What causes the audible electric buzzing sound from high voltage power lines?

from reddit by Nebonit

The sound you’re likely hearing is partial discharge or corona discharge, not the sound of the frequency of the electricity (unless you’re listening to a transformer). It’s the noise that air makes as electricity jumps through it, basically baby lightning, for power companies this is a problem for polymer and oil based insulation (ceramics don’t mind) as it degrades their ability to resist the voltage. You can’t hear this on low voltage since there isn’t enough ‘pressure’ on the electricity, you could however hear the frequency of the electricity in something like a microwave transformer or a electric motor that is stalled. The higher the voltage, more humid and if there is a sharp point can all make it louder, so have a listen to it on a humid night and you might even see it.

from reddit by Manodactyl
Follow up question, why do I hear the insulators buzz when it’s cold and humid (generally at night), but don’t hear them when it’s warm out (during the day)

from reddit by mattskee

At night the relative humidity is usually higher because of the temperature drop, and you may also have some slight condensation on the insulators. The additional water in the air, and possible water on the insulators, reduces how good the insulators insulate so you get more leakage of electrical current making that sound. On a really foggy night I have even seen insulators periodically flash over, which probably clears them of their condensed water and they continue working.

How do birds that dive from the air into the water to catch fish manage to get back up into the air?

from reddit by qgnn

Birds have an organ called the Uropygial gland, which is an excretory gland that produces oil for their feathers. Birds will use their beaks to spread this oil over their feathers.

One benefit of this oil is that it makes the feathers waterproof.

from reddit by SovietWomble

It’s also for this reason that many birds dislike having their feathers touched. They’ve spent ages carefully cleaning, preening and rubbing oils over themselves for water-resistance, scent marking and anti-parasitic properties.

And then we pink mammals come along with our chubby, Cheeto dust covered fingers and want to handle them.

What is the difference between LED, AMOLED, LCD, and Retina Display?

from reddit by MultiFazed
So these are terms that refer to some fundamentally different things. I’ll throw a few other terms in the mix that will hopefully clarify things:

Display Technology
Cathode ray tube (CRT) where an electron beam is used to excite colored phosphors on the inside of a glass screen. You may have heard it referred to as a “tube TV”. This is pretty old stuff, and is the earliest display technology for TVs.

Plasma displays, where a gas inside each pixel is made to glow. This is now pretty outdated, but still way newer than CRTs. It was especially common back when LCD TVs were new, and lower quality than they are today.

LCD (liquid crystal display). This is the most common type of display tech for televisions. There are three different colors of pixels (red, green, and blue) that can be made more or less opaque to let through light being created by a backlight behind the screen. The combinations of red, green, and blue can be used to form millions of different colors.

AMOLED (active matrix organic light emitting diode). Each pixel is made of of individual little lights that don’t need a backlight. This is newer, and is being used in a lot of newer phones, but is still very expensive for large TVs.

Backlight technology
Note that backlights are only needed for LCD displays

Cold cathode. This uses a light similar to the overhead fluorescent lights used in stores and office buildings.

LED. This uses LEDs (light emitting diodes) to provide the backlight. Newer TVs will have hundreds of individual LEDs to provide even lighting and the ability to dim different sections of the screen to provide better contrast.

Other stuff
Retina Display. This is just a fancy Apple buzzword for having lots of pixels that are really tiny, so you can’t see the individual pixels on the screen even when you look pretty closely.

Why does a good pair of headphones/earphones make it feel like the sound is coming from inside the middle of your head?

from reedit by TheRambunctiousFlan

To put it simply, whenever a sound comes out of both the left and right channels at an equal volume, your brain will often trick you into believing that the sound is coming from the midpoint between the two channels, creating what’s known as a Phantom Center. And since the left and right channels are on either sides of your head, your brain will have you believe that the sound is coming from the middle of your head. Here’s a link if you’re interested in a slightly more detailed explanation: https://en.m.wikipedia.org/wiki/Phantom_center

Why do most hard candies just shrink down as you suck on them but peppermints get all porous and full of holes?

fro reddit by nemamook

I can’t find the YouTube video I’m thinking of, but this one (link should start right about the time they’re “whitening” the white part of the candy cane) gives a good fast-forwarded example of the process. Basically, to get the candy to look white, the candy is folded many, many times, trapping tiny air bubbles which makes the candy look white. Then, as you’re sucking on the candy, your saliva dissolves the microbubbles until you have little bubble craters in the candy.

How does the emergency calls only mode work?

from reddit by billythewolf

Your phone is allowed to use any network its physically capable of using for emergency calls, whereas normally it can only use networks you’ve paid to use E.G. signals from a Verizon tower.
EDIT: Looks like I was partially wrong. Quoting /u/psfilmsbob “Every carrier has roaming deals with other carriers who use the same signal, meaning your AT+T phone will work on T-Mobile towers, vice-versa. Same with every major carrier.”

