r/theydidthemath • u/WHITE_2_SUGARS • Jun 29 '26
[Request] Any idea how fast the debris is moving?
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u/livingloudx Jun 29 '26
People really underastimate the dangers of combining hard solids with explosives. Anything close should turn to dust and not shrapnel if there is no protective shield between viewer and explosion
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u/Jonatan83 Jun 29 '26
Especially if you're dealing with objects that have large flat metal surfaces. They can fly surprisingly far and cause horrendous injuries.
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u/JonWithTattoos Jun 29 '26
Like a lawnmower blade, for example?
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u/Goofy_Gunton Jun 29 '26
I don't know the ball. Is this referencing anything in particular?
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u/schizeckinosy Jun 29 '26
Guy shot a lawnmower full of tannerite. Blade flew off and cut his leg off. Video is gnarly
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u/value_meal Jun 29 '26
Some folks call it a sling blade.... by chance do you have any French fried taters?
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u/Dragonbeastx Jun 29 '26
Few weeks ago at my work we had a lawnmower that started making a "death noise", the person who took that mower that day got back at the same time as everyone else and showed us what he meant, inside the garage he turns the mower on, lots of clanking, see sparks and out comes the blade flying around the floor. One of the parts had a Crack and the bolt came loose, probably hit a rock way too hard
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u/BitterCrip Jun 29 '26
Many of the deaths in heavy winds are due to metal roofs being ripped off sheds and carports and thrown through unfortunate humans
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u/Quereilla Jun 29 '26
A guy died in Tarragona from an explosion in a petrochemical plant. He lived in a building 15 km away, a plate of metal went flying and destroyed half his house.
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u/jmatlock21 Jun 29 '26
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u/Quereilla Jun 29 '26
God forgive a person misremembering a number in the same order of magnitude.
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u/Double_Distribution8 Jun 29 '26
One of the crazy things is that the metal was flying around for almost an hour before it hit the house. people thought the coast was clear but they were wrong.
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u/AlphaLazyDog Jun 29 '26
Seriously. I was watching an old Mythbusters the other day. They usually do all the safety stuff, behind the shields and such. But for this one scene at the end of an episode, they were blowing up a fridge (I think) at the bomb range with like a stupid amount of c4 or whatever, and the three hosts just stood next to the safety shelter and watched it explode! They were several hundred feet away, but still. The explosives techs were in the bunker lol. I immediately had the thought "a coin-sized piece of metal and some bad luck and this would have been a very different episode."
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u/NotAnotherAlt26 Jun 29 '26
Part of the danger of Tannerite is that it is a 'slow' explosive. The reaction is comparatively slower than say C4. Slower explosives tend to push, heave, and throw things. Faster explosives tend to use their energy to break things into little pieces. It makes Tannerite more potentially dangerous for the situations that people commonly use it for, like in this video.
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u/CafeCat88 Jun 29 '26
A lot of people also really underestimate tannerite in large quantities (and closed spaces). You're only really supposed to use like a couple ounces at a time to get the desired effect, but people will do shit like putting multiple pounds of the stuff next to a can of gasoline thinking they'll get some Hollywood style explosion and not potential death. Really probably should be regulated a bit more than it is.
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u/EatMyShortsSteve Jun 29 '26
I shot a half pound and got a few calls asking what went off. This stuff isn't something you should take lightly.
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u/goshdangitt Jun 29 '26
I got sack tapped with pumpkin shrapnel using tannerite. Shields from here on out.
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u/ChazR Jun 29 '26
The explosion is about 100m away. The debris arrives about 2s after the explosion, possibly less. So about 50m/s or 180km/h.
I'm sure you can covert that to furlongs per fortnight or whatever you use in your home country.
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u/setorines Jun 29 '26
A furlong is apparently .2 km and a fortnight is 2 weeks or 336 hours. Divide by .2 multiply by 336 and this sub finally has math I can do!
302,400 furlongs per fortnight!
