Suspension of Disbelief

[blainepoe]

I watched that movie "Shoot'em Up" with Clive Owen and Paul Giamatti and he has a round between each of his fingers holding it under a bathroom hand dryer and shoots Giamatti ...that was the end of the movie for me - how stupid?

I think the easiest example is all of the space movies and giant loud explosions in space that would not exist in a vacuum . I generally don't let it stop me from enjoying a movie, but sometimes it does...

 

[Pami]

My biggest complaint was that the movies lied to me about what a suppressor sounds like. I couldn't find one that makes that laser sound anywhere!

*blinks*

They don't go "pew pew" ??

 

[bigg cheese]

ROFL!

Made me think of MoonRaker... Thanks

 

[INRanger]

Yep, basic physics, If the guy getting shot moved backwards 4 feet then the guy shooting the gun would also be moved back 4 feet when he pulled the triger.

Thats not basic physics, thats not even physics. If I shove you we don't both fly backwards. When a gun is fired there is a chemical reaction inside the cartridge resulting in an explosive release of energy. This energy reacts equally and oppositely by propelling the catridge and recoiling/cycling the weapon. When the projectile hits the target it transfers it's energy to the target who enacts its equal and opposite reaction by fragmenting, deforming and ultimatly stopping said projectile. The physical force delivered by the projectile is completly seperate to the force that launched said projectile. If you were joking then my bad.

 

[HandK]

Thats not basic physics, thats not even physics. If I shove you we don't both fly backwards. When a gun is fired there is a chemical reaction inside the cartridge resulting in an explosive release of energy. This energy reacts equally and oppositely by propelling the catridge and recoiling/cycling the weapon. When the projectile hits the target it transfers it's energy to the target who enacts its equal and opposite reaction by fragmenting, deforming and ultimatly stopping said projectile. The physical force delivered by the projectile is completly seperate to the force that launched said projectile. If you were joking then my bad.

Ok so the basic physics rule of for every action there is an opposite and equal reaction just does not stand ture in your universe ? and yes I cant spell. LOL
the fact of the matter is most people wont even know they have been shot when it happens, not untill the gun fight is over and the adrenalin stops flowing does the pain set in and you know you have been hit, barring a spinal cord hit or head shot or breaking a bone. you explane how some semi autos help reduce felt recoil but have you ever shot a double rifle? the felt recoil is the same as ft lbs of energy at the muzzle from the bullet.

 

[INRanger]

Ok so the basic physics rule of for every action there is an opposite and equal reaction just does not stand ture in your universe ? and yes I cant spell. LOL
the fact of the matter is most people wont even know they have been shot when it happens, not untill the gun fight is over and the adrenalin stops flowing does the pain set in and you know you have been hit, barring a spinal cord hit or head shot or breaking a bone. you explane how some semi autos help reduce felt recoil but have you ever shot a double rifle? the felt recoil is the same as ft lbs of energy at the muzzle from the bullet.

You are applying equal and opposite reaction to two separate events. The firing of the projectile and the impact of said projectile. The amount of force applied to the projectile and the weapon is indeed the same but the amount of force said projectile applies is a separate physical interaction. The force applied to impact of projectile is a matter of wt x vel and has no bearing on the amount of energy that the firing applied to the firearm. They are separate. The M-107 Barrett does not recoil at 2910fps the speed the bullet travels. Nor does said recoil exert equal energy to the shooter as the round does on impact. Even if you removed the brake an disabled the buffer the energy would still only be equal to the energy used to set the round on a coarse of acceleration. The central energy that is acting on both the bullet and the rifle is the same the effects are not. The bullet is free to move to the extent of the applied energy the rifle is not. The central energy is diffused at a much greater rate by the resistance of wieght that the rifle/shooter applies. The bullet on the other hand wieghing much less and having a path of least resistance to utilze is afforded more velocity from the same energy there by increasing the amount of stored energy for it to deliver. As an NRA insructor I'm sure you know that the muzzle velocity is not the same as max velocity. As for the actual effects of a shooting we do not disagree I've been hit and I did not feel the first one. The one that hit my hip on the other hand got my imediate attention. sorry for the lengthy post. Besides how could I pass up the opportunity to show the non nuckle dragging side that resides in every Ranger.

