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# Re: Conrod force/acceleration

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Olesen, Allan wrote:

> On Sat, 24 Jan 1998 09:48:52 -0500 (EST), you wrote:
>
> >Glen, your assumptions are correct, as you write them.
> >_Acceleration_ of the piston is zero at TDC as is velocity, relative to
> >the engine block.
>
> Wrong.
>
> If both acceleration and velocity are 0 at the same time, it is a
> clear indication that the engine isn't running at all.

Come again? Is there not a point in time where acceleration and velocity
are zero? I certainly think so. When there is no velocity, there is no
acceleration. Acceleration can be zero while velocity is constant, but if
velocity = 0, acceleration = 0; acceleration is nothing more than the rate
of change in velocity. At TDC velocity is zero, and therefore acceleration
is zero, too. Yet the engine is most definitely running.

> And to Glen Powell:
> You have to understand that "upwards deceleration" is exactly the same
> as downward acceleration. Consequently, the transition from upwards
> deceleration to downward acceleration, that you have mentioned
> earlier, does not take place.

Are you suggesting a perfectly parabolic acceleration curve with no zero
point? (1) There will be a time when acceleration is zero; (2) You have
massive acceleration/deceleration approaching/leaving TDC, as a function of
rapid reversal of travel. You also have zero velocity, and therefore zero
acceleration, at one micor-instant in time (at TDC).

Additional question: additional cylinders = more rapid acceleration, more
constant crank velocity, lower piston velocity overall? Eg in a I-4 vs. I-5
vs. V8 vs. V12?

Sarge

91 200q
86 5ktq

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