this post was submitted on 15 Feb 2025
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Okay, just back of the envelope math. Assuming the car is truly 550nm, so the blue car is 400nm, and the red car is 700nm... How fast is the car going?
Napkin math says 0.27c.
Δλ=λ(V/c)
Now someone else can figure out the kinetic energy of the car and why the whole continent just exploded...
It's not on fire or melting the asphalt beneath it, so it must be really aerodynamic, and have really low rolling resistance tyres...
OK now how fast did old man's head move
Okay, napkin math... his nose is about 20cm long, and assuming it rotated about a perfect circle. The car moved say 10m. At the speed the car is moving, it covers that distance in ~120ns. So he has to move the end of his nose around a quarter circle of radius 20cm in 120ns. Let's say 30cm total movement, for easy math. 0.25cm/ns or 0.00025m/ns. The speed of light is 0.300m/ns, so we're talking about ~0.001c at the tip of his nose. Which is incidentally very close to the speed of sound in air.
So, probably not quite a sonic boom off the end of his nose. Assuming my math is correct. Very strong neck muscles. Also, he's been vapourized.
Ah this is so great. In the transonic regime (just below 1.0 Mach) the air moving over the surface of his nose will break the speed of sound as it gets out of the way.
I think you missed a factor of 1000 when comparing against the speed of sound in air. I think it should be almost 1000 times the speed of sound, so definitely sonic boom and definitely vaporised!
It's very possible. Napkins are notorious for stealing orders of magnitude.
What is a factor of 1000 between friends anyway? (Especially cosmologist friends)
Did you take into account that the car is not driving directly towards the viewer?
I ain't doing hyperbolic equations on my napkin ;)
So about 180 million MPH. I hope he doesn't get a ticket!
now calculate the Lorentz contraction
Instructions unclear, car stuck in dick.
Why explode, the car didn't accelerate or interact with the continent
Even ignoring the tires interacting with the road, you have air molecules. I don't think that would be enough to destroy a continent, but it would be very destructive.
Here is a cool What If? from xkcd about throwing a baseball at 0.9c.
Sound like a ton worth of mass would do a lot of damage indeed
Wow, that seems to be the very first What If ever!
For the same reason this baseball causes an expanding plasma-ball disintegrating everything. Fusion with air molecules that can't get out of the way fast enough https://what-if.xkcd.com/1/