Nightcrawler
New member
I've repeatedly heard muzzle energy of firearms, as well as recoil energy, measured in something called a "foot-pound" instead of the usual measurment unit for enery, Joules. What exactly is a foot pound?
Pardon my ignorance...what is a foot-pound?
- Thread starter Nightcrawler
- Start date
Isn't it the amount of energy needed to lift 1 pound 1 foot straight up, or something like that?
I think joules is electricity. I know a heart defibrilator is charged to a certain number of joules before use.
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"Anyone feel like saluting the flag which the strutting ATF and FBI gleefully raised over the smoldering crematorium of Waco, back in April of ‘93?" -Vin Suprynowicz
[This message has been edited by deanf (edited November 01, 2000).]
I think joules is electricity. I know a heart defibrilator is charged to a certain number of joules before use.
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"Anyone feel like saluting the flag which the strutting ATF and FBI gleefully raised over the smoldering crematorium of Waco, back in April of ‘93?" -Vin Suprynowicz
[This message has been edited by deanf (edited November 01, 2000).]
BadMedicine
Moderator
That's when you take the flat side of your foot, and repeatedly pound it against a democrat, or BATF agent. 
Pardon my corniness
It's the method of measureing the pressure (punch) created by projectiles at different velocities.
I'm not real sure excactly how they measure it, I think it's the overall wieght excerted on a foot round area around the bullet (ie 6" on each side, all the way around.)
Am I right? am I? am I? I think that's what it is.
Pardon my corniness It's the method of measureing the pressure (punch) created by projectiles at different velocities.
I'm not real sure excactly how they measure it, I think it's the overall wieght excerted on a foot round area around the bullet (ie 6" on each side, all the way around.)
Am I right? am I? am I? I think that's what it is.
BadMedicine
Moderator
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by deanf:
Isn't it the amount of energy needed to lift 1 pound 1 foot straight up, or something like that?
[/quote]
No. Because guns produce hundreds if not thousands of foot/pounds at the muzzle. If you put even 100lbs on your un and pulled the trigger?? That's right..it'd blow up.
Isn't it the amount of energy needed to lift 1 pound 1 foot straight up, or something like that?
[/quote]
No. Because guns produce hundreds if not thousands of foot/pounds at the muzzle. If you put even 100lbs on your un and pulled the trigger?? That's right..it'd blow up.
Munro Williams
New member
A foot pound is the amount of force needed to move one pound one foot. I think.
TearsOfRage
New member
Foot-pounds can be used as a measure of torque (force applied at a certain distance from a central axis time the distance from that axis), but in regards to firearms effectiveness, it is a measure of energy.
work (another word for energy) = force times distance
One foot pound is the energy required to exert a force of one pound (the weight of a one pound object) to move an object one foot.
This is often described as the energy required to lift a one pound object one foot,
because the energy require to move it horizontaly would vary depending on friction etc.
In a firearm, of course, the energy is used to accellerate the bullet, rather than moving it against a fixed resistance.
A Joule is also a measure of energy, but it does not have to be electrical.
1 foot-pound = 1.35582 Joules
TOR
work (another word for energy) = force times distance
One foot pound is the energy required to exert a force of one pound (the weight of a one pound object) to move an object one foot.
This is often described as the energy required to lift a one pound object one foot,
because the energy require to move it horizontaly would vary depending on friction etc.
In a firearm, of course, the energy is used to accellerate the bullet, rather than moving it against a fixed resistance.
A Joule is also a measure of energy, but it does not have to be electrical.
1 foot-pound = 1.35582 Joules
TOR
Mike Irwin
Staff
I thought pound-feet was a measure of torque... 
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Smith & Wesson is dead to me.
If you want a Smith & Wesson, buy USED!
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Smith & Wesson is dead to me.
If you want a Smith & Wesson, buy USED!
All right, people, don't make me bring Art in here to straighten this out... 
Energy = Mass X (Velocity)(Velocity)
We measure energy by expressing it as the amount of force needed to moved a given mass over a given distance.
Metrically, we have the newton (1 kg accelerated 1 m/s/s). In English measurement, we have the foot pound, already defined, above. They used to even use a unit called the "slug," but I'm not remembering off-hand how that one comes out.
Bad Medicine-- pressure, expressed as mass per square area, is not really applicable, here. The pressures of a 16" battleship cannon are far lower than those in my .300 Win Mag, but which would you say has more energy?
(Hint, one throws a 180g bullet at 3100 fps, the other throws a 1,200 pound (that's 8,400,000g, btw) projectile at about 2600 fps.) Although one can surely measure the energy expelled when a cartridge charge is burned, the energy we usually think of in "ballistics" (which means, literally, "the study of falling objects, and has nothing to do with propulsion) is that of the projectile at a given point in it's flight-- muzzle, midrange, or downrange.