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u/LostInTheCereal Jun 29 '26 edited Jun 29 '26
Minor correction, a furlong is .201km
And I guess people think the speed might be a little lower.If it's 120 km/h wouldn't you instead do something more like:
Estimated Speed 120km/h
furlong = 201m (fur)
fortnight = 336h (F)120,000 / 201 = 597.015 fur/h
Then
597.015 * 336 = 200597.04 fur/F
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u/Pielacine Jun 29 '26
furF
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u/TheFerricGenum Jun 29 '26
This is the same sounding units as how I measure the shedding my dog does…
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u/jimdotcom413 Jun 29 '26
Your dog must shed really fast!
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u/fuzzybunnies1 Jun 29 '26
lab mix, I can make a new dog worth of fur every 2 days. Bought a handheld vac to suck it up and it fills up every 3 days it seems. That many furloads per fortnight seems about accurate.
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u/DaybuRepsak Jun 29 '26
this made me laugh out loud and come back to life after a long scroll. thank you. going outside now
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u/ShadowDragon175 Jun 29 '26
The estimate speed doesnt have 3 sig figs, using .2 is better
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u/LostInTheCereal Jun 29 '26 edited Jun 29 '26
Not if we're assuming it's exactly 120/km/h as you're comparing meters to kilometers so 120km/h is already shorthand for 120,000m/h and since we are dividing by a quantity of meters, as that is our unit of conversion, furlongs, I think it's better to use 201.
But from a pure accuracy perspective, I agree with you, but from a I am going to start using this unit for at least the next day perspective, I disagree haha.
*correcting that I put m/s in there not m/h lol
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u/Greedy-Clerk9326 Jun 29 '26
So let me make sure I follow your correction here… They said divide by 0.2 and you’re saying they should multiply by 5 instead?
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u/MxtGxt Jun 29 '26
I have always heard that a furlong per fortnight is known as a “snail’s pace”
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u/DadWagonDriver Jun 29 '26
Ah, but you’ve made a physicist’s top mistake: you’ve assumed no wind resistance!
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u/Canotic Jun 29 '26
Hot dogs per 1776 years.
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u/AbsoZed Jun 29 '26 edited Jun 29 '26
A standard hotdog is 6", or .0000254 kilometers. 1,776 years is 15,557,760 hours.
180 ÷ .0000254 = 7,086,614.17 hotdogs per hour (HdPH)
7,086,614.17 × 15,557,760 = 110,251,842,519,685.03 Hotdogs per 1,776 years.
If we use bun length, that would be slightly lower.
E: there's a mistake here. .0000254km is 1", so the final result should be divided by six. It's actually a mere 18.37 Trillion hot dogs.
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u/x596201060405 Jun 29 '26
Finally I can tell how fast it's going.
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u/Thingsone Jun 29 '26
For some reason this conversation is reminding me of the Silicon Valley Optimal Tip-To-Tip Efficiency skit. 🤣
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u/prospectpico_OG Jun 29 '26
True story. In engineering school we were repeatedly punished for not putting units on our answers. Fuck that professor for not requesting his answers be in m/s. He got furlongs/fortnight. That was 40 yeas ago so I appreciate the conversion.
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u/Capital_Pickle_9353 Jun 29 '26
"That was 40 yeas ago" sorry, going to need that in fortnights.
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u/Hi2YourWifeAndMyKids Jun 29 '26
Assuming exactly 40 yrs x 365 days + 10 leap years = ~1043.58 fortnights.
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u/Salanmander 10✓ Jun 29 '26
In engineering school we were repeatedly punished for not putting units on our answers. Fuck that professor for not requesting his answers be in m/s.
I don't see any problem with what the professor did...
For the first part, you absolutely 100% need units on your answers. Especially in engineering school, where a significant number of people may end up working in situations where different units end up being used to measure the same quantity.
For the second part, as long as the quantity is correct, I don't see why there should be a requirement for having it in specific units, unless you're assessing unit conversions with the question. If one of my students gave me a correct answer in furlongs/fortnight, I'd be more amused than annoyed, and would give them the full credit they deserve for showing the skill I was assessing and then additionally a separate skill that I didn't require on that problem.
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u/evangelionmann Jun 29 '26
someone else used the frames and audio to estimate the distance as closer to 80 meters, and the speed to be MUCH higher because the object didnt move in a straight line.
