Path: ...!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail From: Luigi Fortunati Newsgroups: sci.physics.research Subject: Inertia and third principle Date: Sat, 22 Jun 2024 02:16:01 PDT Organization: A noiseless patient Spider Lines: 43 Approved: Jonathan Thornburg [remove -color to reply]" Reply-To: fortunati.luigi@gmail.com X-Trace: individual.net SK+iJfYnclO/8q1vDt/dhQyG+VnLiFgXs+hfLk+0pDg0nL5ZeHvQKkSMJI Cancel-Lock: sha1:q4nCbahYHE3Xno3g4UEaXz90Ajk= sha256:B6DdEHepxzR43iF0LSy36V6Qdwyph2Y+lf8tPixskMM= X-Forwarded-Encrypted: i=2; AJvYcCVSFiFQQVLfjoKIctW8JRrtjnNV0mwa8cT8PqaB+LVUIbo+xNRQ9Vwxuti7X+jKzEqMxE3uDs9afER2rpUbrS/2ZA916hoGJdQ= X-ICQ: 1931503972 X-Auth-Sender: U2FsdGVkX18U5R+g+YDicc3Uu+a0jxGAd1Ed1eJk9V2B7QbSGAzGy2wT6p++uwCl Bytes: 3056 In my animation https://www.geogebra.org/m/gxqwmxah at the moment of the collision the F1 and F2 forces of action and reaction between the two bodies A and B are activated. Is it true that force F1 is the sum of the blue forces of the particles of body A and force F2 is the sum of the red forces of the particles of body B? Could the forces F1 and F2 exist if the blue and red forces of the particles of bodies A and B did not exist? Luigi Fortunati [[Mod. note -- At the moment of collision, the only impact forces are those on the parts of the bodies which are in contact (labelled as points A and B in your very nice animamation). These then propagate pressure waves into the bodies, which apply forces on the rest of the bodies. So, the small red and blue arrows which your (very nice!) animation shows as being applied to each mass point of bodies A and B at the moment of collision are wrong -- the actual forces are very non-uniform across each body (as well as being highly time-dependent). Here's an article with actual data of this sort: Ross, Patel, and Wenzel "Vehicle Design and the Physics of Traffic Safety" Physics Today vol 49 (Jan 2006), pages 49-54 The /Physics Today/ article is behind a paywall, but as of a few minutes ago google scholar says there's a free copy at https://people.cas.uab.edu/~nordlund/Courses/PH201/Links/vol59no1p49_54.pdf The article has two graphs showing velocity as a function of time for various parts of cars during car crashes. You can clearly see how different parts of a car have different velocity profiles, and hence different accelerations. But, I think the answer to your first question may still be "yes". After all, ultimately the net force on body A is the sum of all the forces on A's individual mass points, and similarly for B. As for your second question, suppose that instead of two solid bodies, you just had a pair of clouds of dust moving towards each other. Then they'd interpenetrate and basically go right through each other, so the "impact" forces F1 and F2 would both be zero. -- jt]]