Explainlikeimfive explainlikeimfive

ELI5: What happens to the newly "dead" bacteria on your hands after you use hand sanitizer that "kills" bacteria?

ELI5: What happens to the newly "dead" bacteria on your hands after you use hand sanitizer that "kills" bacteria?

Like another poster has said, you can't really wash off the dead bacteria because water acts differently on them due to their size.

Also when you use antibacterials, the area will quickly become repopulated with bacteria from your environment, other parts of your skin and by the bacteria that wasn't killed multiplying.

As the area becomes repopulated, the new bacteria will use the dead bacteria as a food source. In essence, the dead bacteria becomes food for the still living bacteria.

Edit: words - silly phone predictive text.

So i had to remove the top reply in this thread. I know people are going to want to know why, and my explanation is buried there.

It was a copy and paste of this comment by /u/TheTimeNotTheMiles. That is one of the reasons that the OP of the removed comment didn't respond to anyone.

That violates our rule #3 explicitly. I think though that it violates the spirit of rule #1 as well.

I'll post the contents of that original comment here for convenience.

So lets say we have a scalpel, right? Simplest medical device there is. There's a number of ways to make it totally(ish) sterile- gases, steam, dry heat, gamma radiation.

But as you ask- the little bacterial corpses are still there. Waiting, one presumes, for tiny necromancers.

The problem occurs when you stab someone with the scalpel, preferably in a medicinal way. The bodies immune system works by identifying certain chemical triggers in bacteria, and has no way to know that, for example, the lipopolysaccharide hanging around in someone's heart is not part of a bunch of living bacteria, but the floating corpses of dead bacteria.

The dead byproducts of bacteria are called "pyrogens" because they cause (among other things, such as death) fevers.

Where do they go? Nowhere. Bacteria are small enough that water has completely different properties on their level. Beyond rinsing off gross matter and reducing bacterial load, washing can't do much.

So for things like heart surgery scalpels, there will usually be a second step of "Depyrogenation" This is the process, not of killing bacteria, but of removing the bits left behind so they don't trigger an immune reaction. This varies widely in complexity depending on what you have to depyrogenate- steel scalpels are easier than an injectable drug, for example. Typically, the goal of the process is to so thoroughly break down the biological material left behind.

Are my hands covered in bits of dead bacteria?

No your hands aren't covered in dead bits of bacteria. They're covered in happy, healthy bacteria.

Then why wash my hands??

Washing your hands removes dirt and debris that carry the nastiest bacteria. Sterilizing your hands is a ridiculous notion however- your hands are made of cells, bacteria are made of cells. Anything that would kill them would kill your cells. Your hands, and literally everything else on the world not currently under direct gamma radiation bombardment, are covered in bacteria,

Quick run down on terms:

"Cleaning" a medical device is basically doing dishes-getting blood n bits off the reusable ones. (plz dont reuse single use medical devices that makes regulatory professionals sad 😭)

"Disinfecting" is using chemicals to get something purty darn clean.

"Sterilization" is killing all* the germs on something

"Depyrogenate" is taking bacterial corpses and reducing their remaining structure to a point where your immune system won't recognize it and freak out.

*SALx10-6 is the typical sterility level for a medical device. one in a million germs/one in a million devices

Edit: I'm going to unsticky this as i think this and my original removal reply are visible enough on their own by now.

I'd prefer not to have bacteria corpses on my hands, thanks.

The irony here is that the human body contains just as much bacteria as our own cells. Not only that, but we are desperately dependent upon the bacteria that lives on our skin to protect us from all sorts of nastiness.

Stealing someone's work? No one is making a profit off comments. Lazy? It's Reddit, we're not writing peer reviewed journals.

I'm so tired of sifting through deleted comments. And it's sad so often the top comment is deleted. That shows there's a real problem going on. I totally get the importants of moderators on reddit, especially since there's so many subreddits. But everyday there's new rules, new interpretations of rules, and more moderators who feel like they have to delete comments and lock posts to validate themselves.

I cannot stress this enough so I'll say it again, it's just reddit. No one is making a career off comments. Just let people have a discussion.

ELI5: Whem pouring liquid from one container to another (bowl, cup), why is it that sometimes it pours gloriously without any spills but sometimes the liquid decides to fucking run down the side of the container im pouring from and make a mess all around the surface?

