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It turns out this is pretty easy if you drill a hole in the piece of wood first |
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The thing is, a tornado will not drive a straw through a
piece of wood. |
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Consider for a moment. Suppose the straw is moving at
200mph, and the plank is standing still. The straw hits the
wood at 200mph. |
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Meanwhile, in a well-sheltered basement, a man has
another plank and another straw. He balances the straw on
end, and hits it with the plank. The plank is moving at
200mph as it hits the straw. |
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Now, what will happen in the second situation? And
therefore what will happen in the first situation? |
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I suspect that this myth arose because, if there is any pre-
existing hole in a plank that's in a tornado, there's an
excellent chance that stuff will get blown through the hole
until something sticks there. I'd also be very suspicious of a
piece of straw which was sticking out of a plank and had
miraculously not been snapped off by all the tornading. |
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I'm reminded here of the use of samurai swords in some genres of cinema. The way they are used suggests that as you make the sword of increasingly harder steel, and make the edge increasingly sharp, the effort needed to cut through things diminishes to nearly zero. I suppose this only works up to a point; No matter how impressive a sword you have, cutting through a material (the neck of someone who has dishonoured you, an opponent's sword, etc.) still has to overcome the chemical binding energy of the material. |
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Ahem... "A method of estimating speed is to use
Doppler on Wheels to sense the wind speeds remotely,
[5] and, using this method, the figure of 486 km/h
(302 mph; 135 m/s) during the 1999 Bridge Creek–
Moore tornado in Oklahoma on 3 May 1999". |
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Later edit - ignore my ego, I try to. |
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If wind blown straw was capable of such ballistic
superpower you'd see whole pastures full of dead animals. |
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//302 mph// So, if you hit a piece of straw with a plank at
302 mph (or even, say, 303 mph), the straw will be OK? |
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Or perhaps the military have been missing a trick, and
should be developing low-velocity straw bullets. |
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//developing low-velocity straw bullets. |
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Well, there was the film Straw Dogs (not my cup of
tea) and The Dogs of War - which cleverly edited out
the hypersonic bits of straw. |
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Does the environment of 300 odd mph of laminar hurricane air around the straw count? |
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Never heard of straw through wood but wood through concrete during tornadoes and hurricanes is well documented. |
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//Consider for a moment. Suppose the straw is moving at
200mph, and the plank is standing still. The straw hits the
wood at 200mph.// |
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You're forgetting about the headless nail super-glued to the
front end of the straw [Max]. |
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Is it possible that a straw could end up traveling faster
than the maximum measured wind speed? Assuming that
max wind speed was measured by a cup anemometer,
that will provide some averaging, and those are normally
situated away from other objects. It seems like the wind
wiping around obstructions could generate swirling winds
with local velocities that were somewhat higher. |
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I also just watched a YouTube video of a Nerf dart being
fired through a 3/4 inch plank. See link. |
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So I won't say that this is definitely possible, but I'm don't
think Mythbusters busted the myth completely. |
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Nope. No hits for straw through wood. Maybe that's why the last little piggy built from other materials. |
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//Meanwhile, in a well-sheltered basement, a man has another
plank and another straw.// |
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Ah, those long winter evenings. |
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//Is it possible that a straw could end up traveling faster than
the maximum measured wind speed?// |
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Even if it were, it makes no difference. A piece of straw will
not survive being hit with a fast-moving plank, and the same
situation prevails if it's the straw that's moving. |
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Ok, last try....two contra-rotating tornadoes, one
contains a straw, the other one has a plank. |
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Or, maybe I'm just grasping at straws? |
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Anybody know what speed the straw would have to be
traveling at to punch a hole in the board? I'm sure there's
some kind of egghead calculation of relative density of the
two materials with speed factored in or something. |
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Does a rain drop puncture a ten food titanium wall when it
gets close to the speed of light for instance or does all that
speed get transformed into another form of energy turning
the drop into plasma or something? Does a straw puncture
the wood once it's going, say... 100,000 miles per hour in a
