1 like = 1 engineering fact I think is weird and cool, and possibly not general knowledge
Not limited to computers
Concrete is pathetically weak under tension and can't be horizontal without support
Concrete spars are made with a steel I-beam cranked up to Gigapascal tension, with concrete poured around it. When releases, the steel compresses the concrete far beyond load tension
A dangled wire doesn't form a parabola; it forms a catenary. Incidentally, a catenary is also the path that gets an object rolling down it to the end the fastest.
Rural electricity is commonly delivered single-phase over just one wire. The return circuit is formed by the planet.
The circuit endpoints drive big stakes into the ground and boom, free return wire
We still have no better electrical generation method than "heat up water and use it to spin a magnet"
Nuclear reactors are just the biggest teakettle on the planet
The British power grid coordinates commercial breaks with the BBC, because they have a dedicated reactor that spins up 1min before the commercial starts and the entire goddamn country gets up and puts the kettle on.
If they don't, the country browns out.
NASA rocket design constraints are directly influenced by the hip width of Italian horses.
Thread's gonna fork for this one.
Back to weird engineering facts.
The reason Roman concrete architecture still exists is due in no small part to the destruction of Pompeii.
When they found what happened to the city, they realized volcanic ash would be a great addition to the mix, and it was.
The Florence cathedral is the largest free-standing dome mankind has ever made, and it uses an inverse catenary arch to support itself.
Brunelleschi didn't even have to shut down the church in order to build it.
Read up on Il Duomo it's fucking amazing.
The reason Babylonian ziggurat, Mesoamerican ziggurat, and Egyptian pyramids all look the same is because they're built at more or less the repose angle of stone. They didn't trade notes; that's just how you build rock piles that don't fall down.
Inca walls don't have mortar.
Why they didn't invent mortar, I don't know, but the solution they used is one we use in carpentry. Cut slots in adjoining rocks and put a biscuit there to hold them both in place.
It's a lot easier in carpentry, but it works great.
Every domesticated organism has been genetically engineered for at least six thousand years to act in the opposite of its natural instinct.
Crops that produce huge fruits and don't disperse seeds fail in the wild, but are perfect for cultivation.
Metallurgy is so old and fundamental to human civilization that Sumer has a myth about how Enki created the first tongs, from which all other tongs were made.
In truth, the first tongs probably weren't tongs, but stone chopsticks.
One of the reasons stereotypical "Renaissance men" were so widely skilled was because musical instruments are insanely complex to engineer, and so being a musician was a requisite for practicing engineering. Same for music theory and mathematics.
The Navy used, and still has operational, geared computers that took in data about ocean and wind conditions in order to compute firing solutions for shipboard artillery. It took until the mid-70s in order for them to be displaced by electronic machines.
Notre Dame took 182 years to complete.
Nearly two centuries of continuous work.
Makes computing's ~50 years of legacy work pale in comparison, doesn't it?
The development of gears has done more for the advancement of human technology than any other pursuit, peered only by the transistor. Clocks and automotive drivetrains are some of the most complex compact systems humans have deployed in scale.
Submarines at depth use an Inertial Navigation System that is basically a very large ball in oil with springs surrounding it. When the sub moves, the ball's momentum doesn't change right away, and it pushes on the springs. This allows measurement of the momentum change.
We've refined the accuracy to the point that submarines can operate with <1ft of accumulated error over months.
Couple it with a good clock and you're done.
Naval research labs placed large masses of various metals on the seafloor in the '50s and '60s. Since then, the dissolved metals in seawater have precipitated onto them faster than the seawater has dissolved them, and they've grown significantly.
Remember these bad boys?
We test them on earth in a Helmholtz cage, which is like a Faraday cage but for magnetic fields. It's six coils (two in each axis) that can be tuned to create any field we want in the middle.
USN aircraft carriers are switching from steam-powered catapults to electromagnetically driven catapults.
That's right; USN aircraft are technically railgun projectiles.
Your office walls are probably white. This saves money on heating by reflecting the infrared light you radiate back onto your skin, so you only lose ~10% of your radiated waste heat per workday.
Speaking of light, photons don't travel through matter.
Lenses work because light strikes an atom and is absorbed, causing an electron to jump up a valence level. It takes non-zero time for that electron to fall back down, and when it does, it emits a photon.
(cont) in transparent materials, the photons emitted are twins of the photons absorbed. In colored materials, they're not.
It takes longer for a photon to travel through a thick material than a thin one, and that curves the wavefront.
Lenses also don't give you energy for free. You can't actually focus the source light to a single point, because that would violate thermodynamics. This is why you can't start fires through a telescope with moonlight, no matter how finely you focus.
You think trains go "click clack" because railways used to leave gaps between rail spars for expansion. We solved that by (a) building in the summer and (b) putting the rails under kilopascals of tension. This solves the buckling problem and the noise problem.