ELI5: Whem pouring liquid from one container to another (bowl, cup), why is it that sometimes it pours gloriously without any spills but sometimes the liquid decides to fucking run down the side of the container im pouring from and make a mess all around the surface?

Might not have articulated it best, but I'm sure everyone has experienced this enough to know what I'm trying to describe.

Surface tension. Water wants to stick to hard surfaces. This is what causes a meniscus in a test tube, for example. That "u" shape at the top of the water. The attraction between the surface and the water molecules is stronger than the attraction of the water molecules to each other.

So, when pouring, the force of the gravity on the water needs to overcome this surface tension to pull the water away from the container. When the angle between glass wall and vertical direction is small, the component of gravity perpendicular to container wall is small and surface tension is stronger, causing the water to stick to the container and run down the outside.

I appreciate all replies but yours is what I was mostly looking for! Thanks for the detailed reply.

An extra tip is to make sure there is no liquid already running down the side of the glass! Once there is a path of liquid for the contents to follow it is much more likely to have dribbles from the side. I have tiny refill glasses to use at work and once I've made a spill it gets even messier. If I wipe the side of the glass off there is less of an opportunity for the liquid to hold onto the glass.

Fuck, you just made me realize why it's called a beaker. I feel dumb.

ELI5: what is the reason that almost every video game today has removed the ability for split screen, including ones that got famous and popular from having split screen?

ELI5: what is the reason that almost every video game today has removed the ability for split screen, including ones that got famous and popular from having split screen?

3 Main reasons:

It takes a lot of extra processing power to generate the split screen aspect.

Its development work they would rather put towards their more lucrative multiplayer (usually with microtransactions)

they sell more copies of the games to groups of friends who want to play it.

Now all of those are horseshit reasons, and I want my couch coop back, but still. I would (and do) support games with couch coop, like borderlands, lovers in a dangerous spacetime, speedrunners, etc. I recommend you do the same.

Also fuck Halo 5.

What I gather is that most people don't have siblings and thus the concept of "if it's not split screen we can't play together" doesn't get across. And maybe I have rose tinted glasses but it feels like games like halo reach or some of the older cod's had good graphics and split screen, and I mean we all know how fast cod pumps out games so it's not like they sacrificed getting the game out on time to allow my brother and I to get top of the leaderboards on cod zombies

Edit: I meant most people commenting don't live with siblings currently or don't have any. I in no way mean that most people are single children. My comment was poorly worded. My bad

Yeah seriously. And as I've commented, they're missing the family demographic. I have brothers and so we used to go out of our way to only buy games we could play together. Now if we did that we just couldn't buy any games, and thus we don't buy as many

The core of it is that it takes at least twice the computing power to render two separate viewpoints, and simulate the physics, AI, etc for those separate viewpoints. Additionally, it takes extra memory and invalidates some "hacks" that work when you only have one viewpoint. This means that it's a lot more work to render two viewpoints than it is to render just one. It's a lot of work for graphics programmers. They have to:

Remove hacks while maintaining framerate Find the memory to render multiple viewpoints Figure out how to swap to cheaper assets and rendering techniques Figure out how to render split-screen with whatever new, cutting-edge PBR/HDR/deferred techniques your game is running, and make it work on whatever potato Marketing has decided your min-spec is.

It's a lot of work for gameplay programmers. They have to:

Remove hacks while maintaining framerate Help designers with AI issues. Things like an aggro system and limiters for AI numbers Help designers with scripting issues

It's a lot of work for artists. They have to:

Build cheaper versions of the assets. Generally this is done already when they author LODs, but they have to make sure the LODs hold up close to the player This step applies to nearly everything in the game - meshes, textures, explosions, etc... Optimize the game for double-rendering. This means going through the game and tagging things to not show up at all in split-screen. This part is crazy time-consuming.

It's a lot of work for designers. They have to:

Make sure AI works with two+ player characters. Make sure scripting works with two+ characters. What happens when one guy runs ahead and triggers a cutscene, for example? Make sure pickups and items read well in smaller windows.

All of this while Marketing is complaining that the game looks worse in splitscreen and Production is changing the end goal and redefining what "game" means.

Once all this work is done, Marketing looks at the numbers of people playing splitscreen and decides it's not worth doing all this work on the next game. Source: Shipped a split-screen game.

Edit: Obligatory "Thanks for the Gold, stranger!"


ELI5: Why is the ozone layer higher up than oxygen gas? Should not ozone(O3) weigh more than oxygen gas(O2) and therefore closer to the earth?

