All right, let's establish this up front. We are not here to rag on science teachers. Their jobs are very difficult and they are making the world so much better by doing them. And when science gets blown out of proportion or oversimplified, it's almost never their fault. So, science teachers, we love you. Thank you for your hard work. Now, that said, thanks to misleading articles, oversimplified books, or plain old misunderstandings, sometimes you walk out of elementary school with a few misconceptions about the world. Ones that stick around for the rest of your life. And we've debunked many of these over the years, so, now it's time to lay them out.

Let's start way up in space. The first time you learned about astronauts on the International Space Station, you might have heard that they're weightless because there's no gravity up there. And, from their perspective, they definitely feel weightless, but it's not because there's no gravity. Here's a very old video from Hank with more.

*Cut to Hank - Is there gravity in space?*

We spend our lives stuck to this planet. The best of us can jump an astounding 2 meters off the ground. The record for a land animal is the tiger, with a vertical leap of barely double that. That's some serious force dragging us down into this thing and we don't usually think about it because we're always under its spell our entire lives. Unless, of course, we get to space, because everyone knows that space has no gravity. Except, of course, everyone is wrong. Okay, probably not everyone. In fact, you may have seen a number of YouTube videos that have set you straight on this topic, but if not, let's get down to it.

Space is packed wall-to-wall with gravity. Without gravity, everything would just shoot off in straight lines. There would be no galaxies or solar systems or planets and the universe would be a supremely boring place. So let's talk, real quick, about how gravity works. This equation (F = G m1m2/r^2) was figured out by Sir Isaac Newton, and he used it to do all sorts of awesome stuff. There are three variables in this equation, the mass of two objects, say, the Earth and the moon, and the distance between them. 

There's also a constant, the gravitational constant, which Newton just worked out by observation. So according to this equation, the gravitational force between two objects is dependent upon the mass of both of the objects and the distance between them. The masses are divided by the distance, so as the distance increases, the force decreases.

At 370 kilometers above the Earth, the height of the space station, there is still plenty of gravity. Indeed, without that gravity, it would just fly off into deep space, so it's good that there is gravity. The space station is in orbit, stuck there by the Earth's gravity. The astronauts are not weightless, they are falling. And that sounds weird because they're safe. I mean, relatively, they're not as safe as I am. But they aren't about to crash into the Earth. That's because they are falling at the speed of gravity while moving horizontally enough to continually miss the Earth. Instead of plummeting towards the Earth, they're plummeting around it. That's what we call an orbit. And just like when, in a plane, you don't feel like you're moving 400 miles per hour, the astronauts have already done all of their acceleration and are at a constant speed, so to them, it feels like they're weightless and motionless. Their only frame of reference is inside of the space craft.

The same sensation can be experienced without being in space by getting in a plane and having the plane drop toward the Earth at the same acceleration as gravity. It looks to all the world like you're floating in the plane because the fuselage is your frame of reference. But really, you're crashing toward the Earth at terrible speeds. The plane and everything inside, all the objects and people, everything is falling toward the Earth at the same rate, so the contents of the plane appear to float because gravity is acting on all of the objects equally.

So let's go back to Isaac's equation. No matter what we do to that distance number, no matter how big, how far apart things are, it always exists. That force never goes to zero. That means that every object in the universe is constantly attracting every other object in the universe. So a hypothetical situation for you. There are two things in the universe, nothing else.

Just one planet and you. It doesn't matter how far away you are. If you are sitting there motionless, you're not floating, you are falling. And eventually, you will fall into that planet. It may take longer than the life of the universe, but you will eventually fall into the planet.

*Cut to modern SciShow*
Man, since 2013, SciShow has grown a lot. Now, in your first science classes, you may have started learning about physics. While you probably didn't get too far into the weeds, there's a good chance you at least saw this diagram of an atom. It's a really popular symbol and it would be easy to think that's what atoms look like. It turns out atoms are a lot more complicated than that, but I'll let Olivia explain.

(That is NOT what an atom looks like)

Have you ever looked carefully at the intro to this show? Like, really carefully? If you have, you might have noticed that there's a diagram of an atom with little electrons orbiting the nucleus. But, here's the thing. Atoms don't actually look like that. Over the years, scientists have come up with different atomic models based on what we know about how they work. The atomic model that's in the SciShow intro was one of them and it has a lot of history behind it. But the most accurate atomic models are a little more complicated, because atoms are complicated.

