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 it's 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. [SciShow Intro video] Okay, probably not everyone. 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 shoot off in straight lines. There would be no galaxies or solar systems or planets and the universe would be an supremely boring place. So let's talk real quick about how gravity works. This equation 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, 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 toward 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. This 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 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 the objects equally. So let's go back to Isaac's equation, whatever we do to that distance number, no matter how big, how far things are apart, 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're sitting there motionless, you're not floating, you're 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. Space, wall-to-wall with gravity. Thank you for watching this episode of SciShow. If you have any questions or comments or ideas, you can leave them on Facebook or Twitter, or, of course, down in the comments below, and if you want to keep getting smarter with less here at SciShow you can go to youtube.com/SciShow and subscribe. [SciShow Outro]