"Harry K" wrote in message
m...
(Harry K) wrote in message
. com...
"Greg O" wrote in message
...
Harry,
Is this drawing, really any differant from

20 20
\ /
\ /
\ /
\ /
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40

this one?


40
/ \
/ \
/ \
/ \
/ \
/ \
20 20

Greg

No they are not the same: If the load in No.1 is 40 the drawing is
correct. If the load in No.2 is 20 the drawing is incorrect. In no.2
with load 20 the pull on the top will be 20 not 40.
See my experiment that I used to confirm the theory. It confirms what
I just said.

Harry K


A better explanation.

Diagram 2 is a class 1 pulley. It only changes the direction of pull
and does nothing to change the strain. If you were to tie off the
left line at the top (hook) what will the strain on the hook be?
Answer: 20 lbs, not 40. The 20lbs you are showing on the right leg is
only the same 20 lbs extended to a different anchor, not an additonal
20 lbs.

Diagram 1 is a class 2 pulley. It halves the load between two lines
but requires, say, 10ft of rope pull to lift the load 5 ft.

Harry K

Harry, when it comes to the forces seen at the three differant points in the
two drawings it makes no differance! Even though the drawnings are inverted,
they are essentially the same as far as the forces are concerned. Class 1,
or class 2 pulley has really nothing to do with it!
Greg