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From: zdenek@heathcliff.columbia.edu (Zdenek Radouch)
Newsgroups: sci.misc
Subject: freshman physics
Message-ID: <4087@columbia.UUCP>
Date: Thu, 11-Dec-86 15:12:47 EST
Article-I.D.: columbia.4087
Posted: Thu Dec 11 15:12:47 1986
Date-Received: Sat, 13-Dec-86 21:46:17 EST
Sender: nobody@columbia.UUCP
Reply-To: zdenek@heathcliff.columbia.edu.UUCP (Zdenek Radouch)
Organization: Columbia University CS Department
Lines: 19

>Consider the following thought experiment:
>
>	Take 2 identical cars and place them nose to nose.  Rig the 
>	accelerators of both so that you can give equal acceleration
>	to each.  Now slowly increase the accelerations of the two
>	cars.  Assuming that there is no slippage of the wheels, the
>	cars will remain motionless....

Note that if the cars are nose to nose (or as you pointed out motionless)
you cannot "slowly increase the acceleration". They are not moving let alone
accelerating. If there was no slippage of the wheels the engine couldn't run.
You have to take care of conservation of energy even in a thought experiment.
The work output of the engine can't just disappear. The cars are not moving
so the energy delivered by the engine has to go somewhere else. The wheels
must slip but the car will be motionless because the forces are balanced.

zdenek

 zdenek@cs.columbia.edu  or 	...!seismo!columbia!cs!zdenek