MCgunner
Member
Adelbridge, you hunted hogs with a knife???
Common down here in the south, done it myself. Now, google Ben Lily. He hunted black bear with a knife. HE was da man....
Adelbridge, you hunted hogs with a knife???
? Where do you get that from? I just crunched the numbers again on my metric calculator and came up with 6.63624 kg m/s or exactly 48.00173599 lb ft/s. Where on earth did you come up with 0.76? Do you honestly think a 240gr bullet moving at super sonic speed would have less then 1lbs/sec momentum, I would think common sense would be screaming from somewhere.You've discounted the effect of gravity for the ft-lbs calculation (energy) so why not do the same for the momentum calculation? The momentum is 0.76 (lbm-ft)/sec.
I always calculated momentum as: projectile weight x projectile speed / 225,120 = momentum
55 gr. x 3100 / 225,120 = .76 momentum
In my previous example involving arrows, I cited a 400 gr. arrow @ 260 FPS which has 60# KE
400 gr. x 260 fps / 225,120 = .46 momentum
Using my calculation, a 95 gr. bullet @ 875 fps (pocket 380) produces a momentum of .37
A snub 38 special shooting a 130 gr. bullet @ 850 fps = .49 momentum
Kachok said:We are measuring at the muzzle so the g factor if not relevant at all so why bring it up? Mabey if we were talking about shooting 3,000 yards, but there is no such talk here. I still don't see how that could possibly make a notable difference much less reduce 48 lbs ft/s of momentum to .76!
Direct relationship is a mathematical principle with a specific definition.Mass, energy and momentum are not DIRECTLY related.
Again, you don't get to redefine terms that already have well-accepted mathematical definitions.Mass has much more effect on the momentum figure and speed has much more to do with the energy figure although this also means they are all related just not in a direct linear fashion.
When you're talking about mathematics, you can't just come up with terminology out of the blue and pretend it means something specific.I've made up nothing.
People who want to talk about quantities related to and defined by science of physics can't reasonably turn around and complain when people oblige them by talking about physics and physics equations and it's ridiculous to pretend that it's a negative thing to bring those topics into such a conversation.That you decided to take us down a physics equation rabbit hole...
What unit are you using here? Your method seems absurd to me...
Kachok,
Your energy calculation for a 55gr bullet @ 3100fps is as follows:
(55gr*1lb)/7000gr = 0.00786 lbf
k.e. = mass*(velocity^2)*0.5
lbm = lbf*s^2/32.1 ft
k.e. = 0.5*(0.00786 lbf/[(32.1 ft/s)^2])*3100 fps^2 = 1176.1 ft-lb
Your momentum calculation is as follows:
Momentum = mass*velocity
M = (0.00786 lbf/(32.1 ft/s^2))*3100 fps = 0.76 lbm-ft/s
If you place a 55gr bullet on a table, the force it exerts on the table is 55 lbf which is the same as lbm because the force is in the same direction as g. By definition, 1lbf is the force required to give 1lbm an acceleration of 32.1 ft/s^2. If g = 32.1 ft/s^2, then 1lbf = 1lbm.
I'm not talking about mathematics. Again (missed it the first time, did you?) I'm talking about rifle ballistics. Perhaps you think you've wandered into a mathematics forum here?When you're talking about mathematics...I've made up nothing.
Aren't you a caution! First giving me a math (or was it physics?) lesson, and now an English lesson. All in the Rifle Country forum!The general definiton of "primary" doesn't allow such a thing
weight x speed / 225120 = momentum
I got .76 momentum for the 55 gr. @ 3,100 fps
Absurd? See next reply.
theCan said:Momentum is a vector, not a unit. Mass*velocity = momentum. Dividing by 225120 is absurd. Unless you're converting to some unknown unit.
Confusion often comes from the fact that the lb is the imperial unit for both mass and force. One lb (force) = ~32.2 lb (mass) x ft/second^2. 1858 has it right.OK I gotta call BS on this 0.76 lb ft/s thing
Kachok said:So let me get this straight, you are saying that a 1kg mass object rolled at 1m/s speed does not in fact have 1kg m/s momentum? Dude that sounds absolutely insane you know that right?
Yeah I erased that part when I re-read, sorry, but I am still waiting for someone to explain how 6.63624 kg m/s can be less then 1lbs ft/s that makes absolutly no sense at all kg m/s is a much higher unit of messurment.I clearly stated that kg in the S.I. system is a unit of mass and therefore no adjustment for g is required. This is not the case for pounds mass and pounds force in the Imperial system and the specific case of a bullet and its energy in flight.
All you have to do is show a calculation for the kinetic energy of a bullet in flight using the Imperial system and the S.I. system to convince yourself of the difference between kg, lbf and lbm.