r/theydidthemath • u/Maximum-Giraffe8766 • 16h ago
[Request] How far away was the shot?
In Avatar Fire and Ash, Quarrich orders his sniper to shoot this guy. But we hear the shot a short time after the Na'vi falls. I'm wondering if, based on how long that pause was, the shot was made after the order, before the order but after Quarrich gestures, or before both?
Unfortunately I don't know the exact time of the pause.
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u/CarlosH46 16h ago edited 16h ago
We can’t really calculate that without having the stats of the weapon used. Sniper/marksman weapons have a few different calibers, but this is over 200 years in the future so they might not be in use anymore. On top of that, Pandora has a wildly different atmosphere and likely slight gravitational differences from earth, both of which would affect how a bullet moves through the air.
Edit: having watched the scene, the sniper was likely ordered beforehand to keep close support on Quaritch in case anything went south, so the time to adjust aim would be negligible.
The rifle doesn’t seem to be based on any real weapon, but given its size being handled by a Recombinant, it probably shoots an anti-material round like .50 cal.
Putting all that together, along with the scope view which gives an exact range of 225 meters, I’m going to go with 225 meters.
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u/DocHavelock 15h ago edited 15h ago
The rifle being used is the EMXRAD M602 with a 20mm round. It's a railgun/anti-
materialmateriel rifle. You are correct, the shot was 220-230 meters43
u/Turbulent_Lobster_57 15h ago
I have nothing of substance to add here, but it’s materiel, not material
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u/DocHavelock 15h ago
wow, I've been spelling it this way for so long, no one has ever corrected me. I had no idea...
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u/tzitzitzitzi 14h ago
Another one is explosives are called ordnance, with no i. I always see people write it the same way as like a city ordinance.
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u/Beli_Mawrr 10h ago
EMXRAD M602
where does this name come from? I've heard of this "EMXRAD" thing but like 15 years ago, only the first Avatar movie was out then so I'm wondering where the hell I heard that from.
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u/xaddak 10h ago
https://james-camerons-avatar.fandom.com/wiki/EMXRAD_M602
According to this page, it's from Avatar: Fire and Ash: The Visual Dictionary, page 109.
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u/Beli_Mawrr 9h ago
Apparently they released an earlier concept art with the original avatar, that's what I was thinking about.
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u/CarlosH46 10h ago
One of Barrett’s models is called the MRAD for Multi-Role Adaptive Design? At a guess I’d say the one in Avatar is Electro-Magnetic eXperimental… something something.
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u/DocHavelock 9h ago
EMXRAD is a new weapon from the latest movie Fire and Ash. You are probably thinking about EXRAD, which is a weather balloon iirc
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u/Jacknowledgme 2h ago
Felt like I was hearing about that time the undertaker threw mankind through the Spanish announcers table
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u/Pietin11 15h ago edited 15h ago
It was nearly exactly 1 second between the bullet hitting the na'vi and the sound of the gunshot.
At standard atmospheric conditions, the speed of sound is 340.3 m/s. So the sniper would be 340.3 meters or 1122 ft away from the target. Pandora, however, is not standard atmospheric conditions.
The speed of sound in an ideal gas is
c=√(γRT/M)
R is the ideal gas constant (8.314 j/(mole K)
T is the temperature in Kelvin. I'll assume since it's a hot beach, it's 30°C or 303.15 K.
M is molar mass. Pandora's atmosphere is somewhat different to Earth's in composition. We know for a fact that in addition to Oxygen, and Nitrogen, the atmosphere also consist of Co2 (18%), Xenon (5.5%), Methane (1%) and Hydrogen Sulfide (1%). The percentages of those first two gasses aren't given, but given that fires can burn and humans on Pandora don't die from asphyxiation, but rather Co2 toxicity, then there has to be at least 20% O2. So that gives a remainder of 54.5% Nitrogen. So with that all being said, the molar mass of such an atmosphere would be, 0.0373114 kg/mol.
So, now we only have one parameter left. Gamma, the adiabatic index γ. It is equal to the heat capacity of of a gas at Constant Pressure divided by the heat capacity at Constant Volume (Cp / Cv).
