ericmazur / PnPbook

Tracking of typos, errors, and improvements for "The Principles and Practice of Physics"
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inertia versus mass distinction ... or not #134

Open JohnDenker opened 8 years ago

JohnDenker commented 8 years ago

See item #107 for a catalog of related issues.

Throughout the book, there is an alleged distinction between mass and inertia. In the early chapters, in non-relativistic situations, this is a distinction without a difference ... but the intent becomes clear in connection with special relativity, culminating in equation 14.41 in section 14.7 on page 367.

Alas, equation 14.41 cannot be correct. It is ruled out by experiments, including Eötvös experiments, with many orders of magnitude to spare. More generally, the distinction between mass and inertia is inconsistent with the weak equivalence principle, as set forth on page 321.

Remark: There was a period in history when experts thought that special relativity could be explained with the help of velocity-dependent mass, but that only lasted a couple of years, and it was more than 100 years ago. It never really worked; there were proposals for "longitudinal" mass, "transverse" mass, "electromagnetic" mass, and who-knows-what else.

Suggestions:

Sometimes factors of γ appear in the equations of motion. Although sometimes they belong there, in many cases they can be and should be eliminated. The solution is never to rewrite the equation using a worse definition of mass; in most case the solution is to rewrite the equation using a better definition of time, i.e. proper time.

References:

  1. Misner / Thorne / Wheeler Gravitation Nominally this is a book on general relativity, but it starts out with a clear, clean, modern exposition of special relativity.
  2. "Welcome to Spacetime" https://www.av8n.com/physics/spacetime-welcome.htm
  3. "Velocity and Acceleration in Spacetime" https://www.av8n.com/physics/spacetime-acceleration.htm
  4. See item #201 for a catalog of items related to special relativity; see item #199 in particular.