# RE: interference fit

```Good Frank, I am getting closer to understanding, thanks.
However, still seems to me that deceleration must approach
zero as the piston approaches TDC and the piston does come
to a complete stop for an instant in time. It also seems to me that
at that instant in time after deceleration is complete and before
downward acceleration commences that there must be an instant
of zero deceleration coinciding with the instant of zero motion.
This assumption is why I cannot understand the previous assertion
"acceleration is highest at TDC" that started this thread. At the
instant of transition from upward deceleration to downward
acceleration and while the piston has no velocity at
the instant of time that it is at TDC how can this instant be the
point of maximum acceleration......?

Now if maximum acceleration is immediately before or after the instant
of TDC that makes more sense to me.....

-glen

acceleration means the speed is increasing.
deceleration means the speed is decreasing.
the fastest piston speeds occur near the halfway point of the stroke.
therefore, the piston accelerates from TDC to ~ halfway down, then
decelerates to zero at the bottom of the stroke, accelerates again until
~ halfway up and decelerates again until zero vertical displacement
occurs at TDC.

zero velocity occurs when change of displacement over time is zero.
zero acceleration occurs when change of velocity over time is zero.
if you make a graph of displacement and velocity of the piston over the
time period of a single engine rotation, these zero slopes are defined
wherever the curve is parallel to the time axis.  these also happen to be
the maximum and minimum points on a cyclic curve such as this.

frank

to: IN:gpowell@acacianet.com
cc: IN:quattro@coimbra.ans.net

```