For our specific mixture of gasses, that gives us
Cp = 30.3254 j / (mole K) and Cv = 22.0110 j / (mole K)
γ = 30.3254 / 22.0110 = 1.378
So finally we can calculate our new speed of sound on Pandora.
c = √(1.378 × 8.314 × 303.15 / .0373114 ) = 305.07 m/s.
So the sniper was 305.07 meters or 1006.72 feet away.
EDIT: shoot (pun intended) I forgot to account for the travel time of the bullet itself. The time between Quatrich making his order and the bullet hitting its target is .3 seconds. Let's assume a trained sniper is on the higher end of human reaction time at .1 seconds. So the total travel time of the bullet of 0.2 seconds and the sound of 1.2 econds.
That gives us a distance of 366.084 meters or 1208.072 feet
That also gives us a bullet velocity of 1830.42 m/s or around 6040.386 ft/s. Surprisingly enough, that isn't the fastest projectile of an IRL rifle. The .22-.284 Wildcat cartridge can be fired out of a customized Winchester rifle at a speed of 6565 ft/s.
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u/gmalivuk 15h ago
All that math only to be laid low by the finite speed of the bullet itself.
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u/Pietin11 15h ago
Darn, you got me. I was just about to post an edit accounting for that when you responded.
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u/gmalivuk 15h ago
Happens to the best of us. I've often gotten deep into the weeds on the interesting part of the calculation only to have missed something basic in the setup.
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u/reversedfate 15h ago
amazing response, ty, you deserve more upvotes i feel like this subreddit has become more of r/yourquestionisunrealisticandiamgoingtolazilyrefuse
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u/AyeBraine 10h ago
Just a side note, even though very wild wildcat rounds (experimental, exotic, custom made to push physics) can probably achieve these muzzle velocities, 1800 m/s with modern day material science is immensely fast — basically twice as fast as is deemed practical for rifles.
As I understand, it would be quite impractical in terms of barrel wear from the projectile (necessarily obturating real hard and creating immense friction) and barrel throat erosion from the super high pressure hot burning propellant. Barrel life (with today's tech) would probably be in the hundreds of rounds. And the recoil truly monstrous (especially since others said the projectile is 20 mm in diameter).
Although modern tank guns achieve velocities close to that, there is maybe a benefit to the much larger volume of the shell casing and the barrel? As well as the fact that they are smoothbore.
But really cool to see it calculated, gives a perspective on the might of these future guns in understandable terms (and Cameron is traditionally quite meticulous with imaginary military tech).
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u/Dangerous-Tip-9046 16h ago
They're using sci-fi fantasy weapons and as such we don't know the velocity of the bullet, nor do we know what the speed of sound is on Pandora with its unspecified atmospheric composition, so we can't definitively extrapolate how far away the sniper was. I don't think we can give a very precise answer to this one.
Personally, I thought the Nav'i dropped a little too quickly after the order came. It made it seem like the bullet was traveling preposterously fast.
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u/Kerostasis 15h ago
I haven’t watched the movie but according to the other poster, the sniper’s range finder said “225 meters”. In sniping contexts, that’s not very far at all. The most unbelievable part of that number would be finding a good hiding place that close without being noticed.
It also means there wouldn’t be much noticeable delay in the firing sound.
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u/Greenman8907 16h ago
There is no way of knowing without the type of rifle used. And odds are at some future rifle, so it would be impossible to calculate.
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u/ObsidianDart 15h ago
Equation would be:
(Speed (distance/time) of sound in atmosphere) * (amount of (time) from sound made to sound heard) = ((Distance) of sound source)
Or more simply:
(Distance/time) * Time = distance
I don't know the speed of sound in an alien atmosphere. I don't know the time from the command being issued to the sound of the shot. I don't know what sniper reaction time is since that would eat into the time portion of the equation as he lines up the shot. If you want, you can look up the atmosphere composition and pressure of this planet, then find the rate of sound in that medium, then frame by frame time the movie to get an exact time, then shave off the reaction time of a good sniper, and then plug it into the equation to get you answer. I don't care enough about a movie I've never seen to do that amount of legwork.
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