this post was submitted on 15 Feb 2025
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Science Memes

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[–] troyunrau 96 points 2 weeks ago (17 children)

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...

[–] [email protected] 44 points 2 weeks ago (5 children)

OK now how fast did old man's head move

[–] troyunrau 67 points 2 weeks ago (4 children)

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.

[–] [email protected] 3 points 1 week ago (1 children)

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!

[–] troyunrau 1 points 1 week ago (1 children)

It's very possible. Napkins are notorious for stealing orders of magnitude.

[–] [email protected] 1 points 1 week ago

What is a factor of 1000 between friends anyway? (Especially cosmologist friends)

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