ELI5: Why is the ozone layer higher up than oxygen gas? Should not ozone(O3) weigh more than oxygen gas(O2) and therefore closer to the earth?

Ozone is found lower down in the atmosphere as well. You can even smell it. It is what produces the smell of lightning or other electric sparks. However ozone is very reactive and will quickly react with other elements. So even though ozone is heavier then oxygen you will usually not find it far from where it is being created. The reason there is a layer of ozone in the upper atmosphere is because oxygen will react with ultraviolet light to create ozone. And the upper atmosphere gets a lot of ultraviolet light from the Sun.

The ozone isn't a permanent layer that has 'risen' higher than the oxygen. Ozone only 'lives' for about an hour, but it is constantly being replenished by the interaction of UV rays from the sun and atmospheric oxygen. A photon of UV hits an O2 molecule and splits it in half, leaving two free oxygen atoms floating around. These readily bind with whole O2 molecules, creating O3. This absorption of UV is what makes the O3 layer so important.

EDIT: I worded the last part poorly. Ozone itself is very good at absorbing high energy UV. Oxygen is good at absorbing lower energy UV. The photodisassociation of the oxygen is not part of the absorption process.

Others have already replied to your question, but this is an important detail: even if a molecule is heavier than another per se, it doesn't mean the actual material composed by those molecules will have a higher density. H2O is a tiny molecule but water has a higher density than a vast majority of organic compounds like diethyl ether, methylamine, ethyl acetate... it all depends on the packing of the molecules.

Edit: on the other hand, with gases, you can guess their relative density by looking at the molecular weight.

Gonna be quoting this site.

It's not that there isn't ozone near ground level because you're right it has a higher density. It's that ozone is typically formed in the upper levels of the atomsphere due to O2 reacting with free radicals of oxygen which are generally formed from the solar radiation that is constantly shining on Earth.

ELI5: How do new houses hook up to existing sewage and water lines without disrupting service or spewing liquids?

ELI5: How do new houses hook up to existing sewage and water lines without disrupting service or spewing liquids?

Residential sewer is pretty much all gravity main (a pipe that relies on gravity to take wastewater to a larger gravity system that might join several neighborhoods and in most cases ends up at a pump station). You can trench to the main and tie in by drilling a hole and fitting a saddle while still in operation.

Water service is largely the same process but done under pressure. The process is called hot tapping a main. A special drill rig is used that fits through a saddle and valve. The residual pressure from the pipe pushes out any debris generated by the drilling process and (ideally) the line would be flushed at the end of line blowoff after drilling to ensure that this is true. Demo here:

Engineer working in the drinking water industry here.

The answer to water and sewer are separate.

Water: "Tapping" machines insert a new valve (typically 3/4"-1" diameter for residential) into an existing water main while it's live, and the valve is installed in such a way that it is closed when the installation machine is removed, so water doesn't go everywhere. The new valve threads right into the existing water main, which is typically made of iron, though there are other materials (plastic, concrete) used throughout the country. These machines also exist for larger buildings, which sometimes require 4-8" connections for domestic water and sprinkler systems, but this process is much more expensive when you get to these sizes. In both cases, since the valves are installed closed, the contractor can then run the water pipe into the building and connect to the plumbing, then only when everything is hooked up open the new valve.

Sewer: Sewer mains are generally gravity flow, and are not full. As a result, you can often cut a hole in the top 3/4 of the pipe, install a new pipe to form a T or Y, and then seal up the hole without too much mess.

Sewer and water guy here. Finally a question I can answer! Sewer mains are gravity operated, so you can cut a hole into the top of the pipe and no liquid will escape. Sewer mains are made of various materials, from plastic to clay to concrete, but all are tapped the same way. We usually dig down to expose the main, and cut a hole in it using a cordless drill and a 4" diameter hole saw. Then a rubber boot is placed on the main, and fastened using metal bands that wrap around and tighten with a screwdriver bit. We coat the pipe and the rubber boot with a type of cement to prevent roots penetrating into the pipe and causing blockages. The boot has a mouth on it that accepts a new 4" plastic line that runs to the new house. It's inserted into the boot, and tightened using the same style metal band clamps.