vacuum? |
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By the way, I didn't even go to high school and whatever I
know I learned on my own, mostly from books at the
library so please consider this before giving me an
intellectual wedgie. |
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//Anybody know what speed the straw would have to be
traveling at to punch a hole in the board?// |
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Well, if it were travelling at a few percent of the speed of
light, it would vaporise on impact and burn a hole (probably
a very, very big one) through the plank. |
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Seriously, [doc], see above. Ask yourself the reverse
question and see if it makes sense: how fast would a plank
have to be travelling such that, when it hits a stationary
piece of straw, the straw survives the impact? |
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Didn't say anything would survive the impact, I said would
the
two materials be traveling so fast relative to each other
that
a hole would be punched through the board by the
molecules
of the obviously vaporized straw. (I understand it doesn't
matter which one is moving, thought that went without
saying) |
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I'm uneducated, not stupid. |
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Anyone else wanna give it a shot? |
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//Anybody know what speed the straw would have to be
traveling at to punch a hole in the board? I'm sure there's
some kind of egghead calculation of relative density of
the two materials with speed factored in or something.// |
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Yes! Exactly that, it's origins are derived from the
Bernoulli equation. In its basic form P=L √μ. Or
penetration depth = Length of the penetrator * square
root of the ratio of the two densities. There's a lot of
refinement from experimental data, mostly about
material properties. I'll have a proper answer once I've
finished a rather weighty tome I've acquired about
terminal ballistics. |
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Surprisingly there's not a lot of good info on the
mechanical properties of straw, I found one reasonable
example <link>. I'll run a few calculations with a bit of
straw, some switchgrass - which is supposed to be denser
and an extreme example with a Lignum Vitae twig or
something. |
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If you Google "bullet mass", the first link says "A rifle can shoot a 4.20 g bullet at a speed of 965 m/s.". So a bullet's kinetic energy is about 1.9kJ. If the mass of a straw is about one tenth of the mass of a bullet it needs a speed of just over 3000 m/s to have the same kinetic energy. |
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OK ... it's not just about mass, or projectile shape, or projectile material. It's what clever people tend to call "very complicated" ... |
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There are a huge range of ammunition natures, for everything from .22 rimfire pistols to 15-inch naval rifles with a range or 30km. |
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In each case, the choice of projectile must take account of the specific characteristics of the target. |
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For example, you need a different type of AP (Armour Piercing) projectile depending on whether you're shooting at a tank, a concrete bunker, or a ship's deck. Something that's lethal to one might just graze another (altho a round from a 15" naval gun does tend to trump most defensive systems). |
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A straw is frangible, of low density, has a uniform mass distribution along its length, cannot be reliably spun around its primary axis to confer stability (thus ensuring an impact normal to the target's surface) and relies purely on the "kinetic penetrator" effect. |
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We will bet [MB]'s five dollars that a piece of straw, at less than luminary velocities, cannot reliably drill a hole in a plank. |
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// I'm uneducated, not stupid// I didn't say you were
stupid, [doc], or even uneducated. I thought you'd missed
the argument, that it's about relative velocities. |
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So, if you just want an impact big enough to destroy the
wood, and you don't care what happens to the straw, you
need the straw to have as much kinetic energy as the work
of fracture needed to break the wood in a plausible
pattern. And that is going to be a hugely huge speed. And,
as noted, the straw will come off even worse than the
wood. |
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OK, let's think laterally (lies down). I don't know much
about guns, but I think a smallish handgun bullet will barely
go through a one-inch plank - is that approximately true? I
mean, it's marginal? Let's assume so. So, a bullet
travelling at say 400m/s has just enough kinetic
energy to punch through the wood. Now suppose a piece of
straw weighs 1/20th as much as a bullet (a guess). To
deliver the same kinetic energy, it is going to have to be
travelling root-20 times faster, or about 1800m/s. |
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Given the collapsibility of straw, I suspect that only the first
few mm of straw deliver energy to penetrate the wood. So
you're really asking to deliver all the energy via that first
few mm of straw, weighing perhaps 1/200th as much as the
bullet. So now your up to a velocity of root-200 x 400m/s =
5600m/s, or roughly orbital speeds. |
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And thinking about orbital speeds is actually pretty useful.
Micro-debris such as paint-flakes can damage things like the
Shuttle's tiles, because they can impact at o.t.o. 7000m/s.
