Hey, Vsauce. Michael here. The Earth is spinning
and we are spinning along with it. But what if the
Earth suddenly stopped spinning? Well, first of all, you would
gain weight. But that would be the least
of your worries. The spin of our planet is important
and literally giving you the time of your life.
At the equator, the surface of Earth, and
everything on it, is spinning around at 465 meters per second.
As you move closer to the poles you don't have to move as quickly to complete
Earths daily rotation. Here in San Francisco, the Earth is driving me
east at 368 meters per second. If I could float above the surface
independent of the Earth's rotation, the Earth would spin underneath me
this quickly. Pretty cool. But, of course, when I jump straight up into the air,
the Earth doesn't move underneath me because I continued to spin with it.
We are all spinning with the Earth and that is why slamming on a set of
magical planetary breaks that caused everything
classically called earth to stop spinning would be catastrophic.
Immediately everything that wasn't
Earth, and wasn't safely at the poles, would continue moving, as it had been,
and be flung due east at more than a thousand miles an hour.
You wouldn't be flung into space because escape velocity is 24,800 mph
but your body would
instantly become a 9.5 inch caliber bullet.
Well, really more of a supersonic tumbleweed.
Because the atmosphere would more gradually slow down, people in airplanes,
assuming they could navigate the resulting storms, might have a better
chance of surviving.
Astronauts aboard the ISS would fare even better.
But it is unlikely that anyone would be waiting for them
down on the ground. Runways would just be
entrances to the new planet-sized graveyard,
created by the no longer spinning Earth.
People really really near the poles might be okay but
only at first. Gusts of wind, as fast as those near an atomic bomb detonation,
would blast, pass the surface and up into the sky forming worldwide storms
of unprecedented magnitude. The friction alone,
caused by the now stopped Earth colliding with these winds, would be enough to cause
massive fires,
unparalleled erosion and damage to anything strong enough to stay put
after the initial braking. The Sun would seem to freeze in the sky as days
became not 24 hours long but 365 days long.
Without spinning innards, Earth's protective magnetic field would cease to exist
and we would be dosed with deadly amounts of ionising radiation from the Sun.
The oceans would surge onto land in tsunamis kilometers high and wash over nearly
all dry land, before migrating to the poles,
where gravity is stronger, no longer held to the ocean basins by the inertia
Earth's spin gave them,
until Earth itself, no longer bulging an extra 42 kilometers around its equator, because
of its rotation
slowly compressed into a more perfect sphere
than it is now. Possibly allowing the oceans to eventually return somewhat.
That is what would occur
if it actually happened. It won't actually happen but
woah, its rotation is slowing down.
More on that later. First, if the Earth really is spinning so quickly,
why can't we feel it? Why doesn't the Earth's rotation
make us dizzy? Well, lucky for us,
the change in velocity is just too gradual. The Earth is too huge.
It's like driving in a car that takes
6 hours and six thousand miles to make one
left turn. It's not sudden enough to register
with our senses. But that change in velocity
is real and it makes us way
less, because of inertia. On our spinning planet your velocity is constantly
changing but always
tangential to the circular path you were being dragged along.
Now, because inertia is a property of matter, which includes
your body, without a force acting upon us we would
slowly leave the surface of Earth.
Luckily, the Earth is exerting a force on us. A center-seeking,
centripetal force, delivered by gravity.
The centripetal force required to keep you along a circular path with Earth is subtracted
from Earth's total gravitational pull on you.
The remaining force simply pushes you down,
toward the centre of the Earth - it gives you weight.
At the equator, if the Earth didn't spin, and no centripetal force was required to
keep you
with the Earth, you would weigh 0.3 percent
more than you currently do. If Earth spun you around
17 times faster than it currently does, all of its gravitational force
would go toward centripetal force fighting against your inertia
and you would be weightless.
So here's a diet idea. Hope that the Earth starts
spinning faster and go back for guilt-free seconds.
Seconds.
We know exactly how long
a second is. The outermost electron
of an atom of cesium 133 is alone.
When the atom is undisturbed, only the nucleus
interacts with this outermost electron, tickling it
regularly and rapidly between two levels.
After 9,192,631,770
oscillations between those two levels, one second has passed.
Exactly.
That is literally the definition of a second.
We can measure and count those oscillations.
It's how atomic clocks work. Making atomic clocks,
the most accurate measurement device ever built by humans, to measure anything.
We can't define
a second more simply, as say, 1/60th of 1/60th of 1/24th of a day
because of Earth's spin.
It's too irregular. Little changes
in the distribution of mass on Earth, caused by earthquakes or melting ice
or man-made dams or technically
even you walking up stairs or downstairs,
cause Earth's rotational speed to change.
Like a figure skater moving their arms further away from or closer to their bodies.
Now add on top of that the fact that tides, caused by the Moon,
drag against Earth's rotation and you wind up with an
unstable rotation speed that is
predominately slowing down.
Now, these changes are incredibly incredibly slight, but over time
they add up. In 140 million years,
a day on earth will not be 24 hours long,
it will be 25. That might not sound like much
but in order to do important things, like deliver accurate GPS information,
we need a more accurate timekeeping device
than that. So, as a solution
scientists keep the pace of seconds using atomic clocks,
TAI time. And other scientists
measure the changing speed of Earth's rotation by observing distant stars
and quasars. Now, every few months they find out just how behind or ahead
Earth is running, and if it's getting too close to being a second
off, they decide to add or subtract the second from the current year.
The result is the time used almost everywhere,
including your phone: UTC.
Since this system began in 1972
25 leap seconds have been added.
What this means is that clock time is,
and has to be, a manufactured
product with upgrades and tune ups administered
periodically, after defects
are noticed. The time we give to now
and the future is only ever
approximate. That's weird
but it's also entirely not weird.
As Demetrios Matsakis, the Chief Scientist of Time Services for the US
Naval Observatory puts it,
"we save lives
and we end lives. We add time and we can take time away,
but in both cases we do so without completely
understanding exactly what life is,
or what time is."
Regardless, thank you for spending some of yours with me...
and as always,
thanks for watching.