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Re: Elastic Collision

From pa@see.signature.invalid (Pierre Asselin)
Newsgroups sci.physics.research
Subject Re: Elastic Collision
Date 2026-02-13 18:05 -0800
Organization PANIX Public Access Internet and UNIX, NYC
Message-ID <10mo3cb$kh8$1@reader2.panix.com> (permalink)
References <10mhc4k$avqk$1@dont-email.me> <10mlemh$1pima$1@dont-email.me>

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Luigi Fortunati <fortunati.luigi@gmail.com> wrote:
> Il 12/02/2026 07:30, Luigi Fortunati ha scritto:
> > The Wikipedia entry for "Elastic collision"
> > https://en.wikipedia.org/wiki/Elastic_collision
> > contains the following animation
> > https://youtu.be/wl0c6NMysY4
> > where the two bodies collide at point x and instantly reverse direction.
> [ ... ]

> I dispute what the moderator wrote.

> A body of mass 2m cannot bounce back (in place!) when it collides with a 
> body of mass m,

And yet, it bounces back, though with a reduced velocity.


> otherwise a body of mass 3m, 10m, or 100m would also bounce back.

No, a body of mass 3m would stop cold, and bounce the body of mass m with velocity 2*v.
More massive bodies would continue forward with reduced velocity, and bounce the smaller
body with increased velocity.


> It's obvious that a body of mass 100m, colliding with a body of mass m, 
> can only slow down but not stop in place and bounce back!

Slows down a bit and bounces the smaller body with velocity approaching 3*v.
The formulas are in the text above the animations. (Mind the signs of the vA1,vB1 and vA2,vB2.)

-- 
pa at panix dot com

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Thread

Elastic Collision Luigi Fortunati <fortunati.luigi@gmail.com> - 2026-02-11 22:30 -0800
  Re: Elastic Collision Luigi Fortunati <fortunati.luigi@gmail.com> - 2026-02-12 23:26 -0800
    Re: Elastic Collision Mikko <mikko.levanto@iki.fi> - 2026-02-13 18:05 -0800
    Re: Elastic Collision kaukasoina3dore73js4@sci.fi (Petri Kaukasoina) - 2026-02-13 18:05 -0800
    Re: Elastic Collision pa@see.signature.invalid (Pierre Asselin) - 2026-02-13 18:05 -0800
    Re: Elastic Collision Luigi Fortunati <fortunati.luigi@gmail.com> - 2026-02-14 23:52 -0800
  Re: Elastic Collision "Jonathan Thornburg [remove -color to reply]" <dr.j.thornburg@gmail-pink.com> - 2026-02-15 00:26 -0800
  Re: Elastic Collision "Jonathan Thornburg [remove -color to reply]" <dr.j.thornburg@gmail-pink.com> - 2026-02-15 11:02 -0800
  Re: Elastic Collision Luigi Fortunati <fortunati.luigi@gmail.com> - 2026-02-16 17:14 -0800
    Re: Elastic Collision Luigi Fortunati <fortunati.luigi@gmail.com> - 2026-02-28 00:48 -0800
    Re: Elastic Collision Mikko <mikko.levanto@iki.fi> - 2026-02-28 10:43 -0800
    Re: Elastic Collision Luigi Fortunati <fortunati.luigi@gmail.com> - 2026-03-05 21:25 -0800
    Re: Elastic Collision Mikko <mikko.levanto@iki.fi> - 2026-03-07 23:16 -0800
    Re: Elastic Collision Luigi Fortunati <fortunati.luigi@gmail.com> - 2026-03-12 14:55 -0700
    Re: Elastic Collision Mikko <mikko.levanto@iki.fi> - 2026-03-15 23:32 -0700

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