Relativity and newtonian mechanics

the principles of newtonian mech. were built on the idea that one can measure time, length, and mass accurately and uniquely when describing the changing motion of an object. Must we select newtonian mech. now that we have learned that measurements of time, length, and mass vary from one observer to another? The answer is yes, if we are talking about objects that move near the speed of light. But at speeds of normal living, the relativistic changes of time, length, and mass are infinitesimal. A person's mass increases by less than a factor of 10^-13 when the person's speed increases from zero to 100m/s. Consequently, we can ignore this mass change whe using new. Mech. To analyze the person's motion. As a rough rule of thumb, we can usually ignore relativistic changes in mass, time, and length when the speeds of objects as moving reference frames are less than about one-tenth the speed of light. At this speed (v=0.1c) the factor [1 - (v^2/c^2)] ^1/2 that appears in the equations for time dilation, length contraction, and mass change equals 0.995. Thus, at v=0.12 there is only a 0.5 percent change in a time interval, length, or mass. At lower speeds the changes are even smaller, and the equations of new.Mech. Provide an adequate description of nature.