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  • (Music)

  • You probably already know that everything is made up of

  • little tiny things called atoms.

  • You might even know that each atom is made up of even smaller particles

  • called protons, neutrons and electrons.

  • And you've probably heard that atoms are small.

  • But I bet you haven't ever thought about how small atoms really are.

  • Well, the answer is that they are really, really, really small.

  • So you ask, just how small are atoms?

  • To understand this, let's ask this question:

  • How many atoms are in a grapefruit?

  • Well let's assume that the grapefruit is made up of only nitrogen atoms,

  • which isn't at all true, but there are nitrogen atoms in a grapefruit.

  • Well, to help you visualize this, let's blow up each of the atoms

  • to the size of a blueberry.

  • And then how big would the grapefruit have to be?

  • It would have to be the same size of -- well, actually, the Earth.

  • That's crazy! You mean to say that if I filled the Earth with blueberries,

  • I would have the same number of nitrogen atoms as a grapefruit?

  • That's right! So how big is the atom?

  • Well, it's really, really, really, really small.

  • And you know what?

  • It gets even more crazy.

  • Let's now look inside of each atom -- and thus the blueberry, right? --

  • What do you see there?

  • In the center of the atom is something called the nucleus,

  • which contains protons and neutrons,

  • and on the outside you'd see electrons.

  • So how big is the nucleus?

  • Well, if atoms are like blueberries in the Earth, how big would the nucleus be?

  • You might remember the old pictures of the atom from your science class,

  • where you saw this tiny dot on the page with an arrow pointing to the nucleus.

  • Well, those pictures, they're not drawn to scale,

  • so they're kind of wrong.

  • So how big is the nucleus?

  • So if you popped open the blueberry

  • and were searching for the nucleus,

  • you know what? It would be invisible.

  • It's too small to see!

  • OK. Let's blow up the atom -- the blueberry --

  • to the size of a house.

  • So imagine a ball that is as tall as a two-story house.

  • Let's look for the nucleus in the center of the atom.

  • And do you know what? It would just barely be visible.

  • So to get our minds wrapped around how big the nucleus is,

  • we need to blow up the blueberry, up to the size of a football stadium.

  • So imagine a ball the size of a football stadium,

  • and right smack dab in the center of the atom,

  • you would find the nucleus, and you could see it!

  • And it would be the size of a small marble.

  • And there's more, if I haven't blown your mind by now.

  • Let's consider the atom some more. It contains protons, neutrons and electrons.

  • The protons and neutrons live inside of the nucleus,

  • and contain almost all of the mass of the atom.

  • Way on the edge are the electrons.

  • So if an atom is like a ball the size of a football stadium,

  • with the nucleus in the center, and the electrons on the edge,

  • what is in between the nucleus and the electrons?

  • Surprisingly, the answer is empty space.

  • (Wind noise)

  • That's right. Empty!

  • Between the nucleus and the electrons, there are vast regions of empty space.

  • Now, technically there are some electromagnetic fields,

  • but in terms of stuff, matter, it is empty.

  • Remember this vast region of empty space

  • is inside the blueberry, which is inside the Earth,

  • which really are the atoms in the grapefruit.

  • OK, one more thing, if I can even get more bizarre.

  • Since virtually all the mass of an atom is in the nucleus --

  • now, there is some amount of mass in the electrons,

  • but most of it is in the nucleus --

  • how dense is the nucleus?

  • Well, the answer is crazy.

  • The density of a typical nucleus

  • is four times 10 to the 17th kilograms per meter cubed.

  • But that's hard to visualize. OK, I'll put it in English units.

  • 2.5 times 10 to the 16th

  • pounds per cubic feet.

  • OK, that's still kind of hard to figure.

  • OK, here's what I want you to do.

  • Make a box that is one foot by one foot by one foot.

  • Now let's go and grab all of the nuclei from a typical car.

  • Now, cars on average weigh two tons.

  • How many cars' nuclei would you have to put into the box

  • to have your one-foot-box have the same density of the nucleus?

  • Is it one car? Two? How about 100?

  • Nope, nope and nope.

  • The answer is much bigger.

  • It is 6.2 billion.

  • That is almost equal to the number of people in the Earth.

  • So if everyone in the Earth owned their own car --

  • and they don't --

  • and we put all of those cars into your box,

  • that would be about the density of a nucleus.

  • So I'm saying that if you took every car in the world and put it into your one-foot box,

  • you would have the density of one nucleus.

  • OK, let's review.

  • The atom is really, really, really small.

  • Think atoms in a grapefruit like blueberries in the Earth.

  • The nucleus is crazy small.

  • Now look inside the blueberry, and blow it up to the size of a football stadium,

  • and now the nucleus is a marble in the middle.

  • The atom is made up of vast regions of empty space.

  • That's weird.

  • The nucleus has a crazy-high density.

  • Think of putting all those cars in your one-foot box.

  • I think I'm tired.

  • (Yawning)

(Music)

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B2 US TED-Ed nucleus atom grapefruit blueberry size

【TED-Ed】Just How Small is an Atom? - Jon Bergmann

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    Furong Lai posted on 2012/11/30
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