Water mains are a different process. It really depends on the material the main is made from. For cast iron of ductile iron mains, we have a "tapping machine" that drills a hole and inserts a new tap while the main is still under pressure. The device is made of brass. We place a rubber ring on the pipe, and sit the machine on it. A chain wraps around the pipe and connects to both sides of the device. We tighten two nuts to put tension on the chain. They have to be pretty tight so the rubber ring compresses enough against the wall of the pipe to prevent water from blowing out under pressure. The device is a long tube with a flap halfway down inside, that can be opened or closed with a lever on the outside. The cap that fits on the end of the tube has a metal shaft on it that accepts a special drill bit. The bit drills a hole, then cuts threads in the hole so it will accept the new tap. The cap/shaft/drill bit assembly is slid into the shaft and tightened into place. The shaft can be slid in and out without removing the cap. A large drill is attached to the end of the shaft, and the tapping process begins. The drill is geared very low. It doesn't spin fast, but has a lot of power. The tapping device has an arm that flips up and turns slowly with the drill shaft. The arm applies downward force so the bit cuts faster. Once the new hole is drilled and tapped, the drill is removed and a ratchet wrench is placed on the shaft to back the bit out by hand. The tapping device arm is still holding the shaft, because without it, once the bit is backed out of the threads, the water pressure will force the shaft out with an extreme amount of force that could possibly impale or otherwise seriously injure the man holding it. Once the bit is screwed out, the tapping device's arm is removed and the shaft is pulled out as far as it can go. This is where the flap inside the tube comes in handy. With the shaft retracted, you pull the lever to close the flap, and release the pressure from the end of the tube. The water pressure holds the flap closed, allowing us to remove the cap/shaft assembly. We remove the drill bit from the end of the shaft, and replace it with the new shutoff. The shutoff is a brass fitting that has one end threaded so it screws into the pipe wall, and is made to accept a piece of pipe in the other end. The water can be shutoff by turning a small flat piece on the side with a wrench. A metal cap is screwed onto the shutoff, and it attached to the tapping machine shaft. The shaft/cap assembly is placed back in the tube, and the flap is opened allowing the water to pressurize it again. Once the pressure is equalized, the flap is opened all the way. The shaft is pushed down until the threads of the shutoff touch the hole we drilled and tapped earlier. The shaft is turned with the ratchet wrench until the shutoff is tightened in the hole securely. With the shutoff in the hole, the tapping device can be removed from the pipe. We take a wrench and tighten the shutoff some more if it's too loose or leaking. We attach a pipe to it and connect the other end to the customer's new water meter, completing the new water service.

If the main is plastic, the process is slightly different. Plastic pipe is too thin and weak to screw a tap directly into it. A saddle must be used. A saddle is a metal fitting that has a rubber ring on the surface that mates with the pipe. It has metal clamps that go around the pipe and bolt to the saddle. Once these are tightened in place, a shutoff is threaded into the saddle. The shutoff is turned to the "open" position and a tapping machine similar to the kind used on larger pipes is threaded onto the shutoff. The tapping machine has a shaft with a drill bit on the end inside it. A drill is attached to the end of the shaft, and a hole is drilled into the plastic pipe, inside the saddle. Once a hole is drilled, the shaft is retracted, and the shutoff is turned to the closed position. The tapping machine is removed from the shutoff, and a pipe is attached and ran to the new meter.

These methods of tapping a pipe "hot" allow new services to be added without shutting down the main at all.

/u/toddlikesbikes has service lines covered, but I figured I might as well mention how water and sewer main construction is done.

When water mains are rebuilt, there's really no choice but to shut down the main since they are pressurized unless you are hot tapping as has already been mentioned (you can do it with big mains too). That doesn't mean that everybody serviced by the main will go without water for the duration of construction though. For a planned, lengthy shutdown of a main, the construction crew will run temporary water lines to each house. These smaller lines (usually just 2-4" PVC) are hooked up to a fire hydrant outside the work area, and ran above ground through the yards of the homes. Then, a hose is hooked up to the house somewhere, usually the garden hose spigot on the exterior of the home, and the main water supply valve is closed. This allows the homes to continue receiving water service as usual.

Sewer mains cannot be "shut off" because they are gravity fed. When a run of sewer main is to be replaced, the crew will go to a manhole upstream of the work and drop a hose into the manhole. Then, they will hook it up to a big trash pump, and run more hose to another manhole downstream of the work. Then, they turn the pump on and dam the outlet of the upstream manhole with sandbags and wait for the main to drain. Since there will usually be sewer services within the project area, flow won't be completely eliminated, but the amount of sewage coming out of just a few houses is negligible.

