ELI5: How did the modern playground came to be? When did a swing set, a slide, a seesaw and so on become the standard?
On mobile a a coffee shop, so forgive any formatting issues. I studied sports and recreational management at school and had a few courses specifically on playground development and history.
In short, playgrounds are all developed for specific ages and the equipment is designed to help develop physical and social attributes. I'll need to go back to my old notes for the exact age breakdowns but basically: very young ages to help build balance and coordination and motor skills, toddler-child age the equipment focuses on building strength in children (monkey bars, see-saws) and social skills (fake climbing walls, swings, etc.). And parks for adults focus on a mix of physical and social (basketball courts, tennis, disc golf, etc).
Slides, see saws and other playground equipment don't have stringent standards besides safety standards (although this is changing more and more as research on safety and play habits increases) but standard playground equipment all have a specific purpose depending on the age, skills, and intent of use for the target demographic. (classic park for children vs basketball & tennis courts for adults vs walking, scenic or gardens for seniors).
More diverse playground equipment is being made to include multiple ages and developmental goals but it's also why in certain areas you can find out dated equipment that appears sketchy or downright dangerous but is always more fun than hyper safe new equipment.
ELI5: Why is heart cancer so rare?
The heart's an organ just like the brain, right?
This is because muscle cells (also called muscle fibers) don't divide, and cancer is most common in cells that divide a lot. Dividing cells are primed for cancer because: 1) a lot of the machinery needed to divide rapidly is already present in the cell so not a lot extra is needed to make it grow uncontrollably into a tumor/cancer 2) the more a cell divides the more chances it has to make errors. DNA replication isn't perfect, and over time these errors can accumulate into dangerous mutations (this is also why cancer is more common in the elderly) This is why we see a lot of cancer in tissues with a high "cellular turnover" rate - skin, liver, colon, etc. Cells that never divide (muscle fibers, neurons) almost never get cancer. Brain cancer is usually caused by a special type of brain cell that can divide (but not signal) call neuroglia, which forms the cancerous "glioma." Bonus biology fact - because muscle cells fibers don't divide, you have the same number your whole life. Arnold Schwarzenegger has the same number of muscle fibers now as he did as a baby, they're just more packed with the good stuff. Source - biochemistry major, medical researcher.
ELI5: Why do we have separation of church and state, but still have people swear on the bible for government events?
Let's clear up some misconceptions. This answer only applies to USA, and my source is that I'm a judicial clerk who has formally been sworn-in to serve the Constitution. I watch people get sworn in every day.
No one in any courtroom or public swearing-in must "swear" on a bible.
How oaths must be administered are usually codified in the revised code of each state (check yours if you're shockingly bored!). Nearly every oath-administration statute specifically holds that one may say "I do affirm" instead of "I do swear" and that you can substitute "this you do as you shall answer under the pains and penalties of perjury" instead of "so help you God." Rarely is there any requirement to swear on anything at all, and never only a bible.
This is codified by law, and gives jurors/witnesses/public officials the choice.
In my personal experience, I've never seen a judge use a bible for swearing in. My judge, who is a religious man, doesn't even ask "so help you God" and asks if they "swear or affirm" by default. Also, nearly every judge takes a simple "I do" instead of the formal "I do affirm." No one swears or affirms on anything - they just raise their right hands.
As far as presidential inagurations are concerned - again there's the choice to do so. George Washington set the tradition by swearing on a bible (and the origin for the legality of a public official doing this is rooted in "tradition"). John Q. Adams, on the other hand, swore on a book of law (as did I).
The more direct and controversial question is: why do we even allow the choice of swearing-in on religious objects or with religious undertones? The Constitutional answer is likely that it's a harmless tradition dating back hundreds of years into our British ancestry and that a neutral option must be provided by law. It's understood that public servants must serve the public (duh), but they don't magically have their religion removed from their bodies when they become a government official. They swear, specifically, to serve the public and swearing on their religious text doesn't change the words of the oath but intensifies the meaning of the oath by staking THEIR IMMORTAL SOUL on serving the public. But really it's just window-dressing formality with enough tradition behind it to sneak under the Constitutional rigors of the Establishment Clause.
ELI5: Why are fire animations, fogs and shadows in video games so demanding for graphic cards?
Imagine your graphics card is a famed renaissance painter named Giancarlo Pasquali Uberti sitting in a room. In this room is a canvas, paint, and a pneumatic messaging tube like they have at bank drive-thrus. Giancarlo also has a brother named Cirino Pasquali Uberti that he works with. Cirino can't paint, but he's great with customers and runs their shop. Cirino's job is to take orders for paintings, then send messages to Giancarlo that tell him what to paint. He can't fit big messages in the tube, though, it's real small, so each message tells Giancarlo how to paint a single object. A message might be like "Paint an apple 50cm from the left edge of the canvas, 20cm from the top". Giancarlo is very fast, but it takes him longer to finish a painting if he has to paint lots of individual things (it wastes time writing a message, sending the message through the tube, opening it up, reading it), or if he has to paint a really big canvas.
