# Re: Conrod force/acceleration

```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. Just as there is
also an instant in time when velocity is constant positive (between pos/neg
accel) and acceleration is zero. Or are we just arguing semantics and the
definition of ZERO? Eg zero is so infinitely small as to not actually exist? I
think it does, - that's my understanding.

I'm more than willing to be corrected, just trying to figure out what we're
arguing here.  bungee jumper - at top of travel, he experiences a moment of
weightlessness, hits zero velocity for a moment, then plummets back toward the
earth. At the bottom of his travel, there is no weightless feeling b/c of
gravity, but there is still a moment of zero velocity, and therefore 0
acceleration. If a=*v/t, when *v=0, a=0. No? Or is there *never* an instant in
time when *v=0. Which are you suggesting? Enquiring minds want to know...

Sarge

```