By the start of the 20th century, scientists knew that atoms were made up of negatively-charged electrons plus some sort of positive charge. The tricky part was figuring out how these charges fit together. The running theory was that the electrons were embedded in a positive sphere, which was called the Plum Pudding Model, because it looked like a traditional Christmas pudding. But, that all changed around 1911, when a scientist named Ernest Rutherford, along with his team at Manchester University, published the results of the famous Gold Foil Experiment.

Rutherford and his colleagues fired alpha particles, which are positively charged, at thin gold foil. According to the plum pudding model, the alpha particles should have just passed straight through the foil, because atoms would be mostly empty space with some charges scattered around.

And atoms are mostly empty space, so most of the alpha particles did pass straight through the foil. But to Rutherford's surprise, some alpha particles were deflected, by a lot. He concluded that an atoms positive charge was concentrated in a tiny central nucleus and these nuclei were deflecting alpha particles that bounced off of them. He also predicted that the electrons were orbiting around the nucleus kind of like how planets orbit the sun. That's why this model is sometimes called the planetary model.

Rutherford was right about protons being in the middle with electrons around them. And you'll still see his model used today to explain the very basics of the atom. It's the one in the Scishow intro! But, there was one major problem with the planetary model. It predicted that orbiting electrons would lose energy in the form of radiation, which would make them spiral inward and eventually crash into the nucleus. This implied that all atoms would eventually collapse, but we know that stable atoms do exist, so there had to be something missing. 

Just two years later, in 1913, Danish scientist Niels Bohr proposed an adjustment to the Rutherford model that solved this problem. Bohr's model predicted that electrons orbit at very specific energy levels, which he called orbits. The electrons could only orbit at precisely those levels, and so they couldn't spiral inwards. An electron could switch levels if it absorbed or released some energy, but only specific, discrete levels were allowed, and electrons couldn't go below the lowest level. That explained why stable atoms didn't just collapse. Bohr's model quickly became the most popular model of an atom, and it's often used today to show the basic way that an atom is arranged. But, it still wasn't totally right.

One breakthrough was in 1932, when English Physicist, James Chadmick, discovered that neutrons exist. Neutrons weren't electrically charged, and they helped explain why the nucleus was so heavy. Another breakthrough involved quantum mechanics, and the idea that electrons don't necessarily orbit the nucleus at all. 

In fact, electrons aren't even really in a specific place at any given time. Instead, they're kind of in lots of different places at once within a bigger area. Then, when you actually measure an electron, suddenly it's in one specific spot within that area. It's a weird concept that's very different from the way that we normally experience the world. But, that's quantum mechanics for you.

The area where you might find it if you tried to measure it is called the Electron Cloud. In diagrams, normally the cloud is drawn darker where there's a high probability of the electron being there when you measure it. With the most basic atoms, like Hydrogen and Helium, this cloud looks kind of like a big sphere. And it turns out that electrons have the highest probability of being in one of Bohr's obits, which is why you can use Bohr's model to simplify things. But, when you get into bigger and bigger atoms with more and more electrons, these clouds begin to interfere with each other and start to have weirder shapes.

So, the Electron Cloud model is the most up-to-date model of an atom, and it's used by scientists around the world. But, that doesn't make the other models useless. Like, Bohr's model can be helpful if you need to focus on energy levels and radiation. But, if you're studying chemical bonds, you might need the Electron Cloud model to know where the electrons are. And, if you want a model that shows off the fundamentals and still looks pretty cool, you might want to go for the planetary model. 

*Cut back to modern Scishow*
Now, back in elementary school, there's also a good chance you first learned about the human body in depth. Stuff like how your body makes urine to get rid of waste. And along the way, you might have picked up this idea that urine is sterile. Maybe from some kid on the playground who had been watching survival documentaries with their older siblings. And it's understandable; I mean, it's what people were taught for a long time. But the next time you or one of your friends gets stung by a jellyfish, you should probably hold your bladder. Here's Hank to explain why. 

(Is urine really sterile?) *Cut to Hank* 
For some reason, the TV seems to be full of guidance about what you can do with your pee. Like maybe you're watching one of those wilderness survival shows, and the guy falls down into the ravine 

and gets a big gash on his leg, and he's like, "oh, no worries. I'll just pee on it! A little urine will spruce that right up!" Maybe you're watching Lost, and Hurley steps on a sea urchin or a jellyfish or whatever, and he's like, "Pee on it! Somebody pee on my foot!" I got news for ya. Despite telivision's teachings, and in fact what many doctors and nurses were taught, there's increasing evidence that your urine is not sterile. 

