- #1

sankalpmittal

- 785

- 15

From textbook : The book is at rest with respect to Earth - when the book is kept on the stationary table. The a^{→}of book with respect to Earth is 0. The forces acting on book are :

(i.) The gravitational force W exerted by Earth on book

(ii.) the contact force N by table

Is sum of W and N 0 ?A very accurate measurement will give the answer "NO " ! The sum of two forces ain't 0 although book is at rest w.r.t. earth. Earth is not strictly an inertial frame.However sum of W and N is not too different from zero and we can say that Earth can be assumed as an inertial frame of reference to a good approximation. Thus for routine affairs , "a^{→}= 0 if and only if F^{→}=0" is true in Earth frame of reference. This fact was identified and formulated by Newton i.e. Newton's first law of motion. If we restrict that all measurement will be made from the Earth frame , indeed it becomes a law. If we try to universalize this to different frames , it becomes a definition. We shall assume that unless stated otherwise we are working from an inertial frame of reference.

Now I can't understand that how come acceleration of book with respect to Earth isn't 0 ?! Please see bold part of quote above. Also please provide an intuitive understanding of frame of reference. Also , please explain the quote a bit more comprehensively.

Thanks in advace.

:)