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FPE equation?
- Thread starter wormbobskey
- Start date
I believe it is: 
The momentum of a particle is traditionally represented by the letter p. It is the product of two quantities, the mass (represented by the letter m) and velocity (v):[2]
Whereas: P would be Newtons in most countries but for us Americans it would be ft/lbs of energy. M= Mass(weight/grams) and V=velocity(speed)
And then throw in this:Conversions Table
20 Newton Meters to Foot-pounds Force = 14.7512
900 Newton Meters to Foot-pounds Force = 663.8059
30 Newton Meters to Foot-pounds Force = 22.1269
1000 Newton Meters to Foot-pounds Force = 737.5621
The momentum of a particle is traditionally represented by the letter p. It is the product of two quantities, the mass (represented by the letter m) and velocity (v):[2]
Whereas: P would be Newtons in most countries but for us Americans it would be ft/lbs of energy. M= Mass(weight/grams) and V=velocity(speed)
And then throw in this:Conversions Table
20 Newton Meters to Foot-pounds Force = 14.7512
900 Newton Meters to Foot-pounds Force = 663.8059
30 Newton Meters to Foot-pounds Force = 22.1269
1000 Newton Meters to Foot-pounds Force = 737.5621
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velcoity x velocity x weight (grains) / 450240
eg.
704x704x14.3 = 7087308.8
7087308.8/450240 = 15.7ft/lbs
eg.
704x704x14.3 = 7087308.8
7087308.8/450240 = 15.7ft/lbs
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Simply multiply the weight of the bullet in grains, times the square of the velocity in FPE, and divide that number by 450400. The resulting figure is the energy of the pellet in FPE.
By the way, about 50 different sites have built in calculators to do this, in case you don't have a scientific calculator.
By the way, about 50 different sites have built in calculators to do this, in case you don't have a scientific calculator.
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If you are interested in where that constant came from and why they are sometimes different, I shall explain.
The equation for kinetic energy is the same for any consistent system of units and is as follows:
KE = 1/2 M x V ^ 2
where KE is the kinetic energy, M is the mass of the projectile, and V is the velocity.
In the SI or metric system of units, the mass is in Kilograms, and velocity is in meters per second. In the USCS (United States Customary System) the unit of mass is the slug, and velocity is the familiar feet per second. This is where it becomes a bit complicated since projectiles are given in the weight in grains. Weight and mass are not the same, but on the earth, it is fairly easy to make the conversion since we know the acceleration of gravity.
However, the rounding of the acceleration of gravity is where the constant gets a bit buggered. The more precise value is 32.174 ft/s ^ 2, however it is often rounded to 32.2 ft/s ^ 2.
To make the conversion you must first get the weight in grains to weight in pounds. That is simply there are 7000 grains in one pound. So, you first divide the weight in grains by 7000 and that gives you the weight in pounds.
Now the next step is to convert the weight in pounds to the mass in slugs. This is where you use the acceleration of gravity. A mass of one slug will essentially weigh 32.174 pounds on the earth. The actual weight will vary a small amount depending where you are on the earth, but the 32.174 pounds is regarded as standard. Therefore, the next step is to divide the weight of the pellet in pounds by 32.174. If you use the rounded 32.2 (or some other rounding) you will get a slightly different value. But, for all practical purposes, this small difference is usually less than the variability of chronographs.
Finally, you need to get the 1/2 in there so divide that mass by 2. Then multiply that small amount by the square of the velocity for the final kinetic energy.
What I usually put into my calculator is the following: wt / 7000 / 32.174 / 2 x V ^ 2 = KE. I do it this way because I have the conversions memorized rather than the 450,436 constant.
The equation for kinetic energy is the same for any consistent system of units and is as follows:
KE = 1/2 M x V ^ 2
where KE is the kinetic energy, M is the mass of the projectile, and V is the velocity.
In the SI or metric system of units, the mass is in Kilograms, and velocity is in meters per second. In the USCS (United States Customary System) the unit of mass is the slug, and velocity is the familiar feet per second. This is where it becomes a bit complicated since projectiles are given in the weight in grains. Weight and mass are not the same, but on the earth, it is fairly easy to make the conversion since we know the acceleration of gravity.
However, the rounding of the acceleration of gravity is where the constant gets a bit buggered. The more precise value is 32.174 ft/s ^ 2, however it is often rounded to 32.2 ft/s ^ 2.
To make the conversion you must first get the weight in grains to weight in pounds. That is simply there are 7000 grains in one pound. So, you first divide the weight in grains by 7000 and that gives you the weight in pounds.
Now the next step is to convert the weight in pounds to the mass in slugs. This is where you use the acceleration of gravity. A mass of one slug will essentially weigh 32.174 pounds on the earth. The actual weight will vary a small amount depending where you are on the earth, but the 32.174 pounds is regarded as standard. Therefore, the next step is to divide the weight of the pellet in pounds by 32.174. If you use the rounded 32.2 (or some other rounding) you will get a slightly different value. But, for all practical purposes, this small difference is usually less than the variability of chronographs.
Finally, you need to get the 1/2 in there so divide that mass by 2. Then multiply that small amount by the square of the velocity for the final kinetic energy.
What I usually put into my calculator is the following: wt / 7000 / 32.174 / 2 x V ^ 2 = KE. I do it this way because I have the conversions memorized rather than the 450,436 constant.
Upvote 0