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  • Steel from pre-1945 (the atomic events) is valuable as source materials for radiation-sensitive equipment, like Geiger counters. Almost all other sources of iron is contaminated somewhat.
  • Power goes from power source to load through electric fields, not the wires connecting the power source and the load. Wires just direct the electric field to the place you want: "When the battery is connected into the circuit, even with the switch open, charges rearrange themselves. ... Charges build up on the surface of the wires. The charges rearrange themselves until the electric field is zero everywhere inside the conductor. There is an electric field outside the wires due to these charges, but it's zero inside the wires. ... When we close the switch, ... the electric field inside the conductor is no longer zero, ... the new electric field from the modified surface charges radiates outwards at essentially the speed of light, and when it reaches the bulb, the electric field inside (the wire) is no longer zero, so current starts to flow here too."
  • "Like all in-ear headphones, the soundstage of these headphones is bad. This is because creating an out-of-head and speaker-like soundstage is largely dependent on activating the resonances of the pinna (outer ear). The design of in-ears and earbuds is in such a way that fully bypasses the pinna and doesn't interact with it."
  • Japan has 50Hz (East Japan, German equipment) and 60Hz (West Japan, American equipment) AC in the same country. This one country makes a) many electronics work with 50-60Hz, and b) many database schema designers go nuts.
  • Anti-tank missiles and shaped charges pierce through tanks, so tanks need heavy armour. But heavy armour impairs a tank's ability to move quickly. So the military geniuses came up with reactive armour, lightweight pads of explosives that blow up to deflect the concentrated damage caused by shaped charges. Knowing that, the same military geniuses created tandem charges, which are multi-stage missiles, with the first stage designed to blow up and deactivate the reactive armour, and the second stage is a shaped charge that penetrates the tank.
  • The moon is quite large: it is the 14th largest thing in the solar system.
  • Fires don't go through small holes ("quenching diameter"). That's one of the reasons why propane torches don't blow themselves up.
  • (Stainless) steel velcro lasts upwards of 500,000 pulls.
  • The radius of the observable universe is about 46.5 billion light-years... but the Big Bang happened 13.8 billion light-years ago. Assuming the numbers are more or less accurate, clearly the universe is expanding faster than the speed of light.
  • Spectralon is the world's whitest thing. After that, it's Erin Conrad, who claimed to be so pale.
  • Running AC motors on modified sine wave can cause waste heat to accumulate. Other devices tend to work just as well on modified sine wave as they do on pure sine wave.
  • Given what the big bang is (there was space), spacetime must have been all time, then, right? Alternatively, since there was no time, there was no space either... and there was no "before the big bang".
  • High-impedance headphones, which are headphones greater than 50 ohms in resistance, are more protected from high-power audio equipment than low-impedance headphones. However, with high-impedance headphones, the sound might sound quiet if the source is low-power.
  • No known physical model can describe behaviour above 10^32 K. Something about gravitational forces becoming as strong as electromagnetic and nuclear forces.
  • There are air conditioners that freeze ice during off-peak hours to help you use AC with minimal electricity during on-peak hours.
  • People don't have home gravity battery systems because the energy density is almost bullshit.
  • Zoom lenses are often varifocal, i.e. if you change the zoom, the focus point also changes. More expensive movie lenses are parfocal, whose focal points and zoom can change independently.
  • Ultrasonic humidifiers send minerals in the (hard) water along with the mist, creating a white film on everything. It also triggers smoke alarms because of the increased particle count. Simple wicking evaporative humidifiers [of sufficient size] might work the best!
  • Solar winds wiped out Mars' atmosphere. Mars has no global magnetic field to protect it against solar winds, but a device to protect it is cheaper than you think.
  • Using a fireplace draws cold air in, making the home colder. The majority of the heat produced goes up the chimney, which you don't enjoy.
  • The farther apart the device is from the wireless charging pad, the hotter it gets (as long as it still charges).
  • At the middle of the milky way is Sagittarius A*, a supermassive black hole.
