She knows, because aliens speak to her through the Internet. In 2012, a "Planet X", which is currently orbiting on the opposite side of the sun at the exact same radial velocity as the Earth, will accelerate past the Earth, and Planet X's gravitational pull will cause the Earth to start rotating the opposite direction. This will happen so fast, that the atmosphere will continue on at its same speed, causing 600-mph winds and general mayhem across the world.

Now, I knew this was absurd, but I couldn't prove it. So I did.

The Earth's equatorial diameter is about $40.0 \times 10^{6} m$, in Flagstaff, Arizona (about where she lives) which is at 35° of Latitude, that diameter is $D_{equator} \cdot cos(35^{\circ}) = 32.8 \times 10^{6} m$

The Earth rotates once a day, giving us an angular velocity (at $35^{\circ}$) of:

$72.7 \times 10^{-6} \frac{rad}{s} = 379 \frac{m}{s} = 878 \frac{mi}{hr}$

So stopping the Earth instantly would produce 878mph winds. I'm not sure of the fluid dynamics of the atmosphere, and so can't estimate the slowdown time that would give a $\Delta V$ of 600mph, but it doesn't matter because:

The kinetic energy of a rotating sphere is:

$E_k = \frac{1}{2} I \omega^2$

where I is the moment of inertia of a solid sphere, and ω is the angular velocity in radians per second. The moment of inertia is calculated as:

$I_{sphere} = \frac{2}{5} m R^2$

which leads to the expanded equation of:

$E_k = \frac{1}{5} m R^2 \omega^2$

The Earth's mass is approximately $5.97 \times 10^{24} kg$ and its radius about $6.38 \times 10^{6} m$, so, the energy required to stop the Earth's spin is:

$E_k = \frac{1}{5}(5.97 \times 10^{24} kg)(6.38 \times 10^{6} m)^2(72.7 \times 10^{-6} \frac{rad}{s})^2 = 257 \times 10^{27} J$

That’s 257 octillion or 257 million-billion-billion Joules. Putting that in perspective, we receive about $1.37 \times 10^{3} \frac{W}{m^2}$ from the sun, or $701 \times 10^{15} \frac{J}{s}$, so the energy required to stop the Earth’s rotation in 1 day is enough to heat and light the Earth for eleven thousand years. Assuming that the energy transfer from “Planet X” or the aliens is 90% efficient, that leaves $25.7 \times 10^{27} J$ of waste energy, probably being converted to heat. That’s enough energy to raise the temperature of all the Earth’s oceans 4,527°C or to 8,211°F, which is just colder than the surface of the Sun.

And if you followed that, ladies and gentlemen, you are either a physics major, or an engineer.

This is a historical cross-post of a short-lived feature I posted on Facebook called "You Might Be an Engineer If..." with a slight edit. The original post can be found (for now) here.

To help with this transition, here is the "If EE manufacturers were past girlfriends..."

TI is the high-maintenance debutante. There's no other way you're vacationing in the Hamptons, but you have to put up with a lot of overhead and runaround.

Microchip is the social outcast. It may not be kosher to talk about the relationship in public, but she's always easy to please and her ideal date is hole-in-the-wall Mexican and a night browsing the web.

Maxim is the bookish girl down the street. People might make fun of the fact that you're friends with her, but somehow, she's always ready to take care of whatever you need.

On Semiconductor is the ex you run into at your high school reunion. She's the same shallow girl you knew 15 years ago, but somehow the new look makes you want to try again.

ARM is the girl you met while backpacking across Europe. You never really got to know her, and you can't reminisce about her with your friends, but every few weeks you're inexplicably reminded of how awesome she was.

National Semi. is the hairdresser. Turns out, she's the real reason all your other girlfriends were so attractive.

Atmel is the babysitter. She's great in her own right, but all those kids she hangs around with left a bad taste in your mouth.

Zilog is the girl your friends said was "robbing the cradle". If you're willing to overlook the fact that she's a little behind everyone in the maturity department, she's a great girl.

IBM is the feminist. It wasn't good, and it ended badly, but she's the reason the rest of the girls can wear miniskirts in public, so you have to respect her.

Intel is the hot-but-crazy chick it seemed everyone had dated. All your friends warned you against her, you ignored them, and after it was over you felt a little dirty.

This is a historical cross-post of a short-lived feature I posted on Facebook called "You Might Be an Engineer If..." with a slight edit. The original post can be found (for now) here.