This isn't what you asked exactly but I thought you might find it interesting as well.

ELI5: If I break my finger or cut it or smash it, it can heal, but if I cut it off it won't grow back. Why? All of those tissues can grow back individually, so why can't they grow back together?

ELI5: If I break my finger or cut it or smash it, it can heal, but if I cut it off it won't grow back. Why? All of those tissues can grow back individually, so why can't they grow back together?

Long story short, your body doesn't know how to read the 'blueprint' of your finger anymore and can't grow a new one. Your genes hold the blueprints, but they require the help of some molecules known as morphogens to actually shape your body. This happens during embrionic development. Morphogens either cause or prevent certain types of growth in certain parts of your body, causing it to become the shape you are familiar with.

Now, this is all fine and dandy if you are an embryo, but imagine if we had these morphogens in our bodies active as an adult. We would be continuously growing random parts of our body. This is actually one of the pathways that cause cancer. Cancer is bad, therefore our bodies suppress these morphogens after we don't need them. The problem with this is that while we still have a blueprint (genes), we fired the architect (morphogens) who know how to read the blueprint. You can patch up holes without a blueprint but you can't build a new balcony if the one you had fell apart.

As for why we can patch up holes, well it depends on the tissue. Scar tissue isn't the same as normal tissue, it's more a mix of collagen just holding everything together. Kinda like pouring concrete. Your bones are always balanced between dissolving and growing to begin with, so more focus on the growing part means two shattered fragments can eventually become one. Kinda like mortar holding two bricks together. This all is directionless and doesn't need a blueprint, so it can be considered DIY. No need for an architect here.

Edit : Wow, this blew up. Went back to sleep after typing this out and came back to this. RIP inbox lol. Thanks for the gold!

Edit 2 : since a lot of people are asking, let me explain a little about why i think therapeutic application of morphogens isn't exactly viable. Please note that i am not an expert on this subject and i'm just trying to keep things simple.

If you've ever done origami, or paper-folding craft, you'll know that the paper needs to be folded in a specific order. If you try to do it out of order, a corner you need to fold won't be there; it doesn't exist yet. Morphogens are similar to each individual step of folding the paper. As you need a specific corner of paper to fold, morphogens require a specific type of cell in a specific layout to interact with. Because the starting point is different in an embryo and in an adult, the results will also likely be different. And different can mean bad things.

For the most part their lives arent long enough for it to be a problem, and they tend to be simpler evolutionarily, so there's less to go wrong.

Do animals that can regenerate limbs/appendages have increased/-ing rates of cancer?

simpler evolutionarily

Edit, since I'm rustling some jimmies:

Evolution does not strive for complexity. Some of the most evolutionarily successful organisms are simpler in genotype and phenotype, take bacteria for example, simple genome, not evolutionarily simpler. Evolution does not have a direction or a predefined goal. Many plants have more complex genomes than our own.

ELI5: How do trains make turns if their wheels spin at the same speed on both sides?

ELI5: How do trains make turns if their wheels spin at the same speed on both sides?

Train wheels are actually conical. So, when a train turns, it slides to the larger part of the cone on the outside wheel and the smaller part on the inside wheel. That way the wheels still turn at the same rate, but their radii are different.

As others have stated, some trains have a conical shape to the wheels that lets them rotate at different speeds. Others don't, and the wheels slide/slip creating a deafening screeching sound. It's especially loud when the train is travelling uphill and needs to exert a lot of force on the wheels.

Source: am locomotive engineer

Holy cow I had no idea. Is that standardized in anyway, or is there a minimum turn radius agreed upon or something?

Both, the comical shape also helps auto correct the train for any deviation on the track. If it for any reason slides to one side, the larger radius of that sides wheels "turn" the train back into center.

ELI5: How does electrical equipment ground itself out on the ISS? Wouldn't the chassis just keep storing energy until it arced and caused a big problem?

ELI5: How does electrical equipment ground itself out on the ISS? Wouldn't the chassis just keep storing energy until it arced and caused a big problem?

Edit: the lead hardware engineer for the ISS, /u/kamiraa, has explained how the ISS achieves a safe voltage potential in great detail here. Shout out to /u/kamiraa for making my week!

I really didn't expect much from this question, but after reading all your responses --every last one-- I want to thank everyone for their thoughtful contributions. Even that one /sub/flatearth guy who asked if I've ever actually "seen" space.

