I agree with the original poster.

Details matter, simple as that.

Making up words to be politically correct, adding letters to a word, for what-ever silly reason, using the wrong term for an item,etc., etc.

Again, details DO matter.



Mike

P.s.- And what I DO NOT understand, is when you send a private note to attempt to help a person correct his or her ways, they get all uppity. Not all, but some take being wrong...personally. Funny thing...they should..!
 
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Now I know why my gun was off!!



Just kidding here. This reminds of when I got back in to dirt bike riding several years ago. When I was younger, everyone would say, "I jumped my bike." but the kids now day say, "I ramped my bike" which bugs me. However, I understand what they mean and I don't try to correct them on how I think they should talk. That would be rude.
 
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It actually took me reading through the OP a few times to fully understand what he was talking about. I usually abbreviate using FPE, but I do agree with what you are saying. If you are talking unit of measurement, they matter. ft-lb for energy, lb-ft for torque.

I also get bothered when I see energy and power used interchangeably. Where energy is a measure of force over distance, power is a measure of energy over time. Just in case you want to measure how many actual Watts of power you airgun is putting out. 
 
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k9rfz, "Maybe I expected too much from this forum's members" ?!? What a nice, congenial way to connect with people on your very first post. I get what you're saying about correct technical terminology but more importantly WE all get what EACH OTHER are saying & meaning when we post here. Having expectations are just disappointments waiting to happen. Sorry you had them (expectations) & weren't able to let the ft/lbs vs ft-lbs thing go. As far as I know, we're having a conversation in type on this forum, NOT writing a technical manual. I mean, what's next? Picking apart our grammar? Unpucker your sphincter, get into the camaraderie & giving attitude of us dumb clodhoppers & maybe learn something new about this sport/hobby (oops, sorry. That should have been sport-hobby). Get into the intent or gyst of the conversation & don't worry about all the rite wurdz! Welcome aboard!!!
 
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Please re-read my previous two posts in this thread and point out where I criticized commenters on this forum for inappropriate use of ft/lbs. My criticism was directed at authors who are writing published reviews and vendors selling air guns who get paid for their effort. THEY should get the terminology correct and set an example for others. I appreciate the few civil commenters on this thread who recognized the validity of my point. As to the others who took my comments as a personal offense and replied with snarky and derisive comments; you are welcome to your opinions. WARNING: THE FOLLOWING STATEMENTS MAY CAUSE COGNITIVE DISSONANCE FOR SOME READERS. For a group that strives for accuracy in shooting, why do you condone and defend sloppy inaccurate use of terminology? When did doing the correct thing become a maligned habit in America?

I do hope some members learned the correct units for muzzle energy from this post and will become aware of the prevalent misuse of ft/lbs. I was reading the specs on an air rifle on the PyramydAir website just this morning and saw it expressed as 23.4 ft/lbs. If anyone from Pyramyd Air is reading this post, maybe you would convince your web manager to do a global replace of ft/lbs with the correct ft-lb (or FPE) units across the site. 
 
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I, and most others use FPE or fpe (Foot-Pounds-Energy). I don't use ft/lb or ft-lb when referring to kinetic energy. The AAFTA handbook mostly uses fpe but also uses ft/lb and foot-pounds in a couple of instances. But I can tell what it's intended to mean based on the context of it's use.

I have more concern when someone tries to include the acceleration of gravity into the FPE equation, and then comes up with a conversion constant that is ALMOST correct. Gravity is NOT part of the equation, but that slightly erroneous conversion is still commonly used. Does it really matter? - not usually, but it is irritating to see.
 
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I remember years ago at a lecture; Buckminster Fuller asked an audience of scientists if anyone would disagree with the fact that the sun rises every morning. No one disagreed. He then went on to point out that the sun does not rise and explained it in regards to the earth's rotation, etc., etc., etc.

It was a valid point, but I really don't believe that any of the scientists in attendance were under the impression that the sun rises. It's just an expression we all use.

In the case of ft-lbs and ft/lbs, though only one way is technically correct, I like to think that we all understand the intent.
 
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Scotchmo, you have run up against one of the peculiarities of the US system of units. The formula for kinetic energy (muzzle energy) uses mass as an input, but we weigh things in pounds which are a unit of force. So pounds have to be converted to mass units (slugs) before entering into the formula for kinetic energy. This is done by dividing pounds by the gravitational constant "g". This is why you may have seen a muzzle energy formula with "g" in it.

In any case, the exact constant you see online for calculating muzzle energy will depend on what value of "g" was used to determine it.

For g = 32.1 ME constant = 448,000

For g = 32.2 ME constant = 450,800

I hope that helps. And yes, it is irritatingly confusing.
 
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Scotchmo, you have run up against one of the peculiarities of the US system of units. The formula for kinetic energy (muzzle energy) uses mass as an input, but we weigh things in pounds which are a unit of force. So pounds have to be converted to mass units (slugs) before entering into the formula for kinetic energy. This is done by dividing pounds by the gravitational constant "g". This is why you may have seen a muzzle energy formula with "g" in it.

In any case, the exact constant you see online for calculating muzzle energy will depend on what value of "g" was used to determine it.

For g = 32.1 ME constant = 448,000

For g = 32.2 ME constant = 450,800

I hope that helps. And yes, it is irritatingly confusing.
Click to expand...

Pellet "weight" is given in grains which is a unit of mass. - i.e. 8.44gr

Kinetic energy = mass/2 x velocity^2

When using imperial units and desiring FPE, the units of mass is slugs, and the units for velocity is feet/second.

Convert the grain to slug:
https://www.google.com/search?client=firefox-b-1-d&q=slug+grain

Than solve the equation as it is written. Gravity was not used.

Scales that we use to "weigh" are calibrated to measure mass. So if you are "weighing" your own pellets to determine mass, than you probably used a scale that came with a reference mass to calibrate it:



Gravity was already accounted for in the scale calibration.
 
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Scotchmo, I see where you are coming from now. The issue is that grains are defined as units of mass. So 7000 grains = 1 lbm and 1 slug = 32.174 lbm, with "g" conveniently included in the definition of the slug.

Giving 1 slug = 7000 * 32.174 = 225,218 grains.

The confusion, maybe mine, involves mixing BG and EE systems of units. Without the slug in the EE system, mass was represented in engineering formulas by lbm/g. So there was one formula for SI units and another when using EE units! If "g" is still cropping up in formulas for muzzle energy it is probably a holdover from that past practice.

In any case, if you are encountering small differences in the muzzle energy constant it must be due to people using slightly different values for "g" instead of the 32.174 that is part of the definition of the slug.

I think this conversation has gone way beyond the point of having general interest. If you want to talk some more, feel free to send a message to my Inbox. Otherwise let's call it good for now.

Chuck
 
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UPDATE 5/29/20:

I contacted the President of the AAFTA more than a year ago and pointed out the inappropriate use of ft/lbs in various tables in their rules handbook. I received a very civil reply and admission to the mistake and a commitment to correct the units in the next revision. Last week, I submitted a notice to Pyramyd Air of the many instances they incorrectly use ft/lbs on their website. Yesterday, I received notice they agree and will have their IT group attempt a global replace to correct the situation. BTW, this earned me a 5% discount coupon on my next purchase from Pyramyd Air. I'll next approach Stephan Archer to suggest similar corrections on his HardAir reviews. In the age of anti-intellectualism and uncivil discourse, a persistent person with a valid point can still make a positive difference.
 
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