Energy is an interesting checkpoint, but is not the end-all, be-all. E=MV(squared) means that as the velocity increases, the energy increases geometrically. The .308 150 g load has far more energy at the muzzle than a 1 oz 12-ga slug, but which do you think really has more knock-down power? Momentum, which is Mass X Velocity, is a better indicator than Energy, and things like frontal area of the projectile and Sectional Density are very important, too.
Energy = Mass X (Velocity)(Velocity)
We measure energy by expressing it as the amount of force needed to moved a given mass over a given distance.
Metrically, we have the newton (1 kg accelerated 1 m/s/s). In English measurement, we have the foot pound, already defined, above. They used to even use a unit called the "slug," but I'm not remembering off-hand how that one comes out.
Bad Medicine-- pressure, expressed as mass per square area, is not really applicable, here. The pressures of a 16" battleship cannon are far lower than those in my .300 Win Mag, but which would you say has more energy?
(Hint, one throws a 180g bullet at 3100 fps, the other throws a 1,200 pound (that's 8,400,000g, btw) projectile at about 2600 fps.) Although one can surely measure the energy expelled when a cartridge charge is burned, the energy we usually think of in "ballistics" (which means, literally, "the study of falling objects, and has nothing to do with propulsion) is that of the projectile at a given point in it's flight-- muzzle, midrange, or downrange. Energy is an interesting checkpoint, but is not the end-all, be-all. E=MV(squared) means that as the velocity increases, the energy increases geometrically. The .308 150 g load has far more energy at the muzzle than a 1 oz 12-ga slug, but which do you think really has more knock-down power? Momentum, which is Mass X Velocity, is a better indicator than Energy, and things like frontal area of the projectile and Sectional Density are very important, too.
Apple a Day
New member
Reason #45612 why metric units are better then the crap we use:
A foot pound is a unit of work in the old Imperial system, while the Joule is the metric equivalent.
It is also a unit of torqe. THe difference is that if the force and the distance it moves are parallel then it is a measurement of work (work is force times distance). If you are calculating torque then you multiply the force you exert by the perpendicular distance from the force to the center of rotation- also pounds times feet. The difference is that in one, quantities are parallel while in the other they are perpendicular. The metric units of torque are newton*meters.
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Those who use arms well cultivate the Way and keep the rules.Thus they can govern in such a way as to prevail over the corrupt- Sun Tzu, The Art of War
A foot pound is a unit of work in the old Imperial system, while the Joule is the metric equivalent.
It is also a unit of torqe. THe difference is that if the force and the distance it moves are parallel then it is a measurement of work (work is force times distance). If you are calculating torque then you multiply the force you exert by the perpendicular distance from the force to the center of rotation- also pounds times feet. The difference is that in one, quantities are parallel while in the other they are perpendicular. The metric units of torque are newton*meters.
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Those who use arms well cultivate the Way and keep the rules.Thus they can govern in such a way as to prevail over the corrupt- Sun Tzu, The Art of War
Whups! Jim, you're ABSOLUTELY correct. But this proves my point still further-- mass is far less significant than energy in the equation.
Torque, by its nature, will be a measure of force over a distance.
We have to use foot pounds to stay consistant with our measure of velocity (fps) and weight (1 lb. = 7000 grains).
If we ever get to where we're measuring my .300 Win Mag's MV as 1000m/s, and measure the bullet in grams, THEN we'll be getting somewhere!
--L.P.
Torque, by its nature, will be a measure of force over a distance.
We have to use foot pounds to stay consistant with our measure of velocity (fps) and weight (1 lb. = 7000 grains).
If we ever get to where we're measuring my .300 Win Mag's MV as 1000m/s, and measure the bullet in grams, THEN we'll be getting somewhere!
--L.P.
Mike Irwin
Staff
Hey LongPath, as an aside...
Those are the lightest 16" shells I've ever seen...
Standard AP shell for the 16"/50 Mk 7 naval rifle used on the Iowa class was 2,700 pounds, or nearly 19 million grains.
Breech pressure with a standard 660-lb. powder charge and the 2,700 AP shell was about 18.5 tons per sq. inch, or about 37,000 psi. Certainly lower than some cartridges, but still up there.
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Smith & Wesson is dead to me.
If you want a Smith & Wesson, buy USED!
Those are the lightest 16" shells I've ever seen...
Standard AP shell for the 16"/50 Mk 7 naval rifle used on the Iowa class was 2,700 pounds, or nearly 19 million grains.
Breech pressure with a standard 660-lb. powder charge and the 2,700 AP shell was about 18.5 tons per sq. inch, or about 37,000 psi. Certainly lower than some cartridges, but still up there.
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Smith & Wesson is dead to me.