Now, Cirino and Giancarlo are pretty smart, and they've figured out some tricks to make paintings go faster. Cirino takes great notes while talking to customers, and knows how far away each object in the painting is supposed to be. This is known as its depth. While Cirino isn't a good painter, he's very organized, so he sorts the messages by depth, closest object to furthest, and throws away any objects that are hidden behind something else. The only messages he sends to Giancarlo are just those objects that will be seen in the painting. This is way faster! Giancaralo knows that it's in order, so he doesn't have to waste time painting things that overlap. Since it takes time to paint an area of the canvas (the bigger the area, the more time), this is very efficient. Giancarlo doesn't have to paint over the same spots on the canvas at all, he just paints every spot once.
Then comes a job to paint a still life with a frosted glass vase in it. Cirino sorts everything, and realizes there's a problem. The glass vase is translucent, you can see through it, so it changes how stuff behind it looks since it isn't totally clear. No amount of sorting can fix this, and he eventually realizes that Giancarlo is going to have to paint over the same spot twice to get the right look (remember, he can only tell Giancarlo to paint one object at a time in his messages). The clever brothers think about this for a while, and come up with an idea.
Their new plan is to work on the same painting twice. First, they do what they usually do, sort all the solid objects front-to-back, and only paint the ones that can be seen. Second, they sort all the see-through objects back-to-front and Giancarlo paints each one in order, still careful not to paint any that would be hidden behind a solid object. Sorting the see-through objects back-to-front makes sure they look right if two see-through objects overlap, like if you're looking at that frosted vase through a stained glass window. It wouldn't look right if they painted the vase in front of the window! The results look great, but it's a lot more work than just painting solid objects.
Now, for just a single vase it's not so bad, but once you have a scene with lots of smoke, fog, shadows, etc, Giancarlo spends a lot of time going over and over and over spots he's already painted to build up these translucent layers. This slows things down, and it's a big reason why your GPU struggles with these sorts of effects.
ELI5: If it takes two days for food to eventually be pooped out, why do some foods make me instantly have to go?
I remembered reading about this a while back ago and had to do some googling to find his answer but /u/jiggity_gee did a pretty good ELI5 on this.
Edit: This is mainly about diarrhea than regular poop.
"So your bowels are like a long train track and your food is like a set of cars on the track. Transit time between Point A, your mouth, and Point B, the chute, is a bit flexible but normally operates on a regularly scheduled basis. When you eat, you put cars on the track and send them to Point B. As these cars go to Point B, they lose passengers (nutrients) at various points in the thin tunnel portion (small intestine). The journey isnt complete and the journey has already altered the shape of the car pretty significantly giving a rusty color. Once in the larger portion of the tunnel, the cars are checked for stray passengers and are hosed down a bit so that transition out of Point B isn't so bad. Sometimes, the train cars park juuust outside the gates of Point B so they can exit at the best time for the operator (toilet). Now, all of this goes fucking nuts when you load a bad set of train cars at Point A. The track sensors located everywhere along the track, detect this alien set of cars and sends a distress call to the Supervisor (your brain). The Supervisor wants to handle the situation without having to phone the Manager (your consciousness) about the craziness on the tracks and also wants to make sure you never know it was on the tracks. It has to make a choice now: send it back to Point A violently and somewhat painfully risking tearing the tracks, or send it to Point B as fast as fuck? Depending on where it's located on the track, it'll choose the best route. Let's use the destination Point B. The Supervisor hits the panic button and puts all the train cars that are on the track (in your body) on overdrive. The tunnels are flooded with water and lubricant to speed all the cars up and get them the hell out of there as quickly as possible. Cars collide with each other, and previously well formed cars are just flooded with water and lubricant that they are just a soggy, shadowy reminder of their former glory state. The Media (pain) hears about the car collisions immediately begins filming live the high speed, flooded train cars out of control. They want to knos how an alien set of train cars were put on the tracks and they want someone to pay for such carelessness. The Manager is just watching the horror unfold on Live TV but cannot do anything to stop it, because the Supervisor was deaf and he had not installed a means of communicating with him after hours in the office. I hope this answers your question. TL;DR when you get diarrhea, everything gets pushed out, one way or another. There are no passing lanes. Source: medical student Edit: Wow, thanks for the gold!!"
ELI5: Why is Judaism considered as a race of people AND a religion while hundreds of other regions do not have a race of people associated with them?
Jewish people have distinguishable physical features, stereotypes, etc to them but many other regions have no such thing. For example there's not really a 'race' of catholic people. This question may also apply to other religions such as Islam.
Judaism is what's called an "ethno-religious group". Thousands of years ago, that was pretty common. If you were Egyptian, you almost certainly also followed the Ancient Egyptian religion. If you were Jewish, you almost certainly also followed the Jewish religion.
This was to the point that it was almost "by definition". The Egyptians didn't expect non-Egyptians to follow the Egyptian religion, and the Jews didn't expect the non-Jews to follow the Jewish religion. There are writings from antiquity talking about how whenever someone traveled to a different place or married into a different tribe/nation, they'd sacrifice to the local gods of the area, not worrying about the ones back home until they got home. During times of war, there would be attempts to lure the other side's god(s) to your side with offers of better sacrifices or whatever.