  • Blue light looks blurrier than red light because light of different wavelengths focus at different distances of the eye. Blue light focuses before red light. This leads to an optical illusion called chromostereopsis, where blue objects appear closer or farther from the screen than red objects.
  • Glass does not filter all UV. Of the UVs that your glass needs to worry about, UVB is completely absorbed, but UVA passes through (UVA is also harmful). Incidentally, UVB is the kind of UV that the body needs to make vitamin D.
  • Flash memory relies on quantum tunnelling to have electrons leak into places that they don't normally go. Watch a video on evanescent coupling or Zener breakdown. This is also why flash storage will start to lose memory after something like 10 years... because electrons can leak out even though there is no logical way for them to do so.
  • The ISS' orbit is never directly over the arctic or the antarctica.
  • Guilt-tripping people doesn't work. Looking at you, PETA.
  • Quantum computers return a single answer by making all incorrect answers destructively interfere with each other.
  • Three perpendicular polarizing filters let in more light than two. It might just be the first filter shifting polarity of the light going in, but I don't know.
  • The ISS is protected by whipple shields. Particles gradually decrease in kinetic energy and (hopefully) end up bouncing between two of its nets.
  • If someone sneezes in front of you, it can linger for like 40 seconds while travelling in your general direction. Droplets can eventually reach 6 metres from anyone not wearing a mask.
  • Geothermal power plants do not pump anything up. They allow superheated fluids to come up by itself. They then pump cold fluids back into the ground (using some of the power they generated from the steam) to replenish underground fluid levels.
  • Visible light is in the 1-petahertz frequency range.
  • Eddy currents (you know that ball-down-the-metal-pipe experiment?) are used to make brakes for trains, trucks, roller coasters, and fitness equipments. The energy is dissipated as heat.
  • Because of gravity, (for anything bigger than single atom,) the bigger something is, the more likely it is for that thing to be round.
  • Little Boy was a uranium bomb, while Fat Man was a plutonium bomb. There was also a Thin Man in the series, but that was never used on Japan.
  • It is best not to plug in your phone's charger while the phone is already plugged in... but since doing so requires deliberation, you are probably safe.
  • If you completely cover your roof with solar panels, some 16~20% of energy is absorbed and becomes electricity rather than heat. Did you know... Tesla makes solar panels that look exactly like conventional tiles?
  • The sun emits anything from x-rays to radio waves, but it emits a lot more IR light than UV light, which is why you rarely die by star damage.
  • "HEPA filters (on a plane) capture virtually 100% of particulates (like the coronavirus)." - NASA. "Fucking bullshit." - Paraphrasing Transmission of (SARS) on Aircraft, The new england journal of medicine. Leaving the middle aisle empty does almost nothing. People died literally seven rows down the aisle. People in the same aisle die first.
  • James Maxwell theorised electromagnetic waves, and Heinrich Hertz discovered it. Asked about the applications of his discoveries, Hertz replied, "Nothing, I guess."
  • Magnets lose magnetism at the Curie temperature before they melt.
  • 5G mmWave does not require line-of-sight because it can bounce off buildings and walls and billboards... but it also means you definitely won't be able to use it indoors if the window is closed.
  • USB sticks might get lighter or heavier as you store data in it, depending on the type of flash memory it is using. For memory that stores 0 with a charge, the USB stick gets lighter.
  • Stiction is a made-up word for "static friction".
  • Ionisation of air is blue because ionisation of nitrogen is blue. So, electricity, if you can see it, is often blue.
  • Charging a laptop (10.8V) wirelessly would be a huge waste of energy.
  • Some things orbitting the sun, like Ceres in the asteroid belt, meet more criteria for being a planet than pluto does.
  • A tough material absorbs energy and deforms instead of cracking. A hard material increases wear resistance. A knife should be tough (not put shards in your food) and hard (not need sharpening so often). You can also somehow create materials that are tough and also hard... somehow.