I got this guys :) I used to be a lead hardware engineer for the ISS Electrical Power System. http://imgur.com/a/SUbSU

If you guys have any detailed questions feel free to ask me here (suggested by a user)


This is my first Reddit post , someone forwarded this to me.

Ok . . . . so quick answer we have a SPG (Single Point Ground in the whole vehicle).

The ISS is an interesting vehicle, we have 8 power channels, each with their own solar panels which is on primary power (160V DC), these primary channels get stepped down further to a very fine regulated secondary power 124.5V DC.

Let's explore a single power channel. The primary power is regulated by SSUs (Sequential Shunt Units), we basically turn on or off individual strings to from a single power channels solar array until we regulate very fine at 160VDC. There are 1 for each power channel on ISS (8).

Downstream of this ORU (On Orbit Replacement Unit) is a DCSU (Direct Current Switching Unit) , this DCSU acts as a giant circuit breaker and an availability to cross strap channels during emergencies and maintenance. There are 1 for each power channel on ISS (8).

But . . . because the ISS is constantly going through solar events and the arrays are getting shaded we have a battery backup that "Kicks In" to regulate the 160Volts when the solar panels can't do it alone. These BCDU (Battery Charge Discharge Units) charge when excess energy is available and discharge when needed. There are a 3 PER power channel on ISS (24 in total) and multiple batteries that are used in these banks (the number depends if we are using new li-ion or older style batteries). These BCDUs attempt to regulate at at a lower voltage than the SSU. Because everything flows through these BCDUs (they are always charging or discharging) the batteries contain the positive and negative.

Downstream further is the MBSU (Main Bus Switching Unit), this is the unit that ties all the BCDUs and DDCUs together (explaining next).

Downstream further is the DDCUs (DC to DC Converter Units). These units will buck or boost voltage up or down to regulate 124.5V DC.

You can NEVER tie two power channels together. You would have converters fighting eachother trying to keep up with regulation. They must always be isolated. But there is a common SPG (Single Point Ground) in the center of the vehicle at the Z1 Truss. Ok so the interesting question. The vehicle can travel in different orientations depending on what the operations of the vehicle are. Because of this as the solar arrays are adding drag to the vehicle or collecting electrons you are building a voltage potential at different points of the vehicle. A concern early on became well what happens as the vehicle travels through plasma clouds . . . . if there is a large voltage potential difference between the ISS and this cloud would "Lightning" strike and destroy the vehicles hull. .

The PCU (Plama contactor Unit) was created that is housed near the Z1 truss. These units started out in full 24/7 operation at the beginning of the space station. They take a noble gas (Xenon), inject the excess electrons , and expel them from the vehicle, which keeps the charge of the ISS under control. It was determined at a later date that this lightning event was not credible to destroy the ISS hull, but it was enough to shock an astronaut during an EVA. Because of such we turn these ORUs on during EVA operations (There are 2 per ISS).

Ask questions :) This is fun !!

Ah, something I can answer.

There are two aspects to this question: grounding of equipment with respect to the ISS, and grounding of the ISS with respect to the plasma environment in low earth orbit.

All electrical equipment is chassis-grounded to the space station's metallic structure, which is then bonded to the negative side of the electrical bus at the Main Bus Switching Units, which are located on the center truss segment. These ground paths do not normally carry current, but they will private a return path in the event of a fault. That path will eventually return back to the solar arrays.

With respect to the space environment, the ISS charging is measured using the Floating Potential Measurement Unit to determine the voltage between station and the plasma that surrounds it in orbit. I don't recall what normal readings are, but if it gets too high, or if they are doing an EVA for which the plasma potential is a problem (don't want to shock the crew members!), there is a device called the Plasma Contactor Unit, which emits a stream of ionized xenon gas to "bond" station structure to the plasma environment.

I think you just described a weapon there at the end.

So the frame is surely a common "ground".

However, it can still build up an absolute charge. It's not readily observable by most meters and won't make current flow. But it can have unexpected effects, as observed in an electrostatic voltmeter with the 2 gold-foil leaves which repel each other when touching a DC charged conductor.

I suppose you could build a high voltage DC generator and end it in a negatively charged needle to shed negative charge. But will that even work in a vacuum? And is there any way to shed a positive charge? Well, I suppose you could use a DC generator to charge some sort of mass and then eject the charged mass, but that seems wasteful and creates space-junk hazards.

