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# Driving a straw though piece of wood

 (+1, -1) [vote for, against]

Easy to do, all you need is 1 straw, 1 plank and the patience to wait for tornado season.

If you flub it first time, it's ok, there's always next year.

 — not_morrison_rm, Jan 23 2019

Mythbusters gives it a try https://mythresults.com/episode61
[RayfordSteele, Jan 24 2019]

Nerf dart through a plank https://www.youtube...watch?v=s2yIMJ4iayg

Wheat mechanical properties https://ac.els-cdn....a8f791513f83c2dc4d2
[bs0u0155, Jan 24 2019]

Bamboo straws https://www.flavour...ducts/bamboo-straws
Found a great pic of a very sharp one, but couldn't find it again [not_morrison_rm, Jan 27 2019]

It turns out this is pretty easy if you drill a hole in the piece of wood first
 — hippo, Jan 23 2019

 The thing is, a tornado will not drive a straw through a piece of wood.

 Consider for a moment. Suppose the straw is moving at 200mph, and the plank is standing still. The straw hits the wood at 200mph.

 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.

 Now, what will happen in the second situation? And therefore what will happen in the first situation?

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.
 — MaxwellBuchanan, Jan 23 2019

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.
 — hippo, Jan 23 2019

 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".

Later edit - ignore my ego, I try to.
 — not_morrison_rm, Jan 23 2019

If wind blown straw was capable of such ballistic superpower you'd see whole pastures full of dead animals.
 — doctorremulac3, Jan 23 2019

 //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?

 Mate.

Or perhaps the military have been missing a trick, and should be developing low-velocity straw bullets.
 — MaxwellBuchanan, Jan 23 2019

 //developing low-velocity straw bullets.

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.
 — not_morrison_rm, Jan 23 2019

Does the environment of 300 odd mph of laminar hurricane air around the straw count?
 — wjt, Jan 23 2019

Never heard of straw through wood but wood through concrete during tornadoes and hurricanes is well documented.
 — 2 fries shy of a happy meal, Jan 24 2019

 //Consider for a moment. Suppose the straw is moving at 200mph, and the plank is standing still. The straw hits the wood at 200mph.//

You're forgetting about the headless nail super-glued to the front end of the straw [Max].
 — Skewed, Jan 24 2019

 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.

 I also just watched a YouTube video of a Nerf dart being fired through a 3/4 inch plank. See link.

So I won't say that this is definitely possible, but I'm don't think Mythbusters busted the myth completely.
 — scad mientist, Jan 24 2019

Nope. No hits for straw through wood. Maybe that's why the last little piggy built from other materials.
 — 2 fries shy of a happy meal, Jan 24 2019

 //Meanwhile, in a well-sheltered basement, a man has another plank and another straw.//

Ah, those long winter evenings.
 — pertinax, Jan 24 2019

Planks constant?
 — 2 fries shy of a happy meal, Jan 24 2019

 //Is it possible that a straw could end up traveling faster than the maximum measured wind speed?//

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.
 — MaxwellBuchanan, Jan 24 2019

 Ok, last try....two contra-rotating tornadoes, one contains a straw, the other one has a plank.

Or, maybe I'm just grasping at straws?
 — not_morrison_rm, Jan 24 2019

 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.

 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?

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.
 — doctorremulac3, Jan 24 2019

 //Anybody know what speed the straw would have to be traveling at to punch a hole in the board?//

 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.

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?
 — MaxwellBuchanan, Jan 24 2019

 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)

 I'm uneducated, not stupid.

Anyone else wanna give it a shot?
 — doctorremulac3, Jan 24 2019

 //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.//

 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.

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.
 — bs0u0155, Jan 24 2019

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.
 — hippo, Jan 24 2019



 OK ... it's not just about mass, or projectile shape, or projectile material. It's what clever people tend to call "very complicated" ...

 There are a huge range of ammunition natures, for everything from .22 rimfire pistols to 15-inch naval rifles with a range or 30km.

 In each case, the choice of projectile must take account of the specific characteristics of the target.

 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).

 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.

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.
 — 8th of 7, Jan 24 2019

 // 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.

 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.

 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.

 But it gets worse.

 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.

 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.

So, I think that sort of answers it.
 — MaxwellBuchanan, Jan 24 2019

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...
 — hippo, Jan 24 2019

 My bet's with that as well, but what about say, 25,000 MPH in a vacuum?

 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.

 By the time I wrote this, twenty posts had popped up rendering everything I said unnecessary.

 Time for an idea.

//rendering everything I said unnecessary.// (Boy did I set myself up with that one.)
 — doctorremulac3, Jan 24 2019

 // I didn't say you were stupid, [doc], or even uneducated. //

 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 ?

 // fastest non-sub atomic particle object we've accelerated on Earth? //

 NASA has an impact simulator that launches metal spheres at stupid velocities to investigate cratering phenomena. That probably still holds the record.

 On impact, the sphere instantly converts to plasma.

 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.

You need to parameterise your question a little more closely.
 — 8th of 7, Jan 24 2019

I strongly resent the implication that I would ever give either of my brothers \$3.
 — MaxwellBuchanan, Jan 24 2019

 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.)

 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:

 1- The straw would vaporize and...

 2- This takes place in a vacuum.

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?
 — doctorremulac3, Jan 24 2019

 To a very rough approximation, you can estimate it as follows.

 (1) Assume that 10 grams of wood is to be vaporised.

 (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.

 (3) Mass of straw is, say 10 gram (0.01kg).

 (4) E=mvv/2, so v=root(2E/m), or 1400m/s.

 Or, in old units:

 (1) Assume that 21/64ths of an ounce of wood is to be vaporised.

 (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.

 (3) Mass of straw is, say 21/64ths of an ounce (0.021lb)

(4) E=mvv/2, so v=root(2E/m), or 6.96 furlongs/s. That's about 3100mph.
 — MaxwellBuchanan, Jan 24 2019

 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.

I'll put that on my someday weekend project list.
 — doctorremulac3, Jan 24 2019

I may have dropped a factor of 64 somewhere.
 — MaxwellBuchanan, Jan 24 2019

 (...wonders if the MOD would be interested in some 50ft straws orbiting the planet?

Ideal for assassinating enemies who habitually live in single-plank constructed buildings (bit of a niche market I have to admit))
 — not_morrison_rm, Jan 24 2019

 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.

 // I strongly resent the implication that I would ever give either of my brothers \$3 //

Sorry, Zimbabwian dollars - should have made that clear.
 — 8th of 7, Jan 24 2019

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.
 — MaxwellBuchanan, Jan 24 2019

That's doable with something like an SR-71. Instead of rods from god, you could get away with chopsticks from 120,000ft
 — bs0u0155, Jan 24 2019

 //Zimbabwean currency bills

...will be regarded as a hard currency after Br**it, so, keep your put them in a safe place.
 — not_morrison_rm, Jan 25 2019

 As [hippo] indicated and I have been thinking about this too much. Is this a straw velocity?

 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).

Drill a whole set of holes and wait.
 — wjt, Jan 25 2019

Hurricanes aren't nearly as quick as tornadoes for wind velocity.
 — RayfordSteele, Jan 25 2019

 //two contra-rotating tornadoes, one contains a straw, the other one has a plank//

Which one has the sharks?
 — pertinax, Jan 27 2019

[ 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.
 — wjt, Jan 27 2019

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.
 — not_morrison_rm, Jan 27 2019

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.
 — normzone, Jan 28 2019

 [annotate]

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