 

[dburkhead]

Thats not basic physics, thats not even physics. If I shove you we don't both fly backwards. When a gun is fired there is a chemical reaction inside the cartridge resulting in an explosive release of energy. This energy reacts equally and oppositely by propelling the catridge and recoiling/cycling the weapon. When the projectile hits the target it transfers it's energy to the target who enacts its equal and opposite reaction by fragmenting, deforming and ultimatly stopping said projectile. The physical force delivered by the projectile is completly seperate to the force that launched said projectile. If you were joking then my bad.

Um, sorry but no.

One of the results of Newtons Third Law is conservation of momentum. Force over time is momentum. Another (more common) way to describe momentum is mass times velocity (as opposed to energy which is 1/2 mass times velocity squared). The Force that pushes a bullet down the barrel of a gun is equaled by the force pushing the gun backwards (recoil) and over the time that the bullet is in the barrel produces a recoil of the gun. Actually, the recoil momentum of the gun is slightly greater than the momentum of the bullet since the recoil of the gun is recoil momentum of bullet + muzzle blast.

So we have recoil of gun > momentum of bullet.

What would move a person struck by a bullet is momentum. That's what momentum is--"quantity of motion." Between the time the bullet left the gun and the time it strikes the target it has slowed down due to air drag. So the momentum at the point of impact will be less than at the muzzle so we have:

recoil of gun > momentum of bullet at muzzle > momentum of bullet at target.

After the impact with the target the total momentum must be the same--any remaining momentum of the bullet (whether it remains in the target and is moving with it) plus any momentum of the target must be exactly the same as the sum of the momenta of bullet and target before the impact. Since the bullet is not going to stop dead and drop straight to the ground, nor is it going to "rebound" in an elastic fashion from a human target the momentum imparted to the target will be less than that of the incoming bullet. So we have:

recoil of gun > momentum of bullet at muzzle > momentum of bullet at target > momentum imparted to the target.

Thus, if the bullet has enough momentum to knock the target flying, the gun would have enough recoil back in the other direction to knock the shooter flying. Now, it might be that a shooter being well balanced and "braced" could withstand without falling a level of recoil that would knock someone who's off balance and not well balanced over (for much the same way that I, as a brown belt in Judo, could throw/knock over most people using techniques that put them off balance while allowing me to keep my balance), however what is shown in many movies, of people being thrown through the air, over furniture, and what have you is patently absurd.

Let's do some numbers.

One typical .30-06 bullet has a muzzle velocity of 760 m/s and a mass of 14 g (that's .014 kg). (Oh, metric units because the math is easier that way.) The momentum, then is 10.6 kg-m/s. Suppose all that momentum is "dumped" into a human body at impact (this would require a pretty magical bullet to avoid overpenetration, but let's go with it as a "best case"). For an 80 kg human being, that would lead to a velocity of 13.2 cm/s. A typical walking speed is about 3 MPH or about 134 cm/s, more than ten times the speed that would be imparted by the bullet.

That bullet isn't going to move you anywhere.

 

[dburkhead]

You are applying equal and opposite reaction to two separate events. The firing of the projectile and the impact of said projectile. The amount of force applied to the projectile and the weapon is indeed the same but the amount of force said projectile applies is a separate physical interaction. The force applied to impact of projectile is a matter of wt x vel and has no bearing on the amount of energy that the firing applied to the firearm. They are separate. The M-107 Barrett does not recoil at 2910fps the speed the bullet travels. Nor does said recoil exert equal energy to the shooter as the round does on impact. Even if you removed the brake an disabled the buffer the energy would still only be equal to the energy used to set the round on a coarse of acceleration. The central energy that is acting on both the bullet and the rifle is the same the effects are not. The bullet is free to move to the extent of the applied energy the rifle is not. The central energy is diffused at a much greater rate by the resistance of wieght that the rifle/shooter applies. The bullet on the other hand wieghing much less and having a path of least resistance to utilze is afforded more velocity from the same energy there by increasing the amount of stored energy for it to deliver. As an NRA insructor I'm sure you know that the muzzle velocity is not the same as max velocity. As for the actual effects of a shooting we do not disagree I've been hit and I did not feel the first one. The one that hit my hip on the other hand got my imediate attention. sorry for the lengthy post. Besides how could I pass up the opportunity to show the non nuckle dragging side that resides in every Ranger.