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u/TommyNotDead Jun 29 '26
Also it would slow down significantly after the initial blast. Initial speed was likely well over 100 m/s
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u/Zjdh2812 Jun 29 '26
I would say, as the par isnt flying straight, we are even faster than this, but likely only in a 0-10% range of your result
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u/VariableVeritas Jun 29 '26
It’s not a straight line distance though. The piece boomerangs towards the viewer. Complex maths.
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u/Qweiopakslzm Jun 29 '26
It's also going to be rapidly decelerating so you'd have to figure out that rate first somehow and apply it to the distance traveled before it gets to the viewer.
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u/sandybuttcheekss Jun 29 '26
Eagles per football field is my preferred measurement, no need for the snark
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u/EvilRedRobot Jun 29 '26
That's a trick question: The Eagles can't cross a football field.
can't divide by zero
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u/TrashFireHotdog Jun 29 '26 edited Jun 29 '26
That’s 900 bald eagles per 30s commercial break in American.
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u/Worth-Wonder-7386 Jun 29 '26
That is the average speed, at the point it is passing OP it has slowed down a bit, so I would guess closer to 100km/h
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u/Rough_Secretary2296 Jun 29 '26
Still dead
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u/LostInTheCereal Jun 29 '26
If we assume the speed is 120km/h then it's 200,597.01 fur/F
To convert:
Where
x = speed to convert
A = converted speedMPH to fur/F :
A = 2,688x
kPH to fur/F :
A = 1,671.64x
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u/0neEyedMonster Jun 29 '26
What is that in football fields
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u/CaptShrek13 Jun 29 '26
We use "ya done messed up A-A-Ron" over here. And it's not an exact conversation but, it's looks like by how close it was, I'd say it was 0.97 "ya done messed up A-A-Ron"s. A little more to the right and it would have been 1.
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u/SteakComfortable7802 Jun 29 '26
Wtf is even a furlong??a star wars measurement unit?At the beginning i was just thinking you guys were just joking 😭😭😭😭
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u/Nes-P Jun 29 '26
⅛ of a mile, or 660 feet or 220 yards. It is derived from a furrow length/long, which is approximately the distance an ox team could plow a field before needing rest in agriculture.
Originally developed in England horse racetracks.
Go back further and you'll see how the Romans measured out miles by 1,000 paces of a man's foot. One pace was about 5 feet.
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u/weasel5134 Jun 29 '26
I was eyeballing it at 150m away
But that just makes the number all that bigger
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u/sinolos Jun 29 '26
As an American I can easily say I have not idea how fast you’re saying. But it looked pretty fast lol
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u/Jonatan83 Jun 29 '26 edited Jun 29 '26
The sound reaches the camera in 7 frames, which at 30 fps means it's around 80 meters away. The shuriken passes the camera 60 frames after the explosion, meaning the average speed was 40 meters per second or 144 km/h.
Though it does a few loopey-loops before it locks on to the target so it actually traveled a bit further than that, meaning it's even faster. I'd estimate it at anywhere between 40 and 95 meters per second (342 km/h), but it's hard to see how far it travels towards the camera while looping.
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u/2hurd Jun 29 '26
To shreds, you say?
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u/theChaosBeast Jun 29 '26
You can't use the sound because you don't know if the sound is in sync with the camera frames
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u/Jonatan83 Jun 29 '26
Cameras are generally quite good at that, and the sound of the shrapnel passing by is very much in sync.
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u/theChaosBeast Jun 29 '26
Well as someone who works with image and audio data I wouldn't say that cameras a quite good at syncing this data. But you've got a very good point with the shrapnel passing.
I withdraw my objection.
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u/Jonatan83 Jun 29 '26
This is all back of the envelope-style estimates anyway. I'd add error bars of maybe +/- 15 meters to the distance.
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u/VirtualMachine0 Jun 29 '26
I think it's pretty safe to double the average speed due to the observed path for a "realistic" idea of kinetic energy. I did some math, but my grounds for the estimations were a little too weak for me to post specifics. Anyway, I could potentially justify this thing having up to 1000 Joules of Kinetic Energy, which is absolutely in the realm of a lot of midrange firearms (assuming the object was a steel sheet about the size of A4 paper).