SCUBA regulators step air pressure down from 3-5 thousand psi to ~200psi above ambient using ✨magic springs✨ similar to injection valves in car engines.
They're also balanced in such a way that if something breaks, they slam open rather than closed.
SCUBA-qualified air compressors use electrostatic and chemical filters, as well as physical, because they must produce air that is PURELY dinitrogen and dioxygen, plus a noble gas like helium or argon. Any other particle or gas will kill you (faster).
Underwater heavy construction is done in diving bells, not in SCUBA gear, because it offers more space, air supply, and environment control.
They also fail catastrophically, from air poisoning or hull cracks.
Metalcasting leapt forward when it was discovered that quenching in urine lent desirable properties to the metal.
Urine has been used for leatherwork for a long time and it's no surprise that smiths looked into the matter. Sincerely not weird.
Let's get on theme.
Geosync orbit is 36 Megameters above sea level. That's REALLY HARD to reach with a rocket, so we basically don't.
Geosync satellites are often dropped at about ~500km, and then turn on a motor and accelerate sideways.
Satellites in low earth orbit have ~90 minute orbital periods, with ~30 minutes in full eclipse and ~60 in some sunlight. This causes an annoying thermal cycle, causing the metal in the computers to do weird things like grow whiskers.
Whisker growth is a combination of crystal impurities, vacuum, and thermal cycling. The metal traces in PCBs or wires can grow hairs that cause shorts and kill the satellite. We mediate this by spraying plastic coating over everything, so the metal has nowhere to go.
Eli Whitney's cotton gin is the classic example of industrial agriculture, but in truth it's the plowshare that revolutionized farming. Once we moved past the classic medieval yoked plow into more complex designs, productivity per person exploded.
Complex plows required industrialized metalworking, which is why they didn't appear until the late 1700s. They were further empowered by the spread of combustion engines able to replace animal labor, in the mid 1800s.
Gold is the quintessential metal for currency because it's fucking useless until you reach modern electronics. Gold also doesn't tarnish and can't be faked, which help.
Gold alloys easily without changing color, though, which is how material density got discovered.
The easiest way to dilute gold money is to melt it, mix in other metal, and recast. But, other metals are lighter, so the alloy is less dense. Equivalent mass will be larger; equivalent volume will be lighter.
This was discovered by Archimedes, though it is not his eponymous principle. Archimedes' Principle is what keeps boats and zeppelins working. Archimedes used it as a solution for a (likely hypothetical) question about determining gold adulteration.
There is no one orbital velocity. Orbital velocity is determined by your distance from the surface of the earth. Low-earth orbital velocity is ~7-8 km/s. Geosync (way way up there) is ~3 km/s.
We consider space to begin at 100km altitude because that's where the air becomes so thin that the speed required to maintain aerodynamic flight surpasses the orbital velocity at that height. It's harder to be an airplane than a satellite here.
Also, you're wrong about how airplanes fly. I'm assuming you're wrong because my dad is a lifelong pilot and aviation instructor and fucking HE was wrong.
Air atop the wing doesn't speed up because it has longer to travel. Air doesn't entangle; streams don't care about rejoining
Wings are (simplifying a lot) two wedges. One points up, one points down. The bottom surface shunts air downwards, which equal/opposite reaction shunts the airplane up.
The top surface directs the air up slightly, creating a low pressure pocket on the back half of the top.
The downward shunt is a lot stronger than the upward, so that provides positive lift.
The low pressure on the back half of the wing makes room for the wing to BE pushed. It doesn't produce suction any more than a jet engine does (hint, nearly none)
We divide common radio into AM and FM because those were the first methods of encoding analog information into light beams that we found.
XM radio uses the X to sound cool but it's actually PM. The P stands for Phase and it's ... weird math. Wikipedia has a decent article on it.
Am I at 50 yet? I should've numbered these.
Whatever, I'm at work for another hour.
Let's go back to civil engineering; I want to stretch those memories.
Pipelines have a bad rep but this country is literally built on them.
Like many things in civil engineering, modern pipelines have a Roman heritage.
BTW, Roman aqueducts are a testament to a cultural distaste for experimentation and easy access to labor.
They don't need to exist.
Specifically, Rome said "water can't flow uphill, so we're going to make a continuous downhill slope from the mountaintop collection points to our cities, and it will never go uphill ever" and made the aqueducts to fit.
Water will flow uphill.
It won't flow higher than the entry point, obviously, but if you take a hose and let it dangle into a U shape, and pour water in the higher end, it WILL flow out of the lower.
A common tax evasion scam in Rome was to sneak into aqueducts and widen the pipe
You were taxed based on the water flow designated in the aqueduct plans; they didn't have usage meters like we do. Widen your pipe on the down-low, get free water.
Unfortunately, the pipes were made of ... lead. So that didn't go great.
