2 ms·

That’s not the argument he is making. He is making the argument that if you imagine a sheet of paper in between the 2 cars into which they crash, then since the

by dools 2y ago

That’s not the argument he is making. He is making the argument that if you imagine a sheet of paper in between the 2 cars into which they crash, then since they both stop since they are perfectly symmetrical then the fact that there is another car on the other side of the sheet is immaterial. It’s complete garbage.

kazinator 2y ago
Pardon me, I seem to have made exactly the same argument myself, completely with crude pictures. https://news.ycombinator.com/item?id=40629971 https://news.ycombinator.com/item?id=40629971 It is entirely unassailable; all you can argue with is the realism of my assumptions. (Real head-on collisions won't be precise mirror images.) When two identical objects are moving toward each other with a relative speed v, the collision is like hitting an ideal barrier at speed v/2.
- dools 2y ago
  CROSS POST: I posted this in reply to your linked explanation. Okay yep I get it now. The 4mv2 did it for me mathematically but I still couldn't get it intuitively until I imagined a car going 50mph rear ending a car going 40mph. If they wind up going the same speed as a result of the collision then the deceleration felt by the car in the back would only be 10mph if the car in front didn't change speed because it was like, an ocean liner. If the cars are the same size and the collision is perfect and all that then the car in front would gain 5mph and the car behind would lose 5mph. Since in a head on, they are both changing speed then the deceleration must be half the combined relative deceleration. The way I was imagining it was as if the car collides with another car going 50mph in a head on collision and the other car doesn't slow down due to the collision. So it appears that it is I who am confidently wrong about physics (although I still hold that Milton Friedman is confidently wrong about economics!).

by dools 2y ago

kazinator 2y ago

Pardon me, I seem to have made exactly the same argument myself, completely with crude pictures. https://news.ycombinator.com/item?id=40629971 https://news.ycombinator.com/item?id=40629971 It is entirely unassailable; all you can argue with is the realism of my assumptions. (Real head-on collisions won't be precise mirror images.) When two identical objects are moving toward each other with a relative speed v, the collision is like hitting an ideal barrier at speed v/2.

dools 2y ago
CROSS POST: I posted this in reply to your linked explanation. Okay yep I get it now. The 4mv2 did it for me mathematically but I still couldn't get it intuitively until I imagined a car going 50mph rear ending a car going 40mph. If they wind up going the same speed as a result of the collision then the deceleration felt by the car in the back would only be 10mph if the car in front didn't change speed because it was like, an ocean liner. If the cars are the same size and the collision is perfect and all that then the car in front would gain 5mph and the car behind would lose 5mph. Since in a head on, they are both changing speed then the deceleration must be half the combined relative deceleration. The way I was imagining it was as if the car collides with another car going 50mph in a head on collision and the other car doesn't slow down due to the collision. So it appears that it is I who am confidently wrong about physics (although I still hold that Milton Friedman is confidently wrong about economics!).