  • An impact driver, which looks pretty much like a drill, can drill much more effectively than a standard drill. It is designed to work as a screwdriver, not a drill. A drill is a drill, and can work as a screwdriver, just not as well.
  • "If you want (making an air purifier with a box fan) to actually work, you take a box fan, and 2 filters. You make a triangle and then some cardboard on the top and bottom to fill the gap. This increases surface area and reduces the stress on the fan due to pressure drop. Slapping a filter directly on to the box fan is going to kill the fan very quickly." https://i.imgur.com/SX1RloH.jpg
  • The universe is at least 250 times bigger than the visible universe.
  • The big bang was not a theory that the universe started from a big bang, but rather the inflation of space where this universe came about. It have the concept of singularity though, which says all the matter in the universe was at one point in spacetime (but not zero size). Other things? They don't know, and they don't try to explain them.
  • Granite is more naturally radioactive than a nuclear facility allows to be artificially radioactive. "If you took granite or marble countertops from most homes and installed them into a nuclear plant, they would have to be disposed of as nuclear waste after the next break room renovation." - /u/NotAPreppie
  • When you have a few billion of something, it can have massive effects on the world. If 5 billion people use your app, your app's efficiency can affect CO2 emissions in the order of megatons,
  • Only buy knives that claim a rockwell hardness of between 55 to 60.
  • It's not about sharpening. Some knives just don't stay sharp. That's why you need good steel.
  • Some people might say the mass of an object increases as its velocity increases. It's not true (but I didn't finish watching the video to know why because I had to poop).
  • Light as no mass. p = mv, i.e. m = p/v, does not work for things travelling quickly. p = γmv does. You can still use p = h/λ though... and if you have a solar sail, which is not travelling as fast as light, you can convert that massless stuff into velocity you can see.
  • Pool aerators pump bubbles into the pool, which break the surface tension of the pool, making it less painful if you fall into the pool.
  • The molar mass of water is 18g/mol, and the molar mass of dry air is 29g/mol, so adding moisture to dry air reduces its molar mass, and, thus, the density of the air.
  • The air inside snowflakes reduces sound travel.
  • CO2 only comes out of coke's nucleation sites, where the bubbles themselves are nucleation sites. Flicking the can/bottle removes bubbles from the side of the can/bottle, so the number of sites decreases, disarming the can/bottle.
  • During winter, cold air outside can be 50% relative humidity, and warm air outside can also be at 50% relative humidity, but cold air holds less moisture (think why cold glasses fog up) so the cold air has lower absolute humidity than the warm air. To increase moisture in your indoor air (if your room is too dry), lower the temperature or use a humidifier. To decrease moisture in your indoor air instead (if your room is too humid), draw in cold air, turn up the heat, or use a dehumidifier.
  • There is a hexagon at Saturn's (north, whatever that means) pole. All solar planets' "north" poles are decided by the earth's idea of "north".
  • Two galaxies can move away from each other faster than light... because "two galaxies ... are not travelling through space, it is the space between them that is expanding."
  • Objects spin in the axis with the maximum moment of inertia ("farthest center of mass"), which is stable. Minimum amount of inertia is also... okay. But if you have something that has three different axes (like a tennis racket), it will alternate between the first and third axes.
  • Moon phases occur not because of shadows cast by the Earth, but where the sun is when we look at the moon. If the moon is right in front of the sun (i.e. earth-moon-sun), then the moon we see is completely dark. Likewise, if the moon is aligned behind the earth (i.e. moon-earth-sun) without overlapping, then you see the whole moon.
  • Aerogel sounds like metal when dropped.
  • Jupiter's red spot is about the size of the Earth. It has 79 moons, more than the sun has planets. Inside Jupiter you can find gaseous hydrogen, liquid hydrogen, and metallic hydrogen layers.
  • Quantum supremacy is a specific term describing quantum computers being able to do work better than normal ones.
  • In free space, teleportation appears the same as travelling at the speed of light. In real life, teleportation has the advantage of being able to enter closed spaces.
