Richard Harrison wrote:

Keith wrote:
"Why are you convinced the reflection point had to move?"

This is the case when a line is extended to greater length, and the
short or open also is moved to the new end of the line.

Ever had a short or open somewhere in the middle of a line?

Actually, no.

I have, and
can testify that the signal doesn`t get past a real hard short or open
in the line.
As energy can`t be destroyed it had to be reflected by the
hard short or open.

Or just stopped and stored, perhaps. This is certainly what happens
when you excite the line with a step function rather than a sinusoid.
When excited by a sinusoid, no energy moves at the quarter wave points
where the voltage or current is always 0. As you move away from the
quarter wave points, more and more energy moves on each cycle until
a maximum amount of energy is moved at the point half way between the
quarter wave points. And then it decreases back towards the next
quarter wave point.

All of this is easily visualized by observing the amplitude of the
p(t) function at various points along the line.

In the case where the line short is moved to a point nearer the source,
or where the short or open is moved to a place more distant on the line
from the source, we know the energy travels all the way to the actual
short or open where it is reflected because nulls occur at several
points along a long transmission line.

"we know" is rather strong. I would strongly suggest that no energy
crosses those points in the line where the voltage and current are
always zero since p(t) is always zero at these points.

If the energy were turned around
before it reached the end of the line, nulls more distant from the
source than the turnaround point would not exist.

Not so, the line has reached steady-state. Now the nulls exist. They
did not exist before the line reached steady-state.

There would be no
energy at the actual short or open at the end of the line were the
energy turned around before it reached the end of the line.

Not necessarily. Only once the line has been charged, does the energy
move back and forth between the quarter wave points, while not
crossing them.

Try visualizing how a step function charges the line. How the voltage
step propagates down the line. How the voltage step is reflected at the
open end and starts travelling back towards the start. How between
the start of the line and the returning voltage step, energy is
flowing to charge the line, but between the returning voltage step
and the open end of the line, the energy previously delivered is
statically stored in the capacitance of the line. How once the line
is completely charged, no current flows, there is no power, and
the energy delivered during charging is stored in the capacitance.

Sinusoidal excitation is more difficult to visualize, but the
prinicipal is the same.

....Keith