# Physics 101: Please settle a bar bet (collision physics) **URL:** \ **Category:** Factual Questions\ **Created:** [January 18, 2023, 10:09pm UTC](https://boards.straightdope.com/t/physics-101-please-settle-a-bar-bet-collision-physics/978429 "2023-01-18T22:09:36Z")\ **Posts on this page:** 8\ **Page:** 5
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [January 20, 2023, 4:38pm UTC](https://boards.straightdope.com/t/physics-101-please-settle-a-bar-bet-collision-physics/978429/81 "2023-01-20T16:38:09Z")
The difference here is that the OP (as previously stated) did not define the parameters. > [@Sitnam](#): > > At the point of impact, are the forces the same? In particular - the “forces” on what. My concern is for the passengers and the extent of their injuries rather than the mathematics of forces. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [January 20, 2023, 4:39pm UTC](https://boards.straightdope.com/t/physics-101-please-settle-a-bar-bet-collision-physics/978429/82 "2023-01-20T16:39:36Z")
ETA: and I’m ninja’d by @bob_2. Excellent point there @Riemann. A lot of why people get these collision scenarios wrong is they’re applying intuition to the whole scenario, including the secondary stuff. The primary collision is properly modeled as two spherical cows (or one spherical cow and an absolutely unyielding immovable planar wall) where the cow(s) are made of something like clay or putty that uniformly smooshes (technical term) on impact. Which is good basic physics, but the model leaves out a lot of real-world factors that apply to actual car crashes. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [January 20, 2023, 4:54pm UTC](https://boards.straightdope.com/t/physics-101-please-settle-a-bar-bet-collision-physics/978429/83 "2023-01-20T16:54:05Z")
> [@bob\_2](#): > > In particular - the “forces” on what. My concern is for the passengers and the extent of their injuries rather than the mathematics of forces. > [@LSLGuy](#): > > Which is good basic physics, but the model leaves out a lot of real-world factors that apply to actual car crashes. I think it is a reasonable simplification that the substantial primary harm is caused by the immediate rapid deceleration and crushing of the car(s), with the passengers secured in the interior of the car during that brief time. In that respect, the forces on the passengers are identical. The magnitude and duration of the deceleration is the same (i.e. the “g-force” experienced by the passengers is the same), the amount of crushing of the car(s) is the same. My joke about the spherical cow was not intended as an implication that this is totally unrealistic. The validity of the approximation as a prediction of the ultimate harm is no doubt weaker as the absolute speeds get higher, because at very high speeds cars are completely disintegrating and people are flying everywhere, so speed relative to the ground is important. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [January 20, 2023, 5:24pm UTC](https://boards.straightdope.com/t/physics-101-please-settle-a-bar-bet-collision-physics/978429/84 "2023-01-20T17:24:02Z")
Of course, the other simplifying assumption is the unyielding wall of infinite mass. If you swerve to avoid an oncoming car and hit a massive concrete pillar supporting a freeway overpass, you have saved the people in the other car but you probably haven’t helped yourself at all. If you swerve and hit something with any capacity to deform or move, you’re better off. ---
**Author:** ![Sitnam](https://avatars.discourse-cdn.com/v4/letter/s/6a8cbe/32.png) [@Sitnam](https://boards.straightdope.com/u/Sitnam)\ **Post date:** [January 20, 2023, 6:10pm UTC](https://boards.straightdope.com/t/physics-101-please-settle-a-bar-bet-collision-physics/978429/85 "2023-01-20T18:10:42Z")
> [@bob\_2](#): > > The difference here is that the OP (as previously stated) did not define the parameters. > > > [@Sitnam](#): > > > > At the point of impact, are the forces the same? > > In particular - the “forces” on what. My concern is for the passengers and the extent of their injuries rather than the mathematics of forces. I assure you, the passengers and any injuries they may suffer are purely hypothetical. Would it make any difference if the Corolla was driving into a hill of pillows? ---
**Author:** ![smithsb](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/smithsb/32/12107_2.png) [@smithsb](https://boards.straightdope.com/u/smithsb)\ **Post date:** [January 20, 2023, 7:34pm UTC](https://boards.straightdope.com/t/physics-101-please-settle-a-bar-bet-collision-physics/978429/86 "2023-01-20T19:34:51Z")
> [@Riemann](#): > > My joke about the spherical cow was not intended as an implication that this is totally unrealistic. I thought it was a nice touch, carry on. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 21, 2023, 3:06pm UTC](https://boards.straightdope.com/t/physics-101-please-settle-a-bar-bet-collision-physics/978429/87 "2023-01-21T15:06:38Z")
> [@Sitnam](#): > > Would it make any difference if the Corolla was driving into a hill of pillows? Yes, of course. A hill of pillows is significantly more yielding than either a car or a concrete wall. ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [January 21, 2023, 5:55pm UTC](https://boards.straightdope.com/t/physics-101-please-settle-a-bar-bet-collision-physics/978429/88 "2023-01-21T17:55:32Z")
Its probably also good to talk about the engineering aspects of car collisions : namely that there are carefully selected crumple zones, so that the collision is inelastic; sorta like a putty hitting a wall. At the same time, the crumple zones are engineered to keep the space around the people in the car as much protected as possible. For example : most modern car engines fall off during a collision, thereby removing a significant mass in front of the driver. Also, although in the ideal physics world, small object “collisions” like with a mosquito does not cause much damage. In the real world though, a small pebble (like a piece of ceramic or alumina) can destroy a windshield and cause massive damage to passengers and hence windshields are engineered to be of laminated glass. Laminated glass does not shatter and is another protective layer. At high speeds, like airplanes, air resistance comes into play. A small collision can leave a “hole” that can potentially bring down the plane. [Previous page](https://boards.straightdope.com/t/physics-101-please-settle-a-bar-bet-collision-physics/978429.md?page=4)