Why does my nose stuff up when I sit, lay down but clears instantly when I stand up?

from reddit by gesichtsbremse

This is just my little theory but it probably has to do with the oxygen supply in your blood.

It’s a little known fact the swelling of the sinuses is actually regulated by the amount of oxygen or the lack thereof in your blood.

I did figure this out during a very nasty cold. I was wondering, why I could temporarily open my nose by doing push-ups. So I dug deeper. The result is that I now can open my nose consciously whenever it is stuffed in under one minute. It’s almost like a super power. Due to my constantly stuffed nose I used to be a mouth breather and also addicted to nasal spray. But not anymore.

All you have to do is to throttle your breath. Exhale completely and then start to breathe shallow and slow. It will feel a little uncomfortable in the beginning. But soon you will feel the same sensation in your nose, you feel when taking a nasal spray and soon after that your nose will open. One needs to exercise this a little, but soon it feels natural. Breathing into a bag should do the same thing, even though I have never tried this.

It all makes sense if you think about it. I was always afraid of what would happen if something would block my mouth, while my nose was stuffed due to a cold. In reality nothing would happen. Before dying from oxygen deficiency your body will make sure that your nose gets unblocked, no matter how bad your cold is.

So when you stand up, the amount of oxygen available at the brain probably drops due to a decreased blood flow (this is also why one sometimes get light headed when standing up) thereby triggering the constriction of your sinuses.

Tldr; read this post if you want to learn how to consciously unblock your nose

Why does blood not stick to human skin like a permanent marker, but will stain things like clothes so bad?

from reddit by despicablenewb


Your skin is fairly smooth, and is waterproof. When you draw on your arm in marker, the ink is carried from the tip to your skin by a solvent, like propyl alcohol, this solvent quickly dries. The solvent isn’t water, so it penetrates more deeply into the keratinized layer of skin. This leaves the ink on the top of your skin, and a little will get INSIDE your skin (I’m talking in microns) this is why when you wash it off, most of it, the stuff on the surface, comes off fairly easily. It isn’t water soluble, so you have to scrub and use soap, but it comes off. Then you always have a little left, the stuff INSIDE the very outside layer. Which you have to scrub hard to get off, you’re mostly just scrubbing off that layer.

For blood, it can’t get inside your skin, so it just dries on the surface. It’s also water soluble, so it’s easier to get off. The color is also from red blood cells, they’re much larger than ink molecules, but the blood just stays in the cracks of your skin that are harder to clean.


Think of a rope, the brown kind you see on ships in movies.

Thread isn’t that much different, just smaller.

Ink will stain the fabric just easily as blood. The solvent spreads the ink into the fabric through capillary action and that’s why when you draw on a white shirt with marker, you get the bleed where you aren’t marking, the ink is traveling down the thread.

Blood interacts with the threads in a similar way. Cotton will absorb water, so blood will absorb onto the thread just like ink. It will go into all the little nooks and crannies of the thread, and while red blood cells are bigger than the ink, they’re small enough to get to the very inside of the thread.

Then you try to wash the blood out, the red blood cells are inside that thread, they’re trapped now, they flow in, but can’t flow out. When you wash it, the red blood cells pop, leaving the red color behind, which is still trapped, stuck to individual cotton fibers now.

That’s why you can wash out some of the blood, it’s the blood on the surface of the thread, but you can’t wash the blood that’s on the inside of the thread.

Edit: I avoided talking about prune fingers because it’s contentious and irrelevant to this ELI5.

Prune fingers are better at grabbing while underwater, but is it due to the absorption of a small amount of water on the exterior surface of your skin? Or is it due to the body increasing the porosity of the capillaries at the skin on your fingers that causes the swelling? It’s currently being investigated and I have yet to see conclusive results from either side.

However, it’s irrelevant for this conversation. If you put your hand in a bowl of water, how long does it take to get prune fingers? How often are you floating your hand in blood?

If I put a droplet of blood on your arm, it will bead up and you can just brush it off. Or, you can take a cloth, and the cloth will absorb the blood.

So for this conversation, skin is waterproof.

Edit 2: a couple people have mentioned that those with nerve damage don’t get prune fingers, which supports skin being waterproof and that prune fingers are from a biological response. I haven’t heard of this before, so I won’t comment on it beyond saying that it’s compelling proof.

That prune fingers is due to absorption of water by the skin was probably not something a scientist tested. It is a completely logical and sound thing for someone to assume, and even if skin is waterproof, that you eventually absorb some water is still reasonable.

These kinds of facts are very common, no one thinks to test them, there really isn’t any reason to, until there is. That prune fingers is due to a biological response could be a very important fact for science, it can help teach us about localized responses, how local conditions are sensed, how the brain analyzes the information, and many other things.

This is why I question everything, if it hasn’t been tested, then it is only a hypothesis, not a fact. Also, not to trust anyone, always read the literature XDl

If all human cells replace themselves every 7 years, why can scars remain on you body your entire life?

from reddit by _the_originalRetro

Human cells can replace themselves, this is correct. But they need a scaffold to replace themselves ON for them to be in the right place. And the nature of that scaffold is why scars stick around forever.

