nitpicking the community: foot-pound energy symbol

[pedantic]

hi guys,


i see this all the time in posts, videos (i'm looking at you, too, Ted!), and even product pages: "ft/lb"... WHAT IS THAT?


a foot-pound, as you know, is a unit of energy commonly used to express muzzle energy of a projectile.


for the mathematically inclined/curious, energy can be conceptualized in a lot of ways, but one that clearly demonstrates the unit in question is mechanical work.


mechanical work done on an object by a force can be calculated by integrating the force doing work on an object along the path the object is moved by that force.


more simply, it can be expressed as Work = Force * Distance


as an example, if you lift an object weighing two pounds vertically upward with your hand by a distance of five feet, you have expended (2 pounds of force) * (5 feet) = 10 ft*lb of work (a type of energy) in doing so.


from that example and the preceding equation, you may notice that this unit of energy, the foot-pound (or "foot*pound"), cannot be the same as a foot divided by a pound ("foot/pound").


a "ft/lb" would describe a unit of force per unit of distance, which is NOT a unit of energy.


correct symbols for the foot-pound include: ft·lb, ft*lb, ft-lb


sorry for annoying everyone, but as an engineer, i cringe every time i see "ft/lb".




a few relevant links:
https://en.wikipedia.org/wiki/Foot-pound_%28energy%29
https://en.wikipedia.org/wiki/Work_%28physics%29
http://hyperphysics.phy-astr.gsu.edu/hbase/work2.html

 

[pedantic]

while i'm on a roll here, carbon dioxide is CO2, not C02.

see the difference: a molecule of CO2 is one atom of carbon (the atomic symbol is the letter "C") bonded to two atoms of oxygen (the atomic symbol = the letter "O", not the number zero ("0")).

it's spelled incorrectly, among other places, in the forum title: http://airgunnation.dev/forum/discussion/springers-pumpers-and-other-airguns/

ok, i think i'm done now. sorry

 

[ztirffritz]

I'm glad you got that out of your system. 

 

[ChrisLJ]

And some folks are bugged by a poster who doesn't use capitalization. People sure can be silly, eh?

 

[Stone02]

I believe that another term, commonly used, is fpe ( ft-lb energy).

 

[Michael]

I like to keep it simple FPE

 

[Matt_Dubber]

Hahaha! Thank you pedantic for clearing that up
Agree with you Michael, FPE is nice and simple

Matt

 

[Ginuwine1969]

Hey Matt, have you found any pellets that shoot well on low power on you're 510?

 

[pedantic]

yeah, FPE is another legit one

 

[pedantic]

"ChrisLJ"And some folks are bugged by a poster who doesn't use capitalization. People sure can be silly, eh?

haha

 

[Stone02]

Capitalization for acronyms ceases when accepted in common use, like laser, radar and fpe.

 

[Zephyr]

Said with a BIG grin (capitalisation as emphasis not signifying an acronym!), and tongue firmly in cheek... 
Capitalisation NOT Capitalization.

TeeHee

 

[billydjann]

I understand your frustration on this matter...
But what bothers me even more than this is People at Walmart or any store visiting each other 
and will not move aside ... blocking aisles

Only kidding..... Thanks for the very good education...
I never thought about it before this..... 

 

[ChrisLJ]

You had me going for a moment there Zephyr, and I had to look it up. It appears it's one of those words that can use either spelling, but it would have been a funny catch. What really annoys me is when I make a goofy mistake misusing a word, such as "bear" instead of "bare". I guess as long as we can get our point across it's all good, but the internet sure seems to amplify all of the errors of people and the many self-correcting gizmos we rely on. 

 

[BRS]

 

[travels4fun]

There is always the European way of expressing muzzle energy in Joules.

 

[Bruce]

I guess someone on here has to be politically correct.

 

[pretbek]

"travels4fun"There is always the European way of expressing muzzle energy in Joules.

If by European you mean "the whole world except Liberia, Burma and the USA" then yes, Joules is how they express energy.

And here in the US I still write fpe. 

 

[pedantic]

yeah, the Joule (symbol: J) is the SI unit of energy. it's what we mostly use in science.

just a little fun: about how many shots' worth of muzzle energy would it take to bring a room temperature can of soda to a boil (assuming all of the energy could be perfectly transferred into the liquid)?

let's say my fx royale 400 .22 is shooting jsb 18.13gr pellets at 900ft/s

using the formula for kinetic energy: energy = 1/2 * (mass) * (velocity)^2, and some unit conversion, we get 32.6 ft-lb muzzle energy. this is equal to 44.2 J.

https://www.google.com/search?q=1%2F2+*+%2818.13+grain%29+*+%28900+ft%2Fs%29^2+in+lbf*ft

next, the change in temperature of water can be related to an energy input:
energy added (in J) = (volume of water (in mL)) * (4.186 J / (mL of water * °C of change)) * (temperature change)
see: http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/spht.html

saying that room temperature is 20 °C and that water boils at 100 °C, that's a temp change of 80 °C
a can of soda (which is mostly water) is 12 fl oz = 355 mL

so: 355 mL * 4.186 J/(mL*°C) * 80 °C = 118,882.4 J is how much energy it takes to boil a can of soda

dividing that by our muzzle energy, we get:
118,882.4 J / 44.2 J = 2690

it would take 2690 shots' worth of muzzle energy to bring a room temperature can of soda to a boil.

water has a very high specific heat capacity (compared to other substances (like oil), it takes a lot of energy to heat up water).

think about that next time you boil a cup of water for coffee. you're shooting it like 3000 times.

 

[HauntedMyst]

We need a new system since none of them work for airguns. Joules just sounds silly. Foot pound is equally ridiculous and Feet Per Second is equally useless without other data. 

I suggest a new system called AKA - @ss Kicking Ability

@KA Level 1 Squirrel
@KA Level 2 Raccoon
@KA Level 3 Pig
@KA Level 4 Deer
@KA Level 5 Moose
@KA Level 6 Elephant
etc...
@KA Level 20 Hiroshima