That's not connecting the dots, that's just repeating the same things you've been saying over and over again.

Originally Posted By: paul

the two forces cancel each other out


I agree the forces are of equal magnitude and opposite direction. But they're applied at different times. The sequence of turnaround forces to the pipe might look like this. I've ignored the accelerator for now -

+1 1st turn
-1 2nd turn
+2 1st turn
-2 2nd turn
+3 1st turn
-3 2nd turn
...

Since this is a continuous process, there's no reason we have to group 1st and 2nd turns together. We could group each 2nd turn and its following 1st turn together:

-1 2nd turn
+2 1st turn

-2 2nd turn
+3 1st turn

-3 2nd turn
+4 1st turn

Just by putting spaces between the lines, suddenly they no longer cancel each other out!


How about we include the accelerator:

-1 accelerator.
+1 1st turn.
-1 2nd turn.
-1 accelerator.
+2 1st turn.
-2 2nd turn.
-1 accelerator.
+3 1st turn.
-3 2nd turn.

Looks like unbalanced force because each group of three adds up to -1. But write them out in blocks of the same sequence, just grouped into blocks:

-1 2nd turn.
-1 accelerator.
+2 1st turn.

-2 2nd turn.
-1 accelerator.
+3 1st turn.


Clearly each set of 2nd turn, acceleration, 1st turn produces zero total force. They all cancel out!!!

All this is very rough, but it clearly shows that just having the same force at both ends doesn't mean you can ignore them.

Fundamental reason: They don't occur at the same time as each other. Even if you add more masses they can't consistently occur at the same time, try drawing an animation if you don't believe me.