The idea that urine, and by extension your bladder, is free of bacteria stems from the fact that under normal circumstances, it won't produce results in a laboratory culture. But that means if a sample of your urine is added to a growth medium and incubated in the right conditions, it won't produce big, flourishing colonies of bacteria, if you're healthy. Doctors have been using these urine cultures for generations because they're really good at detecting large amounts of certain types of bacteria, like E. coli and Klebsiella that can cause infections in your bladder or urethra. However, if your culture comes back negative, that does not mean there's nothing there. For one thing, the threshold that labs use to diagnose bacterial infection in your urine is kinda high. To get your results, lab technicians count colonies of bacteria and each colony is basically a little speck growing on the growth medium. And if there are fewer than 100,000 colonies growing in a single milliliter of your urine (that's about 1/5th of a teaspoon), they will give that a negative result. They just assume that those germs were picked up on the way out of your body, or simply aren't statistically significant, and they want to avoid reporting a false positive. But even the bacteria that show up in these cultures are only the ones we can test for.

The fact is, there is only a small percentage of bacteria that can actually be cultured in labs. There are entire genera of bacteria -- thriving out there in nature, eating and being eaten, recycling elements, and basically making the world work -- that we don't know how to grow in Petri dishes.

And it's also worth considering that you're literally teeming with bacteria right now. I'm talking on the order of trillions of microorganisms, inside and out, forming what scientists call your "human microbiome" -- basically the habitat your body provides for lots and lots of tiny livestock.

And recent research has shown that your bladder is part of it. Several studies in the past few years have found lots of unculturable bacteria swimming around in the urine of otherwise healthy people. And they found them, not by using the old Petri dish technique, but by scanning the pee for tiny sequences of DNA, specifically telltale genetic markers that we use to identify and classify bacteria.

In one study, urine was sampled from two groups of women: one who had some symptoms of urinary infections, and another healthy control group. All of the women had already tested negative for bacteria by conventional means, but 91% of them turned out to have bacteria living in their pee, including some kinds that cause infections.

In a separate experiment, similar techniques were used to compare the urine of healthy women with that of women who had overactive bladder syndrome: a condition that makes patients feel like they have to pee frequently, even when their bladders aren't full. The results showed that both groups had ample bacteria growing in their urine, but the populations in the women with overactive bladders were different than those of the control group, suggesting that the syndrome might be microbially caused.

In the end, the researchers say your urine may well have some bacteria in it that are causing problems, they're just hard to detect. But it's even more likely that it contains bacteria that pose no danger, and who knows? Some of them might even be beneficial.

So next time you pass your pee test at the doctor's office, keep in mind that that doesn't mean your pee is sterile, so don't do anything crazy with it. And if you happen to skin your knee while you're out in the woods, wash it with soap and water... not with pee.

[switch presenters]
Okay, next up: animals. Because if there's anything kids love learning about, it's animals. Especially their pets! If you had a dog when you were a kid, or even if you didn't, somebody probably told you that dogs can't see color. Maybe in a show-and-tell presentation, or in some program about animal biology. And you can probably guess where I'm going with this: there is a little truth to that idea, but it's still not quite right. Here's Michael with more:

Text: Can dogs see color?

[switch presenters]
Maybe you've heard that dogs can only see in black and white. 

It's one of those fun factoids that people like to toss around sometimes. But this, like so many things we talk about on Quick Questions, is a misconception. And the misconception stems from the fact that dogs are, from a human perspective, colorblind. But that doesn't mean they can't see color.

We perceive color through a series of receptors in the retinas of our eyes called cones, and humans have three kinds, each of which is activated by a specific wavelength of light, corresponding to a certain set of colors. Most humans have cones that can detect blue, green, and red wavelengths of light, but dogs, kind of like humans who are colorblind, only have two kinds of cones that work.

For dogs, the two colors they can register are blue and yellow. So dogs can't see the color red, but they can see and distinguish between various shades of yellow, blue, gray, and something that probably comes through as a "dirty greenish brown". So while we see this [Human Vision diagram], your dog sees something more like this [Dog Vision diagram on right]. It's not exactly Technicolor, but it's a lot more information than just black and white. And, setting the record straight about dogs' partial color vision is teaching us a lot about how pups experience the world.

Recent experiments have found that dogs who are trained to find dark yellow objects could still find them even if they were replaced by very light yellow ones. And they didn't mistake dark blue objects for the dark yellow ones either, suggesting that dogs can clearly distinguish between many different shades and colors, and don't just see in grayscale.

So the next time you ask your dog to fetch your blue slippers and he comes back with a pair of bananas, he's not colorblind, he's just messing with you.

[switch presenters]
Man, all this time, we've been selling dogs short. Now there's a lot of things we could put into episode, but for now, let's end on a big one: your senses. 