If you want a Smith & Wesson, buy USED!
Fire the .357 round with a plasma rifle or a rail gun. Hot plasma punches right though, or, the somewhat-lower-tech rail gun accelerates the projectile to 56,385 fps, giving a muzzle energy of 881,000 ft-lbf with a 125gr round.
If doing the latter, make sure your tripod is well-mounted in concrete.
If doing the latter, make sure your tripod is well-mounted in concrete.
Art Eatman
Staff in Memoriam
First off, go find a high school physics book...
The term "mass", m, in the equations for work, momentum and energy, involves the acceleration due to gravity--"g". On earth, of course, it's 32.16 ft/sec/sec.
The term "slug" is the weight in pounds divided by g. Another term is "poundals"; same as slug.
So, Kinetic Energy = 1/2 times the mass in slugs, times the square of the velocity. The mass, m, of a bullet is the weight in grains divided by 7,000 (to get pounds) and then divided by g.
And, yes, torque is measured in foot-pounds. Horsepower is Torque times RPM divided by 5,252.
, Art
The term "mass", m, in the equations for work, momentum and energy, involves the acceleration due to gravity--"g". On earth, of course, it's 32.16 ft/sec/sec.
The term "slug" is the weight in pounds divided by g. Another term is "poundals"; same as slug.
So, Kinetic Energy = 1/2 times the mass in slugs, times the square of the velocity. The mass, m, of a bullet is the weight in grains divided by 7,000 (to get pounds) and then divided by g.
And, yes, torque is measured in foot-pounds. Horsepower is Torque times RPM divided by 5,252.
, ArtRon Ankeny
New member
And I thought teaching physics and Principles of Technology to high school kids was tough...
Force, work, and energy are all different, but closely related. Like the guys said, a foot pound is the work required to move one pound of mass one foot. If you are into prime movers and the like then you will recognize the unifying equation of W=FxD where W=work, F=Force, and D=Distance. Since we measure force in pounds and distance in feet we come up with lb. ft. or foot-pounds. No, pound-feet and foot-pounds are not the same thing.
In the "metric system" the unit of measure for force is the newton and the unit of measure for distance is the meter. So if W=FxD we come up with newton-meters. By definition 1 newton-meter=1 joule so mechanical work can be measured in joules as well as newton-meters.
In mechanical rotational systems work=Torque x theta (the angle of rotation measured in radians). Torque is equal to the Force (pounds) times the length of the lever arm (feet). Therefore, the unit of measurement for torque is also pound-feet. To find the work done you multiply the torque times the angle moved through and the radians are dropped resulting once again in pound-feet. So, how the hell do you tell the difference between torque and work? That's easy, the unit of measurement for torque is lb. ft. and the unit of measurement for work is ft. lb.
Joules are also units of measurement for electrical work. The unifying equation for electrical work is work = voltage difference (volts) x charge moved (coulombs). Further, a volt x coulomb just happens to be a joule. The concept of a joule is very handy for converting from mechanical to electrical work. For instance you can figure how many joules of electrical work go into your Warn winch on the trusty old 4x4 and how many joules of work go into moving the tree you are skidding out of the woods. Divide the work out (tree) by the work in (winch) and you get the efficiency rating of the winch.
Force, work, and energy are all different, but closely related. Like the guys said, a foot pound is the work required to move one pound of mass one foot. If you are into prime movers and the like then you will recognize the unifying equation of W=FxD where W=work, F=Force, and D=Distance. Since we measure force in pounds and distance in feet we come up with lb. ft. or foot-pounds. No, pound-feet and foot-pounds are not the same thing.
In the "metric system" the unit of measure for force is the newton and the unit of measure for distance is the meter. So if W=FxD we come up with newton-meters. By definition 1 newton-meter=1 joule so mechanical work can be measured in joules as well as newton-meters.
In mechanical rotational systems work=Torque x theta (the angle of rotation measured in radians). Torque is equal to the Force (pounds) times the length of the lever arm (feet). Therefore, the unit of measurement for torque is also pound-feet. To find the work done you multiply the torque times the angle moved through and the radians are dropped resulting once again in pound-feet. So, how the hell do you tell the difference between torque and work? That's easy, the unit of measurement for torque is lb. ft. and the unit of measurement for work is ft. lb.
Joules are also units of measurement for electrical work. The unifying equation for electrical work is work = voltage difference (volts) x charge moved (coulombs). Further, a volt x coulomb just happens to be a joule. The concept of a joule is very handy for converting from mechanical to electrical work. For instance you can figure how many joules of electrical work go into your Warn winch on the trusty old 4x4 and how many joules of work go into moving the tree you are skidding out of the woods. Divide the work out (tree) by the work in (winch) and you get the efficiency rating of the winch.