# Conrod force/acceleration

```Hi guys,

I'm still not able to receive email, but I can send email out.
SO, I've been monitoring the Q-list by reading the archives.

I thought I'd try to clear up Glen's misunderstanding of the
piston/conrod acceleration/force.

After reading a couple messages beyond the first one, it becomes
clear to me that Glen thinks the original formula that Orin quoted
calculates piston acceleration.   The formula calculates conrod _force_,
which is a maximum at TDC.   Just to be perfectly clear, this is the force
of the piston and crank on the conrod, trying to stretch it apart.

Glen said...

> Conceptually, I find it difficult to understand how acceleration is greatest
> at TDC, as the piston stops moving up, is momentarily motionless, and
> the starts to accelerate downward. How can acceleration be greatest at the
> instant in time that upward motion has ceased, the piston is motionless
> and then downward acceleration commences? It seems to me that acceleration
> must do to zero at some point as the piston approaches its point of zero
> motion.
>
> Guessing here again, and mebbe this is where my logic falls apart, I
> would think that
> max piston velocity would occur at mid-stroke and that acceleration would
> be zero at mid-stroke?

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.

HTH

Later,
Graydon D. Stuckey
810 733 0255 home
810 236 0783 work

```