  • Portable air conditioners with two hoses (instead of one or zero) are more efficient. Those with zero hoses are just useless, one pipe takes cool air from the inside, which requires it to work harder, AND creates negative pressure in the house, which sucks hot air in.
  • Apart from personal preference, there is no point setting your phone UI to pure black instead of dark grey, in the name of saving energy on an AMOLED screen. In this study, the difference in power between black and dark grey is along the lines of 1.5mW.
  • Circular floaters (in the eye) are brighter in the middle because of Poisson's bright spot, something Poisson didn't even believe in, says that light (as a wave) constructively interferes with light diffracting around each side of a circular object.
  • Glass is an amorphous solid. So no, it is not a liquid. You can tell glass doesn't "flow" or eventually distort by looking at hundred-year-old optical instruments, which still work.
  • Microwave grape plasma is due to, in short, microwave, which has a wavelength of 1.2cm in water, getting trapped inside the grape. When two grapes touch, the energy is trapped right in between instead.
  • The kilogram is (after 2019) defined using the planck constant. This means the kilogram requires the Metre and the Second to be defined. With the second being defined by the caesium-133 frequency, and the metre being defined as the distance light travels after a second... the caesium-133 atom (the stuff we use in atomic clocks) is actually the element with the most impact on the stability of the SI units.
  • An incandescent lamp's lifetime is roughly proportional to its operating voltage V ^{-16}. "This means that a 5% reduction in operating voltage will more than double the life of the bulb, at the expense of reducing its light output by about 16%."
  • No one builds jello pools because, firstly, the temperature required (first boil a pool's worth of jello... and then cool it, but not freeze it) is hard to control; and secondly, after all that effort, jello breaks.
  • An electron and positron spin together to form a positronium, an unstable state. When they annihilate each other, they turn into two or three photons, depending on their spin states.
  • Quantum fluctuations pull the universe apart. Assuming the theory holds true, specifically the vacuum energy part of it, this explains why galaxies are moving away from us faster and faster.
  • The Earth is actually closer to the sun during the northern hemisphere's winter. Seasons are largely affected by the tilt. Also, most of Africa is in the southern hemisphere, if you haven't noticed already.
  • Only robots sink in lava. Humans don't sink into lava.
  • Short gamma ray bursts are generated when (including) neutron stars merge. Long gamma ray bursts are generated when supernovae collapse into a black hole. Theories even suggest maybe there isn't much more life in space because GRBs are killing lifeforms on a regular basis.
  • Cold water is audibly different from hot water. (That means you can hear the difference between the two being poured, and you know which is which.)
  • At 194 dB or dBA (dB adjusted for the human ear), sound waves become shock waves.
  • Olber's Paradox: since there are lots of stars in the sky, can nothing stops photons from coming to us, we should see a bright sky. But it's not the case because the universe is not infinitely old, and the photons from these stars don't have time to arrive to us yet.
  • Time dilation can also be thought of as length contraction. An object that is travelling at the speed of light towards you, also thinks you are travelling at light speed towards it. And you look just a fraction of your actual length dependent on your speed. This allows muons, which would normally only travel 500m before going away, to travel 10km worth of atmosphere. Time dilation is relatively insignificant unless you're travelling at >70% the speed of light.
  • Shutter speed and exposure time, being synonyms, are both units of time.
  • Noise reduction by averaging two photos only reduces noise by the square root of the number of measurements.
  • The unit Kelvin does not come with the word "degrees" because it is considered absolute. Also, Since the triple point of water is at 273.16K but 0 degrees Celsius is 273.15K, water actually boils at 99.974 degrees Celsius.
  • For paranoid people who think people can see them through walls, EMF shielding paints is for you!
  • Cold fusion exists. Muons ("heavy electrons") hold nuclei 200x closer together, making them much more likely to fuse, which means it can occur at room temperature. Unfortunately the input energy to generate a muon is still higher than the energy you get back from fusion, so it's still useless right now.
  • Drag has a square relationship with velocity. This makes "making a huge gun that shoots people into space" impractical.
