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From: tll@druxu.UUCP (LaidigTL)
Newsgroups: net.auto
Subject: Re: 55 saves whot
Message-ID: <928@druxu.UUCP>
Date: Tue, 7-Feb-84 12:50:57 EST
Article-I.D.: druxu.928
Posted: Tue Feb  7 12:50:57 1984
Date-Received: Thu, 9-Feb-84 22:04:59 EST
References: <5465@decwrl.UUCP>
Organization: AT&T Information Systems Laboratories, Denver
Lines: 20

The article describing increased fuel use at higher speeds is generally
good, but it does overstate the increase.

	As for getting better mileage at 80 vs. 60, BUNK.  Drag goes up at the
	CUBE of velocity, so at 80 one would have to expend about 2.37 times
	as much fuel to overcome drag as one would at 60.  Internal friction
	in the engine is non-linear also, being somewhere near the square of
	the engine speed.  This implies about 1.78 time as much fuel.

Although it is true that drag goes up at the cube of velocity, this
means that energy needed PER UNIT TIME goes up as the cube of velocity.
Since distance covered per unit time goes up linearly with velocity
(How's that for an obvious statement?), energy needed per unit distance
covered only goes up as the square of velocity.  Similarly, energy per
unit distance to overcome internal friction only goes up linearly with
velocity.

			Tom Laidig
			AT&T Information Systems Laboratories, Denver
			...!ihnp4!druxu!tll