Flat Earth Week, Day 7: Water We Going To Do About It?


All things must come to an end, except for Earth, which does not have ends because it is not flat.  We have reached the final day of Flat Earth week.

And wouldn’t you know it?  I’ve just stumbled across a veritable gold mine of Stupid Bad Flat Earth memes in the form of the Facebook community Flat Earth Matters.  There are enough memes there for a dozen Flat Earth weeks, but alas, I would never write about anything else if I tried to tackle them all.  Perhaps I’ll revisit the topic another time.  Until then, we bid a fond adieu to the looniest of loony conspiracy theories, and what better meme to send us off than this stunning display of Flat Earth “physics”?

Now the obvious answer to this meme is “Yes it does, because gravity.”  But you have to remember that Flat Earthers often don’t believe in gravity.  More specifically, they don’t believe that Earth has gravity, although some of them allow the Sun, Moon, planets, and stars to have gravitational influence because they think that this patches holes in their rapidly sinking model.

I’ll explain how water is able to “stick to a ball spinning 1000 mph”, although I know it won’t convince the average Flat Earther.  That’s okay; this blog has never really been about convincing the other side.  I try to bring logic and evidence to the table while ranting about the stupidity of memes, and the reader may decide for himself or herself whether I have sufficiently made my case.

So let’s start by establishing that Earth does in fact have gravity.  Newton said that anything with mass has a gravitational influence on any other object with mass, and there’s no reason to believe that Earth is any different.  Henry Cavendish showed in 1798 that objects much less massive than Earth have their own gravitational sway, albeit minuscule.

Einstein overhauled Newton’s ideas by showing that gravitation is actually the result of massive bodies curving the fabric of spacetime.  In doing so, Einstein predicted that not only can gravity affect the motion of objects with mass, but it can bend the path of massless light as well.  The famous Eddington experiment of 1919 proved that Einstein was correct.

Although Newton’s and Einstein’s models of gravity vary in important ways, they agree in one important detail: the more massive an object is, the more gravitational influence it wields.  That’s why in the realistic model of the cosmos, the Moon orbits around Earth and Earth orbits around the Sun.

Now the average Flat Earther believes that the Sun and Moon are much smaller – and presumably less massive – than Earth is.  (Well, they’re correct about the Moon, but definitely not about the Sun.)  Let’s pretend that they’re right in both cases.  If the Sun is still massive enough to bend the light from distant stars in exact accordance with Einstein’s General Theory of Relativity (and it is), and if Earth’s mass is much greater than the Sun’s mass (which, according to Flat Earth models, it must be), then surely Earth’s mass is enough to exert a gravitational influence on the objects that rest upon it, right? In fact, Earth’s gravity ought to be enough to squash it into a ball.

Or are Flat Earthers prepared to admit that their model is inconsistent in that it treats Earth as a physically special object, separate from and immune to the laws that govern the heavenly bodies?  No, even the most fact-averse Flat Earther, if he is intellectually honest (he isn’t), must concede that Earth has mass; ergo, it also exerts a gravitational tug.

Earth has gravity, anyway you look at it.  And in the Globe Earth model (i.e. the correct model) Earth is indeed spinning at a seemingly high rate of speed.  However, your speed with respect to the center of Earth diminishes as you move away from the equator.


The difference in speed between diverse latitudes gives rise to the Coriolis effect, which causes the rotation of tropical storms and ocean currents (but has no effect on the direction your toilet flushes!)  The easily measurable rotation of wind and water currents is just one more piece of evidence that we live on a spinning, ball-shaped Earth.  But we were talking about gravity.

Using Newton’s Law of Universal Gravitation (which will do in a pinch, although it is not as complete or exact as General Relativity), we can calculate that gravity exerts a “force” of about 9.8 newtons (about 2.2 pounds-force) on every kilogram of mass near Earth’s surface.  Is that enough force to keep Earth’s water from flying off into space, especially near the equator where it is moving the fastest?  Let’s find out.

The force required to keep something moving in a circular path is called centripetal force.  The faster an object is moving, or the more mass it has, or the tighter the circle you want to keep it moving in, the more force is required.  For example, imagine swinging a bowling ball in a horizontal circle on the end of a chain.  (No, I don’t know where one might find a bowling ball attached to a chain…just go with me on this one.)  It would take more force to swing a 12-pound ball then it would to swing an 8-pound ball.  It would also take more force to keep a ball swinging in a circle  5 feet across, compared to a circle 10 feet across.

Using the centripetal force formula, we can show that at the equator, it only takes 0.034 newtons (0.0076 pounds-force) of force to keep a kilogram of water moving in a circle with the same radius as Earth.  But remember, Earth’s gravity provides about 9.8 newtons of force per kilogram of matter, which means that each kilogram of water experiences way more than enough force from gravity to prevent it from flying off into space, even at the equator where it is spinning the fastest.  Q.E.D.

Now you might reasonably ask: if Earth’s rotation is causing me to move at hundreds of miles per hour, why don’t I feel like I’m moving that fast?  The answer to that question is two-fold:

  1. Compared to the size of Earth, even 1000 mph is not a very high speed, and
  2. Everything around you, including the air, is moving with you at the same speed.

See, it’s all relative.  We live on a ball-shaped Earth that spins once a day, moving around the Sun at more than 67,000 miles per hour (30 kilometers per second).  The Sun itself is whizzing through space at hundreds of kilometers per second, depending on which reference frame you choose.  But to us tiny humans held fast to Earth by gravity, none of this is readily apparent.  It’s only when we take the time to study the universe that we see the truth.  Humans have been studying the Universe and our place in it for centuries; its only the Flat Earthers, Creationists, and other reality-denying ideologues who seek to turn back the clock of scientific progress.

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