tag:blogger.com,1999:blog-4170372999716925583.post9011569862295456569..comments2016-11-28T03:56:43.773-08:00Comments on The Reflection of Physics: Newton's Law of MotionJC Sterlacehttp://www.blogger.com/profile/07148407440183898476noreply@blogger.comBlogger3125tag:blogger.com,1999:blog-4170372999716925583.post-40797008532307442102016-11-28T03:56:43.773-08:002016-11-28T03:56:43.773-08:00The first law defines the range of validity of the...The first law defines the range of validity of the second:<br />1st Law: There exist reference frames, which we call inertial reference frames, such that an object with no net force will move at a constant velocity.<br />2nd Law: In an inertial reference frame, F=dp/dt=ma.<br />3rd Law; For objects 1 and 2, if 1 exerts a force F_21 on object 2, then object 2 exerts a force F12=-F21 on object 1.<br /><br />The first law declares the existence of an infinite amount of inertial frames in which the second law is valid. Without the first law, the meaning of the equation ma=F is unclear. What is F? <br />You say you can discard the first law and keep only the second and you take forces to mean "an interaction between two objects". Assume you are in a reference frame in which there is body at rest. If you change to an accelerating reference frame, the body will start accelerating. According to your understanding of the second law (i.e. valid in every reference frame), there is a force acting on the object. If force is interaction between two objects, what is the second object interacting with our body? Filip Kostkahttp://www.blogger.com/profile/06425302180119761017noreply@blogger.comtag:blogger.com,1999:blog-4170372999716925583.post-29242329713380863472011-03-23T19:59:51.315-07:002011-03-23T19:59:51.315-07:00I wish I had read this before the Newton's Law...I wish I had read this before the Newton's Laws test!Oscarhttp://www.blogger.com/profile/17279683187484270984noreply@blogger.comtag:blogger.com,1999:blog-4170372999716925583.post-68916472773733087062010-12-29T04:18:55.834-08:002010-12-29T04:18:55.834-08:00Tremendous! I've been teaching my students th...Tremendous! I've been teaching my students that Newton's 1st Law is redundant, but hadn't made the connection to define a force as an interaction between two objects... which therefore allows you to pull in Newton's 3rd Law!Mr. Fhttp://www.blogger.com/profile/06688676870842430645noreply@blogger.com