June 26, 2026
Speed kills... the comments too
Why does kinetic energy increase quadratically, not linearly, with speed? (2011)
Why going twice as fast can wreck way more than twice as hard — and the comments spiraled
TLDR: The post argues that motion energy rises with speed squared because the laws of motion must work the same from different moving viewpoints. In the comments, readers split between loving the crash examples, offering simpler shortcuts, and openly confessing that physics makes their brains melt.
A seemingly simple question — why speed makes energy shoot up so fast — turned into a full-blown physics feelings dump. The original post tries to answer it in a surprisingly elegant way: not with schoolbook formulas first, but with a thought experiment about lumps of clay, trains, and crashes. The big idea is that if the rules of motion have to look the same whether you’re standing still or riding along smoothly, then the energy of motion has to grow with the square of speed, not just step up in a neat straight line.
But honestly? The real spectacle was the comment section. One camp wanted the quick-and-dirty answer: car crash math. A wildly popular example compared two identical cars, one going 70 and one going 100, and people loved it because it makes the stakes instantly real: a little more speed can mean a lot more smashing. Another crowd tried to rescue intuition by saying power feels more natural than energy, while one exasperated commenter basically posted a public cry for help, admitting physics feels like “random tricks” even though math and computer science make sense to them. That confession hit hard.
And then there was the classic internet energy: one person dropped a breezy “Because it’s not momentum. ;p,” while another simply commanded everyone to “read Ron Maimon.” So yes, the article is about motion — but the comments are about something bigger: why physics makes some people feel enlightened, others feel cursed, and everyone suddenly starts arguing about car crashes.
Key Points
- •The article argues that explaining kinetic energy through work as force times distance does not by itself answer why the velocity dependence is quadratic.
- •The main derivation uses Galilean invariance and defines kinetic energy as heat produced when a moving clay ball collides with a wall.
- •From collision symmetry and conservation of energy across different reference frames, the article concludes that kinetic energy must scale with mass and velocity squared.
- •The article states that kinetic energy must be proportional to mass because two identical clay balls produce twice the heat of one in otherwise identical impacts.
- •A second derivation claims quadratic kinetic energy follows if gravitational potential energy near Earth's surface is linear in height and falling bodies undergo constant acceleration.