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  • Flying in a 747 from one side of the earth to the exact opposite side would take about

  • 22 hoursand while I know there's a bit of rock in the way, that's really going the

  • long way round.

  • So what if we did dig a hole all the way through the earth, through the center, and jumped

  • in?

  • Well, Michael, you probably would't make it very far - that's because of the Coriolis

  • effect (which is why a ball curves weirdly when you toss it while riding a merry go round

  • and why hurricanes always spin counterclockwise in the northern hemisphere). At the equator,

  • the earth (and you on it) is rotating eastwards at 1670 km/hr. As you go deeper, the bits

  • of earth around you are still spinning around once per day, but they don't have as far to

  • travel so they're going at slower and slower speeds. If you jumped into a vertical shaft,

  • you'd soon be traveling east faster than the rock around you so that after falling only

  • a few kilometers, you'd crash into the eastern wall. It might not be a disaster, but some

  • miners near Lake Superior tried to test this by dropping cannon balls down a mile-long

  • shaft - and the balls never reached the bottom.

  • OK, so what if the tunnel went from pole to pole, so the Coriolis effect didn't apply,

  • and let's also assume that there's no air resistance, or friction

  • Ok. Since the earth's mass is more concentrated close to the middle, gravity would pull you

  • down with roughly the same amount of force for the first 3000 km, or halfway to the center

  • of the earth - this familiar, constant force would accelerate you until you were falling

  • 8km every second, and the trip halfway to the middle of the earth would only take 13

  • minutes. Soon after, you'd reach the earth's outer core, and this is the point in your

  • journey where the pull of gravity would be strongest - but only slightly stronger than

  • the force we're used to on the surface.

  • As you continued to fall closer to the center, so much of the earth's mass would now be above

  • you that it would begin to seriously cancel out the attraction of the mass below, and

  • the pull would weaken until you reached the center. Here, you'd experience no gravitational

  • pull at all - or rather, the earth would be pulling on you the same amount in all directions,

  • so you could float freely around with no sense of "up" or "down". Except, remember, that

  • you'd be speeding past at 22,000 miles per hour, or 6 miles a second.

  • Once you passed the center, the whole process would reverse and you'd gradually slow, pulled

  • down (or is it up?) weakly at first and then more strongly, until when you got to the other

  • side, you'd stop moving and could step out on the surface, a mere 37 minutes, or one

  • dryer cycle, later.

  • Of course, the deepest we've ever been able to dig is the Kola Superdeep borehole in Russia.

  • But it only went down 12km, which is only two thirds the length of Manhattan. They had

  • to stop because it got too hot: 180°C. And this is sort of the problem with digging a

  • hole through earth - earth is hot, and molten in the middle. You can't just dig a hole through

  • it with shovels. But here's a question: wasn't the middle of earth wasn't all "liquidy",

  • what if earth was hollow, but weighed the same?

  • Well, with its entire mass concentrated in a thin shell right under our feet, the earth

  • wouldn't have a magnetic field any more, because that comes from the molten iron core. So we'd

  • be totally vulnerable to radiation from the solar wind and storms, and this means we'd

  • see the aurora EVERYWHERE. Look! The NorthernSouthernEastern lights!

  • And if you jumped inside the hollow earth to escape the solar storm? Well, gravity from

  • the different parts of the spherical earth-shell would perfectly cancel out and you'd float

  • freely about inside as if the earth weren't there at all! Of course, you'd better bring

  • a space suit, because there's not nearly enough air ON earth to fill up the entire INSIDE

  • of earth. But what if the entire inside of the hollow earth were covered with mirrors?

  • Henry, that's ridiculousfor now

  • Ok, so back outside of the earth, we wouldn't really notice much difference from a gravitational

  • perspective - falling things would still accelerate at 9.8 m/s^2, a baseball would follow the

  • same trajectory, and the moon would follow the same orbit around the earth.

  • Hey Henry, let's go to outer space, right now. Bring your gun - this'll all make sense

  • later. C'mon.

  • Oh, and you're coming too. Click this annotation to head over to my channel, Vsauce, to see

  • the rest of our adventures. I'll see you over there.

Flying in a 747 from one side of the earth to the exact opposite side would take about

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B1 earth hollow km center jumped pull

What if the Earth were Hollow?

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    Why Why posted on 2013/03/29
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