In grade school, you likely learned that you have five senses, and you may have even done games and activities to really help you remember what they are. Well, it's time to break out the markers and popsicle sticks out again, because you've got at least three more sense to add to your list. Here's one last video in which Hank explains.

[switch presenters]
Text: 3 Senses you didn't know you had 
At some point, you've probably learned about the five senses: sight, sound, smell, taste, and touch. But these five don't explain all of our sensations. How can we tell how hot or cold we are, or keep ourselves balanced? Now, scientists are beginning to add more senses to that classic list. 

Here are three of them. It should come as no surprise that sensing temperature is pretty important, which we call thermoception. It helps us keep our body temperature constant, and lets us know when our environment is too hot or too cold, so we can avoid tissue damage, like from burns or frostbite. So, how do we do it?

Scientists have found a couple of potential mechanisms connected with the transient receptor protein (TRP) channel, or "TRP family". There are lots of these channels, and they react to lots of different stimuli. We're still trying to figure out what they all do, but one thing's for sure: a lot of them help us to respond to changes in temperature. Scientists aren't exactly sure how these channels work, but with the physical stimuli of the environment getting warmer or colder, depending on the channel, they're more likely to open.

One of these channels, TRPV1, plays a role in the sensation of painful heat. The receptor is activated when temperatures get uncomfortably warm, around 40 degrees Celsius. TRPM8, on the other hand, responds to cold stimuli -- below 20 degrees Celsius (68 degrees Fahrenheit), so pretty much anything below room temperature.

These channels and others can be found throughout our bodies, but when they're on nociceptors -- or pain-sensing nerves -- activation of the channel triggers a rush of calcium into the cell, and sends a signal to the brain about painful temperature. All that information goes to the primary somatosensory cortex, a thick fold of tissue on the top of the brain where most of the mechanical sensations, like touch, pain, and vibration, are processed. Then you can consciously process the temperature and yank your hand away from that campfire, or decide whether you want to put on a jacket.

Now, have you ever thought about how you just know where your body is in space? Well, that's proprioception. The word comes from the Latin for "one's own grasp." It's how you can type without looking at a keyboard, and walk without looking at your feet. And there are a bunch of specialized receptors in our skin, joints, and muscles that help us do it.

For example, muscle spindles respond to changes in muscle length and the speed of muscle movement, while Golgi tendon organs send signals about muscle tension and exertion. And then cutaneous mechanoreceptors respond to stretch and pressure in the skin and joints.

All of these receptors work together to provide the brain, especially the cerebellum, with information about your movement and the positions of your limbs. The cerebellum is responsible for coordinating things like balance, posture, and voluntary movement.

Weirdly though, scientists recently discovered a case of a woman born without a cerebellum, who has some balance and movement issues, but seems to be doing relatively fine. So there is still a lot to understand how our brains process proprioceptive information.

Separately, we have equilibrioception, our sense of balance, and we need balance whenever we move, like walking and running. Ears are important for our sense of hearing, but they're also a key part of equilibrioception, especially the inner ear. It contains the vestibular system, which includes three fluid-filled semicircular canals lined with tiny hair cells. When your head moves, these hair cells are sloshed around by the fluid and send signals to the brain, specifically to the vestibular nuclei in the brainstem. Each canal is responsible for a different kind of movement: one for up and down, one for left and right, and one for side-to-side.

The otolith organs -- located just below the semicircular canals -- are similar, but in addition to liquid, they have tiny crystals made of calcium carbonate. As the head moves, these crystals rub against the hair cells attached to the membrane, which send information to the brainstem. Your brain then sends information out to your eyes, joints, and muscles, so they can respond accordingly and help you navigate the world.

Now, problems with this system can lead to issues with balance. Vertigo, for example, can be caused by loose stones in the otolith organs. They can also fall into the semicircular canals, disrupt the normal fluid movement, and put unexpected pressure on the hair cells. That pressure conflicts with what your eyes are seeing, which can make you feel dizzy when you move your head.

Together, these three sense are really important in helping us navigate our environment successfully and safely. So even though they don't make the list of our traditional senses, I think we do ourselves a disservice by forgetting about them. 

[switch speaker]
So, in a lot of ways, the world is way cooler than we learned when we're kids, and that's okay. It doesn't mean your teacher did a bad job, ...

or that you should have definitely learned what atoms really look like when you were seven or eight. Especially when you're first learning about science, it can be easier to take things one step at a time. And then, as we get older, we can learn that things are more complex than they seem. Thank you for watching this episode of SciShow, and thank you to all of our patrons who have made this show possible over the years. If you want to learn about more misconceptions that you might be carrying around, you can check out our episodes about animal misconceptions right after this.

[music]
[credits]