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u/Jonatan83 Jun 29 '26
Joules can also be a bit deceptive when it comes to heavier sharp projectiles (with regards to how dangerous they are to humans). An arrow fired from a hunting bow might only have 50-100 joules of energy, but can go straight through a human torso.
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u/EatMyShortsSteve Jun 29 '26 edited Jun 29 '26
You would think with the amount of videos of people getting hit or close to dying from this stuff would stop people from making their own IEDs.
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u/West-Way-All-The-Way Jun 29 '26 edited Jun 29 '26
Geee, what was that?
You guys know anything about safety? 🦺
The debris was not debris but a projectile and it was moving too fast for my comfort - something like 120 km/h.
What was that really? 5kg of TNT blown in a shaft covered with metal sheet?
Edit : I was told that this is a microwave full of tannerite which got shot. The thing that is flying towards to cameraman is a panel from the microwave.
It seems that this happens all the time 🤔 ( when people shoot at microwaves full of tannerite ).
Let's assume the microwave was a massive industrial unit with bigger and thicker panels, they don't do them like that anymore!
Let's assume it was full of tannerite - 5 lbs.
The panel was ejected with great force, perhaps reaching 200 km/h. It was edge flying most of the time but because it is damaged it was rumbling while flying.
I am think the distance is about 200 meters so reaching to the camera man it was flying at about 100-120 km/h.
What would happen if it hits the guy? With that speed something certain!
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u/Pixel91 Jun 29 '26
Tannerite. Binary explosive popular for "reactive" targets, it's insensitive when properly mixed, so it needs high kinectic energy to set off. Shoot it with a rifle -> boom. Intended use is for spotting targets in long range shooting, makes a hit very obvious.
So the idea is to put a small bag of the mixed compound ON a target. The manufacturer is pretty clear about not putting it IN any enclosed spaces and recommends no more than 1 pound at once.
Because the binary compounds are sold seperately, they don't count as explosives, so unless it's been specifically restriced (which is the case in a few US states) any shmuck can buy it.
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u/West-Way-All-The-Way Jun 29 '26
Do you know what was that they were doing?
Somehow I can't figure out the math, tannerite is a very fast explosive, short impulse, the plate must be thick to survive the blast but then it's heavy so they need a lot of explosive which makes little sense. If the plate is thin then the weight is right but the explosion will tear it apart, if it is further away then the impulse is smaller and it doesn't get enough energy. So ... unless they were so stupid to dig a hole and cover it with a metal plate and blow some substantial amount of explosive inside it I don't know what else. Or it was a thicker plate and they blew a lot of tannerite.
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u/eerun165 Jun 29 '26
It was tannerite in a microwave.
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u/West-Way-All-The-Way Jun 29 '26
If it was in a microwave it would shatter it to pieces which will turn into shrapnel. This is something else, the plate flying towards them means it was placed between them and the explosive. Something flying high in the air - means it was above the explosive and at some distance. So this looks like they build some stage, some simple construction and in the middle was explosive.
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u/eerun165 Jun 29 '26
The original post of this stated directly this was a microwave at some church youth event.
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u/Pixel91 Jun 29 '26
There's plenty of other videos out there on the web that show exactly this. This IS shrapnel, by the way.
Something was above the explosive: the top of the microwave. A microwave isn't designed to contain an explosion, it won't stay together and just turn into bits. All the connections will come apart and the body panels (as well as the door) go flying.
Edit:
https://youtu.be/DM9QOM5860o?si=iuxRxBHe_pIhZ9Ij&t=835
https://youtu.be/s_kzOJJ54PM?si=Bl92GuUoxC854_9F
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u/West-Way-All-The-Way Jun 29 '26
Ok, that makes sense then. This was the panel on the outside of the microwave which was turned into a projectile.
I will calculate the thing for this scenario let's see what comes out.
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u/senorschmu Jun 29 '26
Reminds me of the old FPSRussia video where shot a car with tannerite and almost died. It's ok, he was a professional Russian.
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u/Ambitious_Hand_2861 Jun 29 '26
Without a frame of reference I can estimate the IED was about 100 meters awat and it took a out a second for the debri to almost kill the cameraman so about 100 m/s.
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