The "two separate events" are connected. It's not velocity that is conserved, but momentum. And the momentum, is (at best) the same at both ends of the bullet's travel (actually, it's a bit less at the far end). Energy is a red herring since it's momentum that moves things, not energy. They're linked because they both derive from mass and velocity, but they are not the same. This is why (other things being equal) a light, high velocity round recoils less than a heavy, slow round of the same muzzle energy.

The peak force may be higher at the point of impact but that higher force happens over a shorter time. And since it's force over time that causes motion the shorter time cancels out the higher force.

It all comes down to conservation of momentum which is absolutely the most well established of all physical laws (yes, even beating out the 2nd law of thermodynamics).

Note that I don't play a physicist on TV, but I am one in real life.

 

[HandK]

I could'nt have said it better my self!! No really I could'nt, LOL

 

[bigg cheese]

How did we go from "Dang, aren't movies fake?" to "Nuh-uh, here's my science!"

hahaha.

 

[cce1302]

Thats not basic physics, thats not even physics. If I shove you we don't both fly backwards.

All things being equal, yes, you do. If both are of equal mass and are braced/supported the exact same way, both will move apart exactly the same. Why this is not true in practice is because the "shover" is smart enough to catch the "shove-ee" off balance, or at least not braced against the push. If you want to see what would happen with all things being (nominally) equal, get a friend of the same height & weight that you are, stand with your feet shoulder width apart facing each other, and try pushing. you'll both fall back equally.

And Reps to Dburkhead. Even if I thought you were wrong, I couldn't respond to your science.

 

[INRanger]

Ouch dbukhead you are the James Bond of geekdom! Before I responded to this I sent my high school science teacher an e-mail and apologized for sleeping so much. That was educational, apparently poorly remembered high school science x SOTIC instructor = guy with foot in mouth. The shoving anology made a lot more sense late last night, but I think its still a fair anology for firing a firearm.(not the best)

 

[IndyBeldar]

When you're knowledgeable about what weapons really can and can't do, it turns a lot of action movies into comedies. I remember "Rambo" (the sequel to "First Blood") was a laugh riot around the barracks.

 

[dross]

I've always been able to put aside the silly weapons stuff, but for some reason the mistakes in Army movies always gets me. How hard is it to find someone to explain where the ribbons go, or that First Sergeants and Sergeant's Major don't get called "Sarge" by anyone.

 

[antsi]

The firing of the projectile and the impact of said projectile. The amount of force applied to the projectile and the weapon is indeed the same but the amount of force said projectile applies is a separate physical interaction. The force applied to impact of projectile is a matter of wt x vel and has no bearing on the amount of energy that the firing applied to the firearm.

Um, no.

The M-107 Barrett does not recoil at 2910fps the speed the bullet travels.

That's because the rifle is just a skoshe more massive than the projectile. The total momentum is the same on both ends.

PS - Oops, didn't read the whole thread. What Dburkhead said.

 

[SWAT-DOC]

Don't forget the "noisy cricket" in Men in Black...now that one I would believe...action=reaction.

 

[rw65hdd]

This post has everything, Army, Jolie, Arnie, Sly, Science class, Physics class, Etc. I learned more from this thread on more topics than any thread I have looked at in my 44yrs. This site is soo cool. I really did enjoy the lesson. I am not sure I have it all yet and will have to verify what was said but If I stay at holiday inn express tonite I should be able to understand. Great job guys

PS- I just had to go put on pants in case that one guy is really looking at me through the pc screen.

 

[whiskeytangofoxtrot]

I won't even watch the movie, "The Rock", because it is completely bogus on everything. Plus Nicolas Cage is a horrible actor in that movie, not even Ed Harris or Sean Connery could save it.

 

[jfed85]

wanna talk about a movie with some rediculously fake gun scenes? How about "Hot Shots" haha, couldnt resist.

 

[Scout]

I know what you mean. I'm a car guy. The first Fast & Furious movie was so fake it wasn't even funny. The following ones tried to be less "technical" and more entertaining. Which they were.

Ever watch "My Cousin Vinnie"? The car related stuff is pretty accurate.