So right when you see this, before we even talk about me and Earth, or needles and Earth, or taxi cabs and Earth and that force of gravity, you might have something bizarre raising up in your brain.
![cool math gravity guy cool math gravity guy](http://coolmathgameskids.com/wp-content/thumbs/fireboy-and-watergirl.gif)
So really it's from roughly the distance from the surface of the Earth or if I'm roughly five foot-nine then about half of that distance to the center of the Earth is this number right over here. The center of me and center of the Earth. Then this is the distance between the center of masses between those two objects. You pick one of the masses to be Earth, so this mass over here. So if you're talking about the force of gravity on Earth, this right over here. Which is a super-duper small number, times the mass of the first object, times the mass of the second object, divided by the distance between the two objects. It's equal to this constant, this gravitation constant. is going to be equal to this this big G, which is really just a number, its a very small number. The force of gravity between two objects. And in it, he theorizes that the forces between objects now it's a vector quantity, it's always going to attract the two objects to each other. And he formulated the universal Law of gravitation, or the law of universal gravitation either way. So, as you can imagine, the thing that Isaac Newton believes brought the apple to the Earth is gravity. But he actually formulated an entire, an entire. There's something that might be pulling, somehow, acting on this apple, bringing it to the earth. And not only was he able to kind of think that there's something.
![cool math gravity guy cool math gravity guy](https://www.coolmathgameskids.com/wp-content/uploads/2018/01/superfighters-ultimate.png)
But for most purposes, when we're engineering things on the surface of the planet, and we are not going close to the speed of light, we can still use the mathematics that Isaac Newton came up with from this simple question. It has been tweaked a good bit by this gentleman in the last hundred years. He actually asked the question why? Does it always have to be that way? And that question took him down a entire line of reasoning that set up the basis for all of classical mechanics for the most part we still use today. But for Isaac Newton, at least on that day, he asked himself, "Why? Why did that apple fall?" And this, to some degree, is a great example of "out of the box" thinking, because something for thousands of years or tens of thousands of years human beings had taken for granted, just because that's the way it always was. And if most people were to see that, they would just think it's a normal happening in the universe. If i were to snap this twig over here, the apple would fall. It's probably not true that you'll see in some cartoons on television that the apple hit his head or hit his head while he was sleeping and gave him the idea. And one of his big insights about this 'things falling down' problem is: Do they have to fall down? Is this just something we should assume about the universe? Things just need to fall down, he said, or we were told he said that he was somewhat inspired by observing an apple falling from a tree. Easily one of the top five minds in all of human history. And this, as you may already know, is Isaac Newton. He did many more things than just the things I am going to describe in this video, and any one of those things would have earned him his place in history.
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![cool math gravity guy cool math gravity guy](https://www.coolmathgameskids.com/wp-content/uploads/2016/05/maxploder.png)
To think otherwise would just be crazy." And that's why this guy, this guy right over here, is one of the greatest geniuses of all time. We thought, "well look it's just obvious, everything should just fall down, that's just the way the universe is. And so, for most of human history or human civilization, we just accepted it as a given. And so it is just a thing that is fundamental to everything that we have ever ever experienced. If i had a needle at rest here it doesn't just automatically for no reason jump and fly upwards and start to float. If i were to drop a bunch of needles they would just fall. It is just trying to get lower and lower and lower. Not only will the water fall, it will hit the ground, it will puddle up, and if there is a gutter it will fall into the gutter. You don't have taxi cabs that float around, they'll fall. That you don't have people that are able to just float around, they will fall. If they are small enough they are being held up by the wind and all that, but if they are large enough, they will fall. Everything in human experience, and really human history or human civilizations experience, is that everything seems to fall to the earth, that if you have water particles, they don't just float up.