Let’s compare our bodies to a multi-floor brick building that King Kong or Cloverfield or Godzilla or something punches a big chunk out of.

You have a couple choices to do something about that building before the weather gets in and wrecks it worse. But a feasible one of them isn’t a complete tear-down and rebuild using scaffolding and heavy construction to recreate the building properly. People have got to go on living in there and there’s not enough free spending money around to do it.

So you patch that hole as best you can and maybe brick up the opening, and that’s good enough for people to keep living in it. But it leaves a not-very-pretty gap in your building. It’s functional even if some of the electrical stuff or elevators don’t work due to the still missing area, and it looks ugly because you couldn’t quite get everything perfect without bringing in super-expensive heavy machinery and shutting everything down, and the bricks don’t match. So you’re left with a serviceable building with ugly spots that you can’t ever afford to make perfect-looking again.

Scarring’s the same. The body doesn’t have the ability to regenerate huge missing areas because it can’t create scaffolding once you’re out of the womb. All of the ‘heavy equipment’ necessary for it is no longer available. This wasn’t critical enough of a skill for us to evolve as a species because enough of us survived and had kids even without it to take over the world. So the body goes with a “walling off” strategy without coming with a bunch of perfectly set-up scaffolding to build new clean supporting structures for the new cells to grow back into their perfect original shape.

And those wall-offs are dead ‘hard’ tissue that is permanently set into their walled-off shape and can’t be replaced. Again, perfect-looking repairs weren’t necessary to the survival of our species so we didn’t evolve them.

Why is not there a standardized type of fastener?

from reddit by hawkeye18

As usual, there is a relevant XKCD…


Automod appeasement edit:

At one point, there was only one type of screw. I’m no screwolologist, but it seems fair that the straight slot would’ve been that one type.

Its ups were that it was easy to manufacture and it was easy to make a tool for it, but anybody who’s used a straight-head knows it’s a terrible, terrible screw head.

So somebody set out to make a better one. I’ve no idea if I’m right, but I’m gonna guess it was a guy named Phillips. So he said, if one slot was ok, then two slots should be better! But anybody who’s used a Phillips screw knows that they come with an appallingly low torque limit before you now have a conical-head screw that’s impossible to do anything with.

So somebody said straight heads suck, and phillips heads aren’t much better, so I’ll make one with some more meat in the tool and straight sides so rounding off and breaking tips wasn’t such a concern. Thus, the Allen head was born. Except that allen/hex heads, below a certain size, are even easier to round out than Phillips heads were, and it’s fucking impossible to get the hex key in there straight/to full depth in the fastener.

So somebody said, that Allen guy was on the right track, but he didn’t go far enough. So the Torx bit got invented.

But then, people said that Torx was too complicated and it’s impossible to tell the difference between a T25 and a T27 and oh my god why are there so many choices? So we went back to basics and saw if we couldn’t improve on the Phillips design, which beyond its propensity to snap tips and round off fastener heads wasn’t a bad design. So we got stuff like JIS, which is virtually identical to Phillips but designed to destroy your phillips bits, and Posidriv, which is the bane of my personal existence because they’re designed to never, never strip while tightening (which they don’t), but to always always strip immediately when removing (which they do).

So that shit got real complicated and somebody said, guys, guys, you’re making this too complicated, eh? What if we took an Allen, which is ok but has too small a load-bearing shoulder and too-great leverage angles, and simplified it, eh? And the Robertson (us Yanks call it a square bit) drive was born. And it was good.

But somebody saw that the construction industry was using a messy hodgepodge of phillips and robertson screws and said, what if we combine them so construction people don’t have to buy so many different bits? So now there’s a combined R1/#2 phillips bit and screw. I guess that guy never got told about Torx bits, but hey, whatever. So now the construction industry is using an even messier hodgepodge of phillips, robertson, torx, and combi-drive bits.

And then, electronics came along, and at some point electronics manufacturers decided that we lowly consumers couldn’t be trusted/were too dumb to open their electronics, so anti-tamper bits had to be made, because everybody had tools to open the bits that were already around, for the most part. So they made those, starting with the Torx bits with the little posts in the middle, but it turns out those are pretty expensive to manufacture so they started making tri-wing screws, and those dove-tail head screws and the two-post screws and etc. etc. etc. because all the same shit that happened in the 10 paragraphs above happened in the anti-tamper-bit world all over again.

Over time each industry sort of settled on certain screw type heads for certain applications, because as there was no “perfect” screw head each type had its strengths and weaknesses, and everybody is firmly entrenched in their own screw head system, and there is very little hope of ever unifying everybody, because there’s a lot of money in it now. That doesn’t stop people from trying, though - but since they don’t understand the market dynamics and why there will never be such a thing as the one true screw head, all they do is just add yet another type to the mix, confusing everybody just that much more.

Edit 2: well now my inbox is screwed, and it seems somebody has put an idea for a new screw head next to my name.