John M wrote:
| The fact that that object *appears* to another observer to
| asymptotically approach the speed of light is the *observer's*
| problem!
Whatever this means, is it not in the same way the "object's" problem that
the left behind observer "appears" to asymptotically approach the speed of
light?
We understand that speed is a relative quantity and that the idea of an
"intrinsic" speed is without meaning or use. So what's the point?
Bob Sciamanda
Physics, Edinboro Univ of PA (Em) http://www.winbeam.com/~trebor/
trebor@winbeam.com
----- Original Message -----
From: "John Mallinckrodt" <ajm@csupomona.edu>
To: "Forum for Physics Educators" <phys-l@carnot.physics.buffalo.edu>
Sent: Tuesday, February 21, 2006 2:30 PM
Subject: Re: [Phys-l] geometry of spacetime (was: relativisitic mass ...)
| >The problem I have with relativistic mass is that conceptual level texts
use
| >it to explain why it is more difficult to accelerate an object when it is
| >traveling at high speeds. Unfortunately, they are implicitly using an
F=ma
| >approach - which means that they are actually talking about the old
| >"longitudinal" mass (a 3/2 power) - not the relativistic mass (a 1/2
power
| >of 1-v^2/c^2). Invariant mass and the use of F=dp/dt avoids this.
|
| Not that I disagree with the thrust of these comments, but as a side
| note I would offer my opinion that we also needlessly confuse matters
| by saying things like "it is more difficult to accelerate an object
| when it is traveling at high speeds" for the simple reason that
| objects do not *intrinsically* "travel at" any--let alone
| high--"speed" and, therefore, do not become "more difficult to
| accelerate."
|
| It should be very well understood that an object can, in principle,
| experience an arbitrarily large, constant acceleration for an
| arbitrarily large amount of time. It can do so by firing its
| thrusters at a constant level of thrust.
|
| The fact that that object *appears* to another observer to
| asymptotically approach the speed of light is the *observer's*
| problem!
|
| --
| John "Slo" Mallinckrodt
|
| Professor of Physics, Cal Poly Pomona
| <http://www.csupomona.edu/~ajm>
|
| and
|
| Lead Guitarist, Out-Laws of Physics
| <http://www.csupomona.edu/~hsleff/OoPs.html>
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