# RE: interference fit

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All OK too. Just to make terms easier, acceleration, in either direction
is still acceleration, or increasing velocity over time. Deceleration is
slowing down, reducing velocity over time, direction of motion up or
down is irrelevant.

-glen

> OK, I see your point but I'm still not clear on it. I think of it (prolly wrong) this way:

> The piston is moving up toward TDC.
> At some instant in time it will be at rest at TDC.
> For it to achieve the state of rest or 'no motion' the piston must decelerate to 0.

All true.

Most of the confusion comes with the terms 'acceleration' and
'deceleration'.  Direction is important...

Taking 'upwards', ie. towards TDC as positive, then an increase
in speed towards TDC is a positive acceleration, a decrease in
speed towards TDC is a _negative_ acceleration (or deceleration).

As the piston approaches TDC, its speed towards TDC is decreasing,
so we have negative acceleration.  After the piston passes TDC,
its speed is increasing downwards, ie. it is still a _negative_
acceleration given our frame of reference... the sign of the
acceleration never changes as the piston passes TDC.

Somewhere around 90 deg after TDC, the piston will reach its
maximum speed (where 'around' is a pretty broad term here)
and start slowing down.  This is a point of zero acceleration.
as is the point to the point of maximum speed on the next
upwards stroke.

It is counter-intuitive...

I'll look up the formulae tonight.

Orin.

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