How to find the fulcrum of the moving pulley (lever)?

Moving pulley, now assume that the rope on the right side of the moving pulley is fixed and the weight W hangs on the shaft of the moving pulley.

Now pull up the rope on the left side of the pulley and force F.

At this time, it is equivalent to the right rope as the fulcrum, and the weight is downward in the center direction of the pulley, which is equivalent to the distance from the right fulcrum as the pulley radius r;

The pulling force f of the left rope is upward, and the distance from the right fulcrum is the pulley diameter 2R.

Then: F*(2R)=W*R

F= 1/2W

This is the labor-saving function of the moving pulley (equivalent to the labor-saving function of the lever);

When the weight is lifted by S distance, the right rope end is fixed, which is equivalent to the left rope being pulled by 2S distance. (This is also equivalent to the scope of the lever)

F*2S=W*S-moving pulley saves effort, which is equivalent to lever saving effort.