Edgar wrote:
I particularly enjoyed his efforts to convince us that he could prove
by
trigonometry that a piston travelled further on the upstroke than the
downstroke (or maybe it was vice versa)
Edgar, sorry to burst your bubble, but this was one case where jaxie
was right! The piston travel from 90 degrees to 270 degrees is
different from 270 to 90 degrees. This is one of the "bar puzzles"
that is counter-intuitive, since we would normally think in terms of
upstroke versus downstroke, or 0-180 versus 180-0, which is quite
different from "top of cycle" versus "bottom of cycle." (I suppose it
depends on which bar you hang out in...)
At the risk of starting this thread again I do not think you are
correct.
The geometry of 90-270 is identical to that of 270-90 and so is 0-180
and
180-0.

Oh My! Jaxie hasn't posted here in over 2 years and he's still
catching people with this one!

The geometry is clearly not the same for the top and bottom parts of
the cycle. Draw it out - its just a matter of trig. The piston moves
slightly more than half its travel going from 0 (TDC) to 90 degrees.

As an interesting degenerate case, consider when the connecting rod is
the same length as the crank offset (I forget what that is really
called). In that case, the piston will reach the center of the crank
at 90 degrees and stay stationary for the entire bottom half of the cycle.

That is a situation impossible in practice.

Hmmm. Is it really impossible? I think you might be able to. But it
really doesn't matter, its just a degenerate case to show clearly that
the geometry is not symmetrical.

If you just draw it out with lines on paper you will find that the piston
does not move at all once it is at the centre since everything would just
revolve around it.

The problem in this case is that on the upstroke there is no force
that raises the piston. If, however, you made the con-rod a tad
longer then it would clearly show almost all of the travel in the top
half of the stroke.

I am beginning to think that you invented Jaxx just to have a bit of fun
with us...

I think we all play the game of inventing a "straw man" to argue with.
Republicans do it all the time by casting the typical Democrat as
an ultraliberal that in truth was only found with a few hundred yards
of Harvard or Berkeley for a few milliseconds about 40 years ago.
(Actually, every now and then I go to party where I encounter people
like that, but then I live only a few miles from Harvard Square.)

Jaxie was a living, breathing straw man that gave us all the
opportunity to know that we are at least smarter than one person.