ELI5: Why do the effects of coffee sometimes provide the background energy desired and other times seemingly does little more than increase the rate of your heart beat?

ELI5: Why do the effects of coffee sometimes provide the background energy desired and other times seemingly does little more than increase the rate of your heart beat?

Caffeine as a molecule blocks the normal activity of receptors in the brain. These receptors usually interact to a molecule called adenosine. When these receptors bond with adenosine, your brain reads this as being tired. If you drink coffee when your adenosine levels are low (optimal time for a cuppa in the morning is 30mins-1 hour after waking up, NOT IMMEDIATELY) then the caffeine blocks these molecules from being bonded with and your brain doesn't feel tired. Whereas, if your brain is all full up of adenosine, then as it can't shove the adenosine out of its place, all you feel are the other affects of caffeine such as increased heart beat

Caffeine does not provide energy at all. It just stops your brain from telling the rest of your body to become tired.

An ELI5 explanation of how caffeine works is probably like this: In your brain, there are keys and keyholes. When the key goes into the hole, your brain performs various functions. There is a keyhole, that when a certain key goes inside, your brain releases chemicals to make you tired. Caffeine fits in the keyhole, but does not pass the message to become tired. It just blocks the real keys from going inside.

In response, your brain makes more keyholes. This is why heavy caffeine users need more and more caffeine just to feel normal. Because you have so many keyholes, if you don't fill them with caffeine, your brain will send super strong signals to make you tired.

The caffeine blocks you from getting more tired. If you are already tired, it can't work.

Hopefully someone will have the full details as I can't remember the names of the chemicals/receptors/etc

Imagine a slot in your brain that only takes a certain shaped chemical. That chemical is called adenosine and it makes you feel tired when it fits into that slot. Caffeine works because it looks similar enough to your brain to fit into the adenosine slot, but because it's slightly different it kind of "blocks" the slot so no more adenosine can be absorbed.

Therefore caffeine doesn't really give you energy at all, but instead it makes you less capable of feeling tired.

By now you're wondering "So why do I feel a pick-me-up from drinking caffeine?" and mindblowing truth is that you weren't tired from adenosine being absorbed, you were tired because you were in the midst of a caffeine withdrawal and thus felt much better once you got your fix.

Caffeine is a beautiful lie.

ELI5 how font designers can design for Japanese and Chinese, languages that both use millions of individual Chinese characters?

ELI5 how font designers can design for Japanese and Chinese, languages that both use millions of individual Chinese characters?

edit: I guess I had overestimated how many characters these languages use -- as many pointed out, it's only tens of thousands, at the most. Thanks for the great responses, though!

It's a lot of work. In fact, Japanese and Chinese font files (ex ttf) are about 30 to 40 MB. Compare with an English font file which is about 0.5 MB.

CJK Type designer here.

1) Limited character set As others have indicated, thankfully no one has to actually design millions of characters. Actual glyph coverage depends on the needs of the font. Let's look at Microsoft as a sample (including Latin & other symbol characters).

Chinese (Trad / Simplified): 30,000 characters. Japanese: 24,000 characters Korean: 21,000 characters

Now, the above includes a lot of glyphs that most people probably don't need. In the case of Korean, the most basic fonts can have just around 3,000 characters (just Hangul and Latin, no Hanja) and work for most scenarios. For Japanese, there’s 48 Katakana, 48 Hiragana, and about 3000 core Kanji (for literacy), which would cover a majority of scenarios. But for a company like Microsoft, a greater degree of support is necessary.

2) Accelerated and Semi-accelerated tools In the case of Korean typefaces, there are tools that help expedite the development of Hangul characters. As Korean syllable glyphs are divided up into component pieces, one can instruct the tool on where to place those components and which variant of each component to use. For some fonts there are 40+ variants of each component! With this sort of tool, building can be faster. But it won't always work for a given situation and then the work has to be done by hand.

In some Japanese foundries, there is something of an ‘toolkit’ that is used with examples of the different kinds of strokes necessary for Kanji. So the digitizer (more on that later) can just drag in the one that is appropriate for a given glyph. However, as each glyph is different, there’s still quite a bit of manual tweaking necessary from there.

Part of the problem with Japanese and Chinese is, like with Korean, there’s significant manual adjustment of a given radical or stroke for every character. So even if a tool was able to at least ‘assemble’ the pieces into a given glyph, you’d have to make significant manual adjustments from there.