Again, this was the common state of humanity and its various groups for thousands of years. It was generally assumed that there were many gods of many nations, each set of god(s) looking out for their respective nations. Pantheons were fluid, with gods in different pantheons being identified with each other (oh, you have a thunder god too? It's probably the same guy, you just call him Bob instead of Spencer, next time I sacrifice I'll call out to Bob too...).
Where the Jews and Judaism differed from most others is that they became strict monotheists (there's evidence that at the beginning of the Jewish religion they were more accurately "henotheists", meaning they recognized that other gods existed, but only theirs was the best/most powerful/chief).
(EDIT: Above I originally said that henotheism meant that they felt it was only right to worship one, not that one was the most powerful/chief/best. The correct term for thinking it's right to worship only one is "monolatry", which is a difference that I swear I knew before. Props to u/Zorro_Darksauce for the correction.)
This monotheism gave rise to the idea that non-Jewish gods didn't exist. While they shed polytheism, they didn't shed the nation-god association, meaning that God was their God and while He was also everyone else's God, everyone else had a lesser role in His plan and weren't required to do as much and/or were denied His special favor.
The other way in which Judaism differed from many others is that this dynamic continued until today. The other major examples that I can think of would be Shinto and Hinduism, but there are countless religions of equal pedigree and age around the world that are often lump under the generic "folk religion" tag.
This is contrasted with religions like Christianity and Islam, which were founded as religions not for a particular people, but for all people. As a result, they had an imperative to go out and convert others to their religion that was lacking in the earlier dynamic (and would even have been viewed as kind of silly..."they're not Japanese, why would they practice Shinto?")
ELI5:If I had $10 trillion and wanted to pay off the U.S.'s national debt, whom do i pay?
Bondholders, which means you technically can't pay the debt off early.
When the US borrows money, they hold an auction, in which people give them 10,000 (usually in large multiples of $10,000) for the right to receive a few interest payments per year and $10,000 when the bond matures. These bondholders can be almost anyone (it's likely tough for Cubans to collect) and the bonds can be resold on the secondary markets. The US collectively owes whomever owns the bonds at any given moment (which includes almost everyone via mutual funds that own at least a few bonds).
The US pays its debts because it wishes to maintain it's stellar credit rating (the US has never defaulted on a debt in it's entire history). That means when the US wants to borrow money, nearly everyone in the world is interested in lending money to the US.
ELI5: Why are the worst positions for your joints/muscles the most comfortable?
/u/Gonzotronic has it right.
It comes down to energy and efficiency. Using our muscles takes energy and work. If we're in a position where muscles aren't working, less energy is being used.
Slouching is the best example. You're essentially just relaxing the muscles of your spine and trunk until most of the weight/pressure is being held by ligaments and joints (or leaning on your arm, etc).
It's also why people default to lifting with a bent back. We know the dangers to our lower back in doing this yet it's more energy efficient as it uses less muscle.
The second part of the question - why are these the worst positions? When we're in one position for a long time our tissue undergoes "creep" in the same way silly putty would if we held it in the air and let it fall (although much more slowly). Things slowly stretch out (ligaments, joints) and can cause discomfort as well as trigger our muscles (remember they're meant to take pressure off these tissues) to reflexively tighten to protect the now compressed or stretched ligaments and joints.
ELI5: Why do we talk weirdly to babies?
I studied language acquisition in college.
I just wanted to note that child-directed speech (motherese) is not universal among all human cultures. Some cultures do not use motherese (such as Samoa and Papua New Guinea) and just speak to children the same as they speak to anyone else. I remember studying about one culture (I can't remember which culture it is) that does not even speak to a baby (child) until the baby starts speaking. The babies in that culture learn the language by hearing it, not by being spoken to.
Regardless of whether child-directed speech is used or not, or even if the child is not spoken to at all, children all pretty much learn and progress in their language development in similar steps and at similar ages.
To sum up, we talk weirdly to babies because it is what is normal in our culture, not because it benefits the baby.
ELI5: Why do so many books have two to three blank pages at the start?
Imagine I took a standard piece of paper. I could fold it into 4 pieces, then cut the top and bottom a bit, staple it, and have a small book.
This is called a signature. They can be as small as 4 pages, or much larger. A book is typically made up of several signatures.
The result is, I can take two 4 page signatures and make an 8 page book, but I have no way to make a 9 page book. If I add one page, I have no way to attach it. You can imagine if I stick the page in and just glue the end, it will easily fall out. I might be forced to make it fit in a 7 page book, or maybe print a 12 page book with some blank pages (some print methods can use 2 page signatures).
The short answer is that when making books its usually easiest to make them a certain way, and blank pages may be the result. A children's book might be 30 pages, but the publisher finds that one 32 page signature is the cheapest method of production. So they might add something to the pages, or maybe they leave them blank.