221 réponses à ce sujet

[Lycans Bane]

Obviously some don't like the use of layman's. With the crossbow scene there are several factors contributing to the target landing on his backside. 1. The target is running, an action that generally reduces balance. 2. The force applied to the target by the bolt is transferred in such a that reduced momentum of target around point of contact. 3. While part of the target's momentum diminishes the other stays relatively the same. 4. The range reduces time for the bolt to deccelerate. The reduced balance obviously makes it easier to knock the target down. And when the factors are looked at together there is a slight pivot effect on the target knocking him down.

[Lotion Soronarr]

Actually wrong...since the target is running towards Varric, it has momentum going in the opposite direction of the bolt. And 100kg of man running towards you mean a lot of momentum.



Think of it as a large truck colliding with a small car..The truck isn't the one to be pushed backwards.

[Sir JK]

He's right Lotion (as are you incidentally).



What basically happens is that the bolt (which is fired from a warcrossbow which can have a drawweight of between 200 and 1200 pounds depending on era) causes the area it hits to decelerate and stop. However... nothing else stops. So the legs, arms, head, shoulders have momentum forward but the torso have no momentum forward anymore. The legs, being the largest centre of mass with a velocity, will then shoot forward but the torso won't follow (arms are also shooting forward). Causing the same phenomenom as if one slipped on a sheet of ice while running... Which visually looks like one is indeed flying backwards (but one is still going forward... and then down)

[J-PV]

Mike Laidlaw wrote...
... Generally speaking, you can knock foes around about as much as you could in Origins. Maybe a bit more...well...depending on how you build your character, probably a LOT more. ...

And, it's a game so a little overdoing the "knock around" effect is quite all right.

[Lotion Soronarr]

maybe if we were talking about blunt impact, but crossbows pierce. The momentum transfer will not be sufficient to stop the are that is hit.

[Sir JK]

Lotion Soronnar wrote...

maybe if we were talking about blunt impact, but crossbows pierce. The momentum transfer will not be sufficient to stop the are that is hit.

Crossbow bolts, like arrows are designed to pierce their way into the target, but they're rather inefficient at maintaining the momentum (mostly because of shattering in the target) and thus mos often end up stuck. Unlike bullets who simply pass straight through their target. Mind... the vast amount of momentum is lost in flight.

You're right that a bolt (or arrow) is unlikely to achieve it at long range, or even medium range. At point blank range however the loss of momentum is negligible (if we don't count the momentum lost to the crossbow itself) so there it could slow down the area it hits enough to cause the effect (it doesn't need to stop the target area completely).

Naturally, if the bolt would hit centre of mass or a point of balance then you're right. It couldn't move the target. But if it doesn't... then it might.

[EmperorSahlertz]

That would depend on the kind of bolt fired from the crossbow. If it is small and light it would pass right through the target. If it is broad and heavy it could possibly happen as Sir JK described.

[Tiax Rules All]

You all sound pretty silly argueing this the way you are but I'm about to join you. Lotion is more correct. What would essentially happen is the guy would get shot and he would not get blown backwards, nor would he do that wierd thing Sir jk suggested. In hollywood yes.. in DA2 it looks like it but in reality it would peirce, he would fall, like a small to medium caliber bullet.



of course thud, yelp, fall would be dull compared to gore explosion and dramatic blowback so there it is.

[Lotion Soronarr]

Though popularized in television and movies, and commonly referred to
as "true stopping power" by novice or uneducated proponents of large
powerful calibers such as .44 Magnum, the effect of knockback from a handgun and indeed most personal weapons is largely a myth. The momentum of the so-called "manstopper" .45 ACP bullet is approximately that of a 1 pound (0.45 kg) mass dropped from a height of 11.4 feet (3.5 m).[9][note 1]
Such a force is simply incapable of arresting a running target's
forward momentum. In addition, bullets are designed to penetrate instead
of strike a blunt force blow, because, in penetrating, more severe
tissue damage is done. A bullet with sufficient energy to knock down an
assailant, such as a high-speed rifle bullet, would be more likely to
instead pass straight through, while not transferring the full energy
(in fact only a very small percentage of the full energy) of the bullet
to the victim.
The "knockback" effect is however commonly "seen" in real-life
shootings, and can be explained by physiological and psychological
means. Humans encountering a physical hit, be it a punch or a bullet,
are conditioned to absorb the blow by moving in the same direction as
the force. The physical effect against a non-penetrating weapon is to
reduce the force felt by the blow, and in addition, retreating from an
attack increases the distance such an attack must cover, which in the
case of non-projectile weapons such as fists or a knife, places the
target out of range of further attack. In addition, there is a
theoretical sociological explanation, that in modern civilization, with
far greater separation by most individuals from violence, hunting, and
combat, normal individuals may simply recoil, buckle, or fall backward
when hit by a bullet, even when in pure physiological terms they are
perfectly capable of continuing to charge.
Although knockback is not possible with a handgun bullet, it can be
an actual effect occurring in reaction to being hit by a massive slug,
such as a rubber bullet or sandbag fired from a shotgun.
The dynamics of a slug round are quite different than penetrating
bullets; the projectile is here designed not to penetrate but instead to
strike a hard, blunt force blow, and as the momentum carried by a
shotgun cartridge is greater than practically any production handgun
cartridge, the force imparted is comparable to a hard punch and is
capable, by physics, of affecting a person's forward motion. In any
case, due to conservation of momentum, the gun's recoil is always larger
than the bullet's knockback, as some momentum of the bullet is lost
during flight, and if the bullet penetrates through the target it will
not have imparted all its momentum into the target.

I rest my case

[upsettingshorts]

I applaud your taking a stand when it comes to technically unrealistic momentum physics in fiction. One down, eleven billion more examples to go.

