Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/5/84; site mnetor.UUCP Path: utzoo!utcs!mnetor!fred From: fred@mnetor.UUCP (Fred Williams) Newsgroups: net.physics Subject: Re: Newton's Second Law Message-ID: <1182@mnetor.UUCP> Date: Fri, 5-Jul-85 09:56:34 EDT Article-I.D.: mnetor.1182 Posted: Fri Jul 5 09:56:34 1985 Date-Received: Fri, 5-Jul-85 11:10:07 EDT References: <9255@Glacier.ARPA> Reply-To: fred@mnetor.UUCP (Fred Williams) Distribution: net Organization: Computer X (CANADA) Ltd., Toronto, Ontario, Canada Lines: 26 Summary: In article <9255@Glacier.ARPA> wong@Glacier.ARPA (Man Wong) writes: >What is the content of Newton's Second Law? Is it a definition? Can definitions >be called physical laws? > >Please help! Newton's second law really defines a relationship between mass, force, and the "time rate of change of momentum". I believe Newton himself expressed it as; dp F = ---- dt It is interesting to note that this holds true even when relativistic effects are taken into account. It resolves to "ma" when the mass is constant. I do not mean to imply that Newton anticipated Einstein, merely that he knew well the calculus which he invented and it's implications in the real world. If you are looking for the definitions of "mass" and "force", check any good physics text. Cheers, Fred Williams