  • Uranus (the 7th planet) is larger but lighter than Neptune (the 8th planet).
  • The original frequency of a signal is the fundamental frequency. Slight distortions of the original signal may also cause harmonic signals to be present. For example, if the fundamental frequency is 2 kHz, then the second harmonic signal would be 4 kHz and the third harmonic signal would be 6 kHz. etc.
  • A Decibel (dB) (10⋅log₁₀(Power out/Power in)) is indeed a deci of a Bel, which was named after a guy with the last name Bell.
  • Home voltages are between 120V to 240V. At least these are the figures reported by ISED Canada.
  • The voltage drop across a resistance can be measured with a volt meter across the terminals. If the current and resistance is known, voltage drop can be calculated using Ohms law: E = I R. (E =volts I = amps R= ohms).
  • The reciprocal of resistance is conductance. A circuit with high conductance has low resistance and vice versa.
  • Carbon is the most-commonly used material for building resistors.
  • The ionosphere is most ionised during midday, because that's when there is the most sun.
  • Taping windows during a hurricane does little to protect people, since glass is still glass, and taping only controls how big the shards are.
  • Liquid or liquid-like cargo can sloth inside the ship, making the ship less stable.
  • Capacitive touchscreens work with any conductor. They just need a big enough surface area to register as a proper finger.
  • A pulse that lasts literally no time is called a Dirac pulse.
  • Venus' atmosphere is 90 Earth atmospheres' worth of pressure. Most of the probes sent there imploded in midair.
  • GPS does not triangulate, says reddit man, it trilaterates. Trilateration does not involve the measurement of angles. "Where the signals overlap is where you are."
  • "Gravity warps spacetime", meaning it figuratively warps the axes on which we make measurements. An apple thrown up falls down can be considered travelling linearly upward at a constant speed, had there not been a gravity distortion of spacetime.
  • A preferred rotation of planets came about when all the planets going the other way got destroyed by the planets that go the other way. Whichever direction with more planets wins.
  • The larger the opening of a vacuum cleaner, the more powerful the suction is, according to Mythbusters.
  • Sound travels 5x faster in water, but more quietly, so you rarely hear anything unless it was loud.
  • "Triangular sails allow ships to sail into the wind as well as with it." - How It's Made episode about sails
  • CT scans are still X ray.
  • It is impossible to exceed the speed of light in a vacuum, but it is possible to exceed the speed of light in water, which is about 0.75c. When electrons do that in a nuclear reactor, a blue glow is emitted.
  • "Fun fact, in space fuses don't work well because there is no gravity for the melted bit to fall away, so they continue to transmit electricity until the fuse metal boils away or the equipment fails."
  • Centripetal force is the force acting on the center. Centrifugal force is the force acting outward on the flying object.
  • The Boomerang Nebula is the coolest thing in the universe. Not Pokemon.
  • "False vacuum" refers to the theory that the current space is just a local minimum of energy, rather than the global minimum of energy, and that a random event might instantly turn the universe into one with a lower energy, destroying the current one.
  • If a bridge is wavering about because of the people on it, then the people will try to adjust their stride to the movement, making the situation even worse.
  • A knuckle ball moves erratically because it isn't spinning.
  • Superluminal communication (communicating instantly through quantum entanglement) is believed to be impossible because, in a Lorentz-invariant theory, it could be used to transmit information into the past.
  • Running in the rain: given total rain rate = (rate from top * seconds outdoors) + (rate from side * seconds walking), you get less wet if you stand still from time A to time B, and less wet if you run from point A to point B.
  • Space movies almost never depict explosions correctly. There is no fire (or very little of it), the fragments would travel at the same speed as the vehicle they came from, and it would quickly extinguish because there is no air.
  • To the moon, the Earth is a thing in the sky that stays in position all the time.
  • The ISS is set to retire in 2020. Or 2024. Or 2028. Or...