American pipelines are actively driven, none of this gravity-fed weak sauce.
The downside of this is that the mass you have to drive into the pipe to maintain pressure is directly proportional to travel distance.
So our pipes have locks every so often, to allow sections to be sealed and removed from the pressure drive system.
Pipelines carry multiple fluids by using a big plastic/rubber plug to separate them.
I beams (shaped like ][ ) are used because the wide top and bottom resist torque, the load goes through the centerline, and the rest of the beam does no work. The beam performs better without the excess mass load, even.
The reason we put vertical steel rods in concrete, without tension, is because while concrete can tolerate absolute compressive force, it is less good at compressive pressure. The steel takes disproportionate pressure load while the concrete handles most of the force.
This allows for a reduction in pillar size without sacrificing overall load-bearing capacity. Furthermore, sideways forces are distributed through the steel rod, reducing likelihood of cracking from those loads.
Call this 51. The flying buttress was developed in Gothic architecture to hold up massive cathedrals whose roof and wind loads would otherwise blow out the walls and collapse. It's what enabled the advent of buildings with such massive open interiors.
52. While sprung siege engines, such as the onager, ballista, and catapult, have been known since antiquity, the trebuchet is the first European counterweight-driven engine and vastly changed the field of warfare.
53. Speaking of artillery, WWII-era battleships had guns up to 13" caliber firing half-ton projectiles. This is a mass on the order of a Volkswagen Beetle. We stopped doing this on boats when we got better at aerial bombardment.
54. Commercial aviation is a miracle of scheduling and planning to rival the actual engineering of the planes. I have mad, mad respect for the people who make the complex web of flight plans across the country and globe work.
54 cont: Flights are loaded with fuel to optimize fuel usage and efficiency for the trip. This requires assumptions about plane weight, and if the plane is underfilled it performs *worse*. This is why I flew for free until last year.
54 cont: If Delta could get another 150lb on the plane, it would raise the engine efficiency and save fuel, so even though I didn't buy a ticket I was still saving them money. Perks of having two parents in the aviation business.
55. Commercial lumber is impregnated with copper particles in order to make it toxic to rot-inducing microorganisms. This is done in a high pressure treatment which also improves the lumber's structural properties.
56. If you live in America, your floor (if not at ground level) is probably rated to support flooding of no more than seven to eight inches of water. In fairness, seven inches of water is really heavy.
57. Most residential lumber is one of a couple species of pine or fir. These trees grow straight and at a reasonably rapid pace. These woods are soft and flexible, which is one reason houses creak, but they're very hard to actually break.
58. Skyscrapers sometimes have a hidden pendulum in the center column that is used to offset wind loads. This can also be used to reduce vibration from earthquakes.
59. Diesel trains are not trucks. The diesel engine runs a generator, and the train is powered by electric motors. Electric motors are vastly superior to mechanical transmissions at delivering high torque at low RPM.
60. Clutchless transmissions are two fans in very thick liquid and it utterly amazes me that this is an effective method of torque delivery. Clutched transmissions use friction between two very smooth plates so tldr cars are weird.
61. Front-wheel-drive cars have a torque penalty during initial acceleration, but since you're not a street racer, that's an acceptable trade-off for improved handling.
61 cont. Engines shouldn't be in front of the passengers, but they have to be in order to weigh the front end down during startup. Engines don't crumple, so that makes head-on collisions less pleasant.
62. The tolerance between piston and piston-chamber in engines is on the order of three thousandths of an inch. The piston expands and narrows this to ~ one thousandth when the car is hot.
Keep that shit oiled; you have no idea.
63. Hard drives operate on nanometer-order gaps, which is as far below thousandth-inch as thousandth-inch is from our scale*. Don't rattle your hard drives. Also, use solid state.
*more or less
64. It's cheaper and easier to ship a truck carrying a vat of molten aluminum across the city than it is to melt your own aluminum, at scale.
65. Aluminum and glass foundries take a week to turn off or turn on. They specifically use materials with high specific heats for both safety and efficiency.
66. Bauxite refining is 20x as energy-intensive as recycling aluminum, per unit mass. Recycle your pop cans. I don't know the stats for glass off the top of my head, but recycle bottles too.
67. Plastic 2L bottles have really good structural integrity, since they're built to withstand some fierce pressure differentials.
They can be, and are, used as building bricks for earthworks.
68. Plastics are an amazingly versatile and useful materials family with a variety of properties, one of which is near-indestructability.
The fact that we use them for disposables is a travesty.
69. Condoms and other sex products have intensive materials standards and manufacture/testing procedures, *obviously*. It sucks that the end result is considered taboo, because they take an impressive amount of work to create.
70. If you heat a metal ring, the inner radius expands too. This is one way to fasten rings to shafts without bolts: heat the ring, slip it over the shaft, then let it cool and it will shrink and lock in place.
