> >> To make this very simple terms. =A0Take the number of ropes attached t=
o to
> >> the MOVEABLE pulleys divide that into the weight being lifted =A0and t=
hat
> >> is the force required to lift the object.
> >
> > As long as all ropes are vertical :-)
>
> Well, only if it is lifting a free hanging mass.
>
> But the principle is exactly the same for a block and tackle pulling
> something up an incline, all the rope lengths going to the moving mass are
> under equal tension.

E&OE :-) ...

My point (not being quoted above) about ripes being vertical is that
ropes can be at an angle to the resisting force field so that only a
component of the rope tension supports or pulls the load. Such cases
complicate the simple examples for beginners.

eg -  2 horse pull a cart up a ramp by a rope fastened to a pulling
collar on each horse and passing through a single pulley in the front
middle of the cart. The horses are 6 feet apart and the pulling collar
attachment s are 10 feet in front of the cart.

If the drawbar pull on the cart is say 200 lbf the rope tension will
NOT be 200/2 =3D 100 lbf.
The up slope component will be 100 lbf but rope tension will be
sqrt(100+9)/10 x 100 lbf =3D 104 lbf.
Hardly any difference.
But if the horses were 10 feet apart it becomes sqrt(125)/10*100 =3D 112 lb=
f.
When/if the ropes get out to 45 degrees either side rope tension is
141 (100 x sqrt(2) lbf.
All the increase comes from pulling at an angle so that only a
component applies.

This increase has nothing to do with pulleys per se but can be
introduced into examples to complicate them without people being very
aware that it has happened.

As long as the ropes ascend vertically from YesNopeGus's head all is well.

                R

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