[Sir JK]

Absolutely Lotion. A very well written analysis (and if you didn't write it: good find). It is certainly true in terms of guns.



However... bows and crossbows don't work entirely similar. For one... the recoil is actually aimed forward (so if you shoot a really powerful bow or crossbow... you won't be pushed back but dragged forward). Another is that they're based on tensile strength, just like springs, which imparts momentum differently (and less effectively). The third being that an arrow or bolt have a lot higher momentum due to simply having higher mass.



To clarify: No projectile that's not explosive or self propelled have the momentum necessary to push a human back.



But:

If a projectile hits in the right spot, they may cause a knock down (which may look, from certain perspectives like a knock back. But it is not). In the same vein, in unarmed throws you don't actually lift persons... just apply a small amount of force in the correct spots. This is the exact same thing, but with a projectile.

A crossbow bolt, hitting in the correct place (it's very unlikely shot) can cause what amounts to a series of destablisations and a very local deceleration that might cause someone to "slip" (which from the shooters perspective will look like pushing the target backwards... despite that it still moves forward).



It is not a knock back.

It is not the bolt moving anyone backwards

But it sure looks like it.

[ShrinkingFish]

Lotion Soronnar wrote...

Although knockback is not possible with a handgun bullet, it can be
an actual effect occurring in reaction to being hit by a massive slug,
such as a rubber bullet or sandbag fired from a shotgun.
The dynamics of a slug round are quite different than penetrating
bullets; the projectile is here designed not to penetrate but instead to
strike a hard, blunt force blow, and as the momentum carried by a
shotgun cartridge is greater than practically any production handgun
cartridge, the force imparted is comparable to a hard punch and is
capable, by physics, of affecting a person's forward motion. In any
case, due to conservation of momentum, the gun's recoil is always larger
than the bullet's knockback, as some momentum of the bullet is lost
during flight, and if the bullet penetrates through the target it will
not have imparted all its momentum into the target.

I rest my case

Your science is very impressive.

However. I have seen a man shot at point blank range with a shotgun. And it did indeed lift him off his feet and throw him to the ground.

Granted. The trailer may have exagerrated it a bit. But it didn't just pull the event out of its metaphorical ass.

I think people are making too much of what happened in that half a second clip. I mean... to my eyes, the guy didn't fly backwards. He just lost forward momentum, his arms and legs flew out, and then it cut to the next scene. We didn't even see him hit the ground. Not nearly that big a deal.

Modifié par ShrinkingFish, 03 novembre 2010 - 10:31 .

[upsettingshorts]

I'd like to be pedantic too and point out the term point blank is frequently misused.



Point blank simply means the target is close enough that you are not raising the barrel to add arc to a shot and thus extend the range of the projectile.

[ShrinkingFish]

Upsettingshorts wrote...

I'd like to be pedantic too and point out the term point blank is frequently misused.

Point blank simply means the target is close enough that you are not raising the barrel to add arc to a shot and thus extend the range of the projectile.

And Varric's target was definitely at point blank range. Well within it if the looks aren't decieving.

[upsettingshorts]

ShrinkingFish wrote...
And Varric's target was definitely at point blank range. Well within it if the looks aren't decieving.

Oh indeed he was.

[ShrinkingFish]

Upsettingshorts wrote...

ShrinkingFish wrote...
And Varric's target was definitely at point blank range. Well within it if the looks aren't decieving.

Oh indeed he was.

Just rewatched it for fun...

Yeah. He definitely was. Haha. Poor guy was within point blank range of a stone's throw.

[ShrinkingFish]

But while we're talking about shotguns (one of my favorite subjects) let me share this with you.



It is out dated now, so I'm sure many of you have already seen this... but its still a favorite of mine.



http://world.guns.ru...tgun/sh10-e.htm



The Jackhammer Shotgun. MmmMmmm, sexy boomstick.

[upsettingshorts]

I'm a fan of golf with a shotgun! (sporting clays)

[Lotion Soronarr]

I applaud your taking a stand when it comes to technically unrealistic
momentum physics in fiction. One down, eleven billion more examples to
go.

Truth be told, that had  little to do with the game itself. I just hate small,, but cruical mistakes like that, and feel the need to correct people when they think X is real, when it's actually just a myth.

ShrinkingFish wrote...

However. I have seen a man shot at point blank range with a shotgun. And it did indeed lift him off his feet and throw him to the ground.

Was that man standing still or running forward? Leaning any particular way?

Mind you, the quoted paragrap was from wikipedia, on the very subject of weapon knockback.

[tmp7704]

Lotion Soronnar wrote...

Although knockback is not possible with a handgun bullet, it can be
an actual effect occurring in reaction to being hit by a massive slug,
such as a rubber bullet or sandbag fired from a shotgun.

I rest my case

It'd actually seem the source you cite disagrees with you -- crossbow bolt is after all quite bigger than bullet from a handgun, and as such may be able to do what a shotgun slug is said to be capable of? (depending how well it can penetrate the target, granted)

Modifié par tmp7704, 03 novembre 2010 - 03:51 .

[Lotion Soronarr]

Crossbow bolts are also designed to penetrate and don't have the power of a rubber shotgun bullet, which is specificly designed for that effect.



It also depends on the mass, speed and center of mass of the target.

[EmperorSahlertz]

A crossbow bolt was designed to penetrate yes, but it weighs a lot more than a handgun bullet. The crossbow bolt won't pass straight through its target (like bullets sometimes do). By the end of the day saying that kockback isn't realistic is untrue. It all comes down to force of the projectile. Obviously Varic's Crossbow got a lot of power (and it was close range).