It is the only way in which the system momentum can be conserved. In the
Newtonian scheme this must happen because, no matter what the materials or
other details of the interaction, the mutual forces between the objects are
equal in magnitude and oppositely directed at each instant - this mandates
equal and opposite impulses and momentum changes, ie, conservation of system
momentum.
Thus: mv = (m + m) U => the final common speed is U = v/2, so that the
final system KE is
0.5 (2m) U^2 = 0.5 (2m)v^2/4 = (.5 m v^2) /2
= 1/2 the original KE
Newton's laws leave no room for any variations of this figure.
If no, or an "insufficient", dissipation mechanism is available, the
collision will not be totally inelastic and a common final velocity will not
be achieved. System momentum will still be conserved, but something less
than 1/2 the original KE will be dissipated - zero if there is no operable
dissipation mechanism (an elastic interaction).
Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net http://www.velocity.net/~trebor
----- Original Message -----
From: "David Abineri" <dabineri@CHOICE.NET>
To: <PHYS-L@lists.nau.edu>
Sent: Tuesday, November 26, 2002 10:43 PM
Subject: Loss of KE
| In an ideal inelastic collision (objects stick together) between two
| equal masses with one stationary initially, one half of the KE is lost
| (transferred to another form). Why is it that this amount of lost KE
| does not depend on the materials of which the objects are made? It would
| seem that one should get different results if they were made of steel vs
| foam rubber for example.
|
| Is this simply because this is an ideal situation or is there more to it
| than this?
|
| Thanks for any insights, David Abineri
|
|
|
| --
| David Abineri
| dabineri@choice.net
|
| This posting is the position of the writer, not that of SUNY-BSC, NAU or
the AAPT.
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