Algodoo

This one boggles my mind! I don't understand how this works because it appears that the diameter of the pulley doesn't change, and it rotates on the same central point regardless of the changing configuration of those articulated levers that are behind the pulley. So WHAT is it that produces the constant force on the left rope? Could you elaborate on this?

Thanks

It's like automatically changing the pivot point of a see saw to accommodate the weight of the riders. I suspect that the pulley mechanism is doing some work since the change in potential energy of the right spring is greater than the force times distance on the left rope.

That's really amaizing!

"It's like automatically changing the pivot point of a see saw to accommodate the weight of the riders."

I still don't see HOW it works. When I look at the pulley and ignore the changing mechanism behind it, I see two separate ropes that are attached to the circumference of a pulley. As I press the up and down arrow keys, I see the mechanism moving, but I don't see what changes on the pulley that would make a mechanical difference between the right rope and the left rope. The pulley doesn't seem to change size, and the pivot point remains exactly in the center. I am not seeing something that would explain how this works. In your previous scene, it was quite obvious.

S: When I ... ignore the changing mechanism.
R: Don't do that.

S: The pivot point remains exactly in the center.
R: While it's true that the pulley rotates about its center, the hinge that balances the left and right forces moves horizontally with respect to the ground.

The scene employs two robot arms, one arm is attached to ground and positions the pivot hinge to balance the right and left forces. The other arm is attached to the pulley and maintains the pulley location. The two arms are connected to each other with a freely rotating hinge.

Hopefully the explanation above helps out. If not, then you might be out of luck because I'm not sure if I understand it completely.

Other users should feel free to offer an explanation.

Now I think I understand it. The part that threw me was your statement: " It does this by shifting the pulley pivot point while maintaining the pulley in the same location." For some reason I thought that the center point of the pulley rotates via an axle that is fixed to the background. If that were the case, then your statement would be self-contradictory! But now I realize that the pulley is "floating" freely on the end of an articulated balance beam which has a variable position "virtual" fulcrum. By changing the positions of the articulated joints, the position of the variable fulcrum shifts left or right while maintaining the pulley's central rotation point. The position of the fulcrum determines the loading effect on the pulley, which determines the force that's seen by the rope.

These are my own words, and this is how I think this device works.

Good explanation. I couldn't have said it better.