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In message <34CC6849.9380FB3@novagate.com> Sargent Schutt writes:
> Phil Payne wrote:
> > In message <34CBEB4D.B0BB2005@novagate.com> Sargent Schutt writes:
> > > 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.
> > No - almost completely wrong.
> > And, if velocity is constant, acceleration _MUST_ be zero.
> > Think again of the bungee jumper - his BDC (zero velocity) is the moment of
> > _maximum_ acceleration. The rope exerts its greatest force when it is fully
> > stretched (Hook's Law).
> BDC would be the moment of zero acceleration. In the moment *immediately*
> preceeding and following would be his maximum acceleration. There is an instant
> in time when velocity, and therefore acceleration are zero.
There's your problem - there is no such link.
In the case of the velocity of the piston - it changes direction. Expressed in
any units, the sign changes and there is therefore a point at which the graph
crosses the X axis. At this point, velocity _is_ zero.
There is no such change (at TDC/BDC, anyway) in acceleration - the sign doesn't
change as slowing in one direction gives way to speeding up in the other, and
thus the graph doesn't cross the X axis and there's no instantaneous zero.
Committee Member, UK Audi [ur-]quattro Owners Club