71. Mechanical linkages can be designed to turn a constant rotation into either straight linear motion, or constant linear speed, or trace complex polynomials, and we've been doing that for three or four hundred years.
73. Because water is incompressible, it be used as a hammer or a knife on materials that are too strong to be struck or cut by normal tools. It's energy-intensive, but you can do it.
74. Multiple thinner cables twisted around themselves are significantly better than a single straight cable, whether we're talking about tensile strength in steel or signal conductivity in copper. Fun coincidence.
75. Electrons move about an inch, tops, in AC conductors. The field moves at about ⅓ to ½ the speed of light as the electrons jostle back and forth, but the electrons themselves don't travel much.
76. Clay embedded with ferromagnetic particles make better magnets than straight up metal blocks, because they're easier to shape and the domains are easier to align. Metal crystals have a lot of internal cancellation.
77. Tape measures are built to the optimal performance characteristics to be used as radio antennae and this is a real thing that satellites do. They're self-straightening, easily stored, and machined to high uniformity.
78. I thought this thread would be over at, like, 40. I was not prepared for this.
My job title says engineer so technically this counts.
79. Tandem-rotor helicopters exist and are very cool. They are more stable and powerful than the design you generally think of when you think "helicopter"
80. I'm canceling this thread at 100 okay do you know how much work it is to come up with these off the dome?
81. Any signal over time can be described as a sum of sine waves with various multipliers. This description is called a Fourier transform, and is a key principle in electrical science.
82. If you think time zones on the planet's surface are bad, you should see time zones distributed across a processor, since these things operate so quickly that the speed of clock-tick propagation is slow enough to seriously matter.
83. GPS mathematics is one of the few intersections of general AND special relativity, 4-D hyperbolic geometry, orbital mechanics, and time dilation. Speed-of-light lag is in there too but everyone deals with that anymore.
84. I at least consider engineering success when it moves from singularly impressive to commonly banal.
Electricity, plumbing, communication, navigation, travel, shelter, resource distribution are so incredibly trivialized in modern societies, like, WOW
85. The grid system, while appealing, is hilariously bad at actual traffic routing which is one reason it never appears in systems which have self-optimized for traffic delivery, like your bloodstream and nervous system.
86. Metal structures in environments with acid rain or seawater exposure will have a sacrificial metal of some other metal, often bronze, painted over them to take the induced electrical damage without corroding the actual structure.
87. Asphalt roads can be stripped, recycled, and replaced in a single pass as long as the underlying gravel/rock bed is not significantly damaged.
88. Last I read, and remember I'm not looking these up, humans move a Gigaton or so of earth every year in construction and mining projects. That's about four or five Panama Canals.
89. The Great Wall is not visible from space. It's very narrow. The Kennecott Copper Mine in Salt Lake City is; it's wide and a very different color from the surrounding terrain.
90. Surface mining basically scrapes the entire dirt and rock off the top of a mountain, sets it to the side, pulls out the ore, and pushes it all back. A lot more energy used, but safer and more thorough than bore mining.
91. Mining vehicles are typically assembled, operated, and disassembled all on site, and never go anywhere else as themselves. Also, look up pictures of those monsters.
92. The space objects closest to earth are the cast-off intermediate stages of rockets destined for higher shells.
93. The longest tape measure ever built is the laser array we aim at shiny mirrors Apollo astronauts dropped on the moon.
94. In one tick of a modern CPU, light travels about eight inches.
Sometimes I think about the fact that Intel is about knocking on the resolution limits of the physical universe and honestly I don't know how to handle that.
95. This isn't engineering, but I think it's cool. There's a small window when throwing a ball where if you let go, it will go where you want. This window is far smaller than the time it takes to process and issue the "open fingers" command.
95 (cont) In fact, your brain has to decide "time to open my hand!" about ten or twenty milliseconds before your hand enters the window; long before you even see that your hand is in the right spot.
95 (cont) If we scale this up, it's like standing on the roof of a ten-story building, listening to a song playing on the ground below, then plugging your ears and going from memory to toss a drumstick off the roof and have it hit the drum kit below on the right beat.
96. Electricity is delivered in tri-phase because it converts to single-wave or DC more smoothly and with less voltage drop than pure single-wave does, and a short between two wires is slightly less awful than a short in single-wave.
97. An arc between all three lines of high-phase tri-voltage creates a UV arc of sufficient intensity to cause sunburns and blindness in onlookers. Great YouTube clips though, as long as you get the ones where nobody dies.
98. Safety glass is manufactured under internal tension so that if it starts to crack, it rips itself apart into tiny little pieces rather than allowing natural fault propagation that results in horrific shards.
99. The gold leaf commonly used to decorate churches is micrometers thick. Gold's ductility is such that it can be formed into very thin foil or wire without breaking, without significant infrastructure.