But they don't go straight through in the way a bullet would. |
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So, I think that sort of answers it. |
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I had to rush away while writing that last
annotation - what I meant to add was that a straw
doesn’t act like a bullet (in many ways) and that if
you wanted to test this you should start your
testing with the straw at 3000 m/s... |
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My bet's with that as well, but what about say, 25,000 MPH
in a vacuum? |
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What's the fastest non-sub atomic particle object we've
accelerated on Earth? (besides me rushing away from a
Halfbakery post about Donald Trump) In space it's 25,000
MPH or something. What about impacts on space stations
and satellites in orbit when they get hit with a grain of
sand or something? What's the closing velocity of those
impacts? When a grain of space sand hits the space station
does it just blast apart and leave a crack? As far as I know
the envelope of our various space stations and spacecraft
have never been penetrated. |
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By the time I wrote this, twenty posts had popped up
rendering everything I said unnecessary. |
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//rendering everything I said unnecessary.// (Boy did I set
myself up with that one.) |
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// I didn't say you were stupid, [doc], or even uneducated. // |
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That is, in the narrow sense, true. But why then have you given your brother $3 and a packet of bubble gum to follow him round with a Post-It note on which you have written "I'M DUMB, PLEASE KICK ME" to stick on his back as soon as an opportunity arises ? |
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// fastest non-sub atomic particle object we've accelerated on Earth? // |
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NASA has an impact simulator that launches metal spheres at stupid velocities to investigate cratering phenomena. That probably still holds the record. |
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On impact, the sphere instantly converts to plasma. |
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The hydrogen nucleii in fusion reactions attain very high velocities, but although they don't fall into your "sub-atomic" category (being merely atomic) we don't think they can be included in the contest. You're talking about something like a grain of sand, minimum. |
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You need to parameterise your question a little more closely. |
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I strongly resent the implication that I would ever give either
of my brothers $3. |
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I'm happy to wear the dunce cap in the room as long as the
head holding that cap leaves that room containing more
knowledge that it had upon entering. (And as long as I get
to keep the hat as a memento.) |
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So I need to know the exact closing velocity of a piece of
straw and a half inch piece of plywood that would result in
a hole in that plywood. It's obviously assumed that: |
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1- The straw would vaporize and... |
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2- This takes place in a vacuum. |
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Is this something where you could extrapolate by getting
the straw going fast enough in a real world experiment to
cause SOME damage to the board such that you would be
able to see that damage, perhaps with an electron
microscope then assume if X happened at Y speed, then
10,000 X would happen at 10,000 Y? Or... is there some
threshold that's met when
the straw becomes gas or even plasma that causes a
breaking point in the wood? |
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To a very rough approximation, you can estimate it as
follows. |
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(1) Assume that 10 grams of wood is to be vaporised. |
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(2) The energy needed to do so will be about a tenth (oto)
the energy you'd get from burning 10g of wood in air, which
is about 100kJ, so say 10kJ. |
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(3) Mass of straw is, say 10 gram (0.01kg). |
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(4) E=mvv/2, so v=root(2E/m), or 1400m/s. |
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(1) Assume that 21/64ths of an ounce of wood is to be
vaporised. |
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(2) The energy needed to do so will be about a tenth (oto)
the energy you'd get from burning 21/64ths oz of wood in
air,
which
is about 140,000 ft lb force, so say 14,000 ft lb force. |
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(3) Mass of straw is, say 21/64ths of an ounce (0.021lb) |
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(4) E=mvv/2, so v=root(2E/m), or 6.96 furlongs/s. That's
about 3100mph. |
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3,100 MPH? That's very doable in a lab using a rail gun,
supposedly those guys can get up to over 5k MPH. Just put
the straw in a sabot of of some kind that would be stripped
away and miss your piece of wood, or at least be steered
away from your straw target section, put everything into a
vacuum and let 'er rip. |
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I'll put that on my someday weekend project list. |
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I may have dropped a factor of 64 somewhere. |
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(...wonders if the MOD would be interested in some
50ft straws orbiting the planet? |
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Ideal for assassinating enemies who habitually live in
single-plank constructed buildings (bit of a niche
market I have to admit)) |
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Not sure about the Vulpine Dollar (in a Bear market), but a lot of the Coyote Dollar seems to go to the ACME corporation. A device that can fire bits of straw at 1.5 km/s sounds just the thing they'd want for the cover of their Spring '19 catalog. |
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// I strongly resent the implication that I would ever give either of my brothers $3 // |
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Sorry, Zimbabwian dollars - should have made that clear. |
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I own several Zimbabwean currency bills (at least I think
they're Zimbabwe - some African country at least), and the
smallest denomination is 1 billion. |
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//That's about 3100mph.// |
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That's doable with something like an SR-71. Instead of rods
from god, you could get away with chopsticks from
120,000ft |
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//Zimbabwean currency bills |
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...will be regarded as a hard currency after Br**it, so,
keep your put them in a safe place. |
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As [hippo] indicated and I have been thinking about this too much.
Is this a straw velocity? |
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The Number of hurricanes with correct wind conditions x fraction of flying straws, in a hurricane, in the 99 percentile of strength x (the fraction of trees in hurricane path with accommodating insect holes + the fraction of trees in path with rot unseen below the surface). |
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Drill a whole set of holes and wait. |
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Hurricanes aren't nearly as quick as tornadoes for
wind velocity. |
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//two contra-rotating tornadoes, one contains a straw, the
other one has a plank// |
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Which one has the sharks? |
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[ RayfordSteele] Your right but i don't think the straw would know the difference. A straw is a tiny arc of the tornado's rotation. |
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I might be grasping at straws here, but I found bamboo
straws, they do look very rigid and have more mass.
You can get sharpened ones. Link. |
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A lightning strike on an old oak tree across the street one night left a rotten twig driven a half inch into an age-hardened 2x4 porch rail when I was living in upstate New York - that's all I got. |
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