If instead of simply putting the rope through the last loop, he made another pulley-loop and then went back around the tree, would he multiply his force yet again?

That's great... as long as you've got a post or tree nearby.

Sue

Probably, at least in theory. Should really increase the friction too. If you are going to rely on this, I would suggest buying some real pulleys, and a short section of rope/strap to secure one to the tree with...

I agree with having real pulleys, but I'm trying to find out what the possibilities are with just a rope. You may find yourself in a situation with only a rope to pull a car out of the mud.

"...with only a rope..."

In that case, rig this thing up, and good luck...

the army does it like this:

http://www.globalsecurity.org/military/library/policy/army/fm/3-97-61/ch7.htm#fig7-26

WARNING-WARNING-DANGER-DANGER

Under any serious load, the moving part of a nylon rope will very quicky melt/saw right through the stationary loop it is running on. Run the rope over a metal carabiner instead.

He has basically created a 3:1 Z-rig without the use of pulleys. The system will work for short distances, but as already noted, there is loss of mechanical advantage due to the rope on rope friction.

Rope on rope is not ideal, but we utilize this method when creating static back-ties on questionable anchor points such as small trees, poles, etc. We tie the back-tie line (high up, as well as the main or belay line – generally you keep you anchor points low to create sheer force instead of lever force, but when back-tying high, the vector forces will be directed downward) to the tree/pole, place a butterfly knot in the line about ½ back and then run the line around the base of a smooth, but sturdy tree/pole and take the running end back through the butterfly, thus creating a 2:1 mechanical advantage.

Pete