  • The reason (microwaving your own fucking hand) is bad is because microwaves are primarily absorbed below the skin, thus bypassing the nerves. You could be literally cooking your muscles without ever realizing it.
  • String theory, integrating gravity with the point-in-space "standard model", is theoretically sound. In 10-dimensional space. Maybe it doesn't even make sense.
  • 75% of the mass of the universe is hydrogen, and 25% helium. The rest are insignificant.
  • The fastest object to be propelled by man, apart from trivial things like particles, was a manhole cover, at 0.02% the speed of light.
  • "...for every breath you take, there's a ... 99% ... chance that you're breathing in at least one molecule of Caesar's farts from his last day alive."
  • Fish are more conductive than fresh water, but salt water is more conductive than fish. This makes electroshocking impossible in salt water.
  • Infrared cameras, including one in a phone case, can reveal your PIN on any non-metal number pad, including the order of the digits, with 80% accuracy.
  • If the temperature gradient is large enough, power can be generated from the gradient using the seeback effect, which does not involve boiling water and turning a turbine.
  • Ultrasonic mosquito repellants do not work.
  • The event horizon is where escape velocity equals the speed of light. The photon sphere is where orbital velocity equals the speed of light.
  • UV light doesn't kill anything unless the light is applied for at least 10 seconds. The light also needs to be UV-C, the wavelengths that kill germs.
  • A planet gets tidally locked, as a matter of fact, if it's too close to a star. Because, you know, the water is pulled towards the star. So you can't just look for Earth-like planets near the right temperature---you need to look for the right size of star as well.
  • How fast a plane travels west/east depends on the wind direction, which is not always faster from east to west.
  • Microwaving a half-cut piece of grape yields plasma.
  • The 'speed of gravity' is the same as the speed of light. If the sun goes away, we also have 8 minutes (ish) of time before we are affected gravitationally.
  • No free (Android) app corrects fisheye images because it's hard.
  • By detecting the Earth's mass, magnetic field strength, and earthquake data, scientists conclude that the center of the Earth is made of solid iron, with liquid iron surrounding it.
  • We do not have enough nuclear weapons to blow up the moon. Even if we do, the moon would just clump back into a moon-size chunk.
  • Why does light travel? Because spacetime is a two-dimensional vector of a set length; an object can travel through space and time. In photons' case, they travel entirely through space, and not at all through time (which gives the impression that nothing can ever be "faster" than light). For ordinary, massive objects, they mainly travel through time.
  • Snowflakes can in fact be alike; the major factor is air turbulence, which can be controlled.
  • The HyperLoop doesn't work because the vacuum required is never going to be happen with all the stupid people around. (Imagine a loser poking a hole in the loop and everyone is screwed, or a dude throwing a stone into a turbine or something)
  • Steam can be used to light things on fire, simply by the definition of "steam is hot", if something is hot enough.
  • Solar eclipses occur pretty much anywhere on the map. Any curvature. Any direction. Toronto might see one in 2024.
  • At least two solar and two lunar eclipses happen every year, but most of them are not spectacular enough to be called eclipses.
  • The Roche (Rosh) Limit is the radius at which a large body can tear a smaller body apart, due to the effect of tidal forces on the smaller body.
  • The answer to the question, "immovable objects (a=0) vs unstoppable force (v=constant, so a=0)...", is "they are possible only if they pass right through each other".
  • Infrared thermometers are (typically) calibrated for an emissivity of 0.95. If you use one on a material with a lower emissivity, it'll give inaccurate readings. This can be cheaply solved by sticking a piece of electrical tape on the surface, and measuring that.
  • From a photon's perspective, it takes exactly no time to travel from its source to its destination, no matter where the destination is. Even if something is a thousand lightyears away.
  • The speed of gravity waves is the same as the speed of light.
  • On current: "Current is like rope, it can be pulled; but not pushed." - Thread about shocking your own balls with a car battery
  • Ultrasonic welding uses ultrasound to heat up and weld two adjacent pieces of metal together. Microsoft pulled that dick move once.
