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In message <199801241903.LAA13062@gonzo.wolfenet.com> Orin Eman writes:
> > 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.
> Unfortunately, in this case, we have to take direction into consideration.
Well, we should really drift off into calculus.
However, to assist visualisation, think of a bungee jump.
A person jumps, and is accelerated towards the ground by gravity. The
rope comes tight, and starts to stretch - exerting an increasing force
that starts to exert a decellerating effect.
There is an instant at which the jumper is stationary, before being
dragged back up by the rope. The force being exerted on the jumper
is _greatest_ at this very instant, when the rope is at maximum
stretch. Since the mass of the jumper doesn't change (excepting
inadvertent egestion) the acceleration (product of force acting on
a mass) is also greatest at this instant.
It's exactly the same in a car engine - the acceleration is greatest
when motion drops to zero. Practically, it means that this is the
instant when the crank/connecting rod/piston are under the greatest
strain - any tolerances in the big and little end bearings will
cause the piston to move even further into the danger area.
Actually, piston movement in a car is sinusoidal. I failed A-level
maths thirty years ago, but ISTR that the result of differentiating
a sine curve is to shift it 90 degrees?
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