3) It takes an army I heard a story from a friend of mine who visited a Chinese foundry. Designers would pull a Hanzi from a hat and that would be the character they have to produce. With an army of 30 people working on a single font, they’d churn through the characters until the font was complete.

In one major Japanese foundry, there is a division of labor—“designers” draw the characters on paper, “digitizers” trace those drawings to digital representation, “production” takes the digital representations and produces actual fonts. All told, it is a significant operation involving a large group of people. It takes them a year to complete a single weight (say, the “Regular”) of a brand new font family.

Producing these things is a TON OF WORK.

A quick aside about Korean—given the existence of accelerated tools for production, these can be done faster than Japanese or Chinese fonts, but the best ones usually have manual edits and tweaking on an extensive number, if not all of the syllables. One Korean type designer I spoke to warned me about the use of accelerated tools—that the actual results from it are not that great. He, obviously, recommended doing everything by hand.


1) It may not be as many characters as you think it is 2) There are some tools for accelerating work, though a lot is still manual 3) Usually the work is done by a group of people, over a period of time, rather than by an individual.

Got more questions? Feel free to ask!

There aren't millions of characters. To quote a BBC article:

Altogether there are over 50,000 characters, though a comprehensive modern dictionary will rarely list over 20,000 in use. An educated Chinese person will know about 8,000 characters, but you will only need about 2-3,000 to be able to read a newspaper.

I am Korean. While you asked for Japanese and Chinese, Korean fonts also requires Chinese characters and thus have similar problem with these languages. Usually, characters for these 3 languages are packed into one font, called CJK fonts.

First of all: do you know what fonts look like?: A list of characters

To put it simple, each font is a gigantic list of letters. If you input a letter, and there's no matching character in that list, it will not come out right; sometimes a blank will show, sometimes a different, typically weird looking letter will show.

Let's count the number of letters needed!: 50,000

Japanese also uses their own letters, which are around ~50. But they come in both smaller form and bigger form, which doubles the count. Still, the number is somewhat reasonable.

Now for the main show! there are a lot of Chinese characters, as you already know. The problem gets even worse because China, Japan and Korea uses different kind of Chinese letter! Chinese uses the most simplified form (along with their own traditional form), Japanese uses less simplified form, and Korean uses the most complicated form. So you need 3~4 sets of Chinese characters.

And Korean letters are a bit more complicated; the written Korean, Hangul, consist of ~30 components, and you are supposed to combine 2~6 of them into one letter. Which means there can be a lot of letters you can make, if there's no limitations!

That's why font creators came up with a limit of their own. For Korean, they picked ~10,000 the most used letters in Korean, and put only those letters in the font. The same goes to the Chinese letters, although I don't know the number. I suppose you can google "Chinese font character numbers" for more detail.

Let's say there are 10,000 for Korean and 4 set of Chinese character. It ends up with 50,000. Add the Japanese letters and it ends up with 50,100. Whatever, let's go with 50,000.

By the way, that's the reason CJK fonts are way bigger than Alphabet-only fonts. Google is distributing Noto Sans series of fonts. If you're interested, look for Noto Sans English and Noto Sans CJK; and compare their size. CJK fonts are way, way bigger than English fonts.

How the fuck do they design letters?: Divide and Conquer

So, do the font designers design each and every letter in the font? All 50,000?

The simple answer is, yes, they design every single letter in the font.

But there is an easy way.

Did I mention that Korean consist of components? Similar principle goes for Chinese, although they are way crazier than Korean. There is ~10 components in Chinese, but in the most complicated case, Chinese characters are combined of 1~30 components.

But, still, they are made of components. Which means you can set a design standard. Once you make a design standard, you can use them as building blocks for more complicated letters. Like LEGO! When you combine each components into a letter, components might slightly change their shapes. Still, you can make more design standards for them, and use them for the letter.

Even easier way!!: Don't design them at all

There's yet another much easier way to deal with this problem. Buy a cheap font license, and recycle them.

Let's say you're designing a font specifically for Japanese and Japanese only. You don't need 50,000 letters; you only need 100 for Japanese letters and 10,000 for Japanese-Chinese letters. If you give up on the rest you can cut off 80% of the work! And that's how it's typically done. There are a lot of Chinese-only, Japanese-only or Korean-only fonts.

Try one of these subthreads