User talk:Vivers

Newton's second law
Hi. I reverted this edit because neither F = ma nor F = dp/dt apply directly to variable-mass systems. This is treated briefly at Newton's laws of motion. It has also been the subject of extensive discussions on the talk page: Talk:Newton's laws of motion; Talk:Newton's laws of motion. Strad (talk) 17:29, 15 August 2009 (UTC)

Yes, I understand now. I was recalling a lecture by an engineering professor where he solved an example of a rocket ejecting propellant and used the product rule on F=d(mv)/dt. Evidently, he misunderstood, or more likely, miscommunicated. Halliday/Resnick has an excellent derivation (Third Edition, Section 9-7, pp. 174-179) which gives a more thorough treatment of the variable mass problem. Getting the full derivation into Wikipedia would help. Perhaps as an article in its own right? That leaves this article as a general intro and the new article for those who need to dive deeper. Other articles would be benefit by a separate treatment of the subjects. For example, Force may reinforce the product rule approach and needs to be corrected? Vic (talk) 12:17, 17 August 2009 (UTC)