  • The Sun undergoes spontaneous magnetic reversals every 9–12 years, where it increases in field strength.
  • Pluto's satellite Charon is massive enough to significantly affect pluto's center of orbit.
  • A 5-gram black hole will emit enough hawking radiation to kill everyone around you (450TJ, like a nuclear bomb).
  • "Optical bonding", à la filling the air gap(s) with special glue, makes your screens reflect less.
  • On most bikes, the pedals never move backwards with respect to the ground, except if the lowest gear is chosen, in which case it might be possible.
  • The more alien life we find, the more likely it is for the great filter to be ahead of us, something that destroys all civilisations. Us not finding any alien life means we might have passed the great filter.
  • Why dark mode is less easy to read and causes eye strain long term: eyes are dilated when viewing light text on dark backgrounds, making it hard and taking more energy to focus (think large aperture cameras). Bright text also scatters light, bleeding light onto the dark background. This does not happen on black on white screens. The best contrast for reading is white on dark blue. If you don't stare at your screen for hours, none of this matters.
  • You can make a huge natural snowball only near the belt where the temperature is fluctuating close to 0°C.
  • A solar eclipse looks like a vague dark spot from space.
  • You don't pump air into your own scuba gear because (a) it's hard, and (b) the pump adds oils and lubricants into the air you breathe.
  • The looping time machine episode of Futurama, where Fry et al. travel to the same universe after the universe dies and recreates itself, came from the Big Bounce theory.
  • The sun's diameter is pretty close to 400 times that of the moon's (400.5).
  • Voyager I is analogue. It takes pictures like a fax machine, and sends them back like a radio.
  • In 2015, the definition of a parsec changed from "the distance at which one astronomical unitsubtends an angle of one arcsecond" to "648000/π astronomical units", which is about 3.26 light-years.
  • When a helicopter or quadcopter descends vertically, (according to /u/eaterofdog) the vehicle may lose lift to the phenomenon called "prop wash". However, when researched online, prop wash seems to generate a leftward torque, rather than a downward force.
  • Lightyear to meter conversion is easy, if you know a lightyear is 9.461E15 meters, and then you just approximate it as 1E16 meters.
  • The Earth is a dynamo, so its field strength depends on how aligned the two poles are. If they are not aligned, the field strength is low, and may even be reversed.
  • The moon is the largest natural satellite relative to the planet's size. This is not hard to achieve, considering mercury has no moons, venus has no moons, and Mars has no moons either.
  • An ampere is a coulomb per second. All of them are considered SI units.
  • Non-lead solders exist. They actually just need to have a lower melting point than then metal you are bonding. To solder gold, you use a 14k gold alloy and some flux (in this context, a strong reducing agent that prevents oxidation at the bonding site).
  • Annealing a metal softens it.
  • According to Orders of magnitude (mass), a fruit fly weighs 0.3mg, and a grain of salt is 2.5mg.
  • Primordial black holes are hypothetical black holes that were created within a second after the big bang. They are hypothetical because they are small and hard to see, and the big bang itself is also hypothetical.
  • Stephen Hawking said there is no possibility of God in our universe because "the combined laws of gravity, relativity, quantum physics and a few other rules could explain everything that ever happened or ever will happen in our known universe". He said there is no time before the big bang, and, therefore, no time for a god to exist in. However, as a sidenote: when you start a Sims game, you existed before the sim's universe was created.
  • All they need to do to make a lighter diamond look bigger is to make it flatter.
  • Putting tiny balls inside small speakers dampens the sound and makes the speakers sound bigger than they really are.
  • A generator at no load uses at least the energy required to continue spinning.
  • Capacitive fingerprint scanners don't work when you're dead. Optical/Ultrasound fingerprint scanners do.
  • A meteor caused the Chesapeake Bay impact crater 35 million years ago.
  • A hydraulic ram delivers water to higher ground by screwing around with an air reservoir that acts on valves that close on them. For hydraulic rams to work, they must have a way to depressurise outside the air valve.