YES NOPE9 wrote:
> I looked at this on intergoogle and while there were some example  
> diagrams, I did not get a sense of what a rule of thumb for  
> determining the mechanical advantage of pulleys.
>   
The rule is: Count the number of lengths of the rope that are carrying 
the load and that
 number is the mechanical advantage.
> Assume the rope and pulleys have zero mass and no friction.
> Assume that I weigh 100 grams.
>
> I attach myself to the floor and pull on a rope that goes over a  
> pulley ( attached to the ceiling ) and has has an object attached to  
> it.  The object is gravitationally attracted to the ground with a  
> force of one newton.
>             I have to pull with a force of 1 newton to lift the  
> weight .... correct ?
>
>   
Yes! One section of the rope is carrying the load thus the mechanical 
advantage is 1 and  you
must exert 1 newton to lift a 1 newton weight off the floor.
> Now I detach myself from the floor and move the rope to a hook at the  
> top of my head.  Now I have to pull with a force of .5 newtons to lift  
> myself.  .... correct ?
>   

Can't picture this!

>
> Next I attach a rope to my head , run it up through side A of a double  
> pulley ( attached to the ceiling ) , back down to a pulley attached to  
> my head , back up through side B of the double pulley and back down to  
> my hands.   I have to pull with a force of .25 newtons to raise  
> myself ........  correct ?
>   
Can't picture this but the rule applies.
For a double block there are 2 lengths supporting the load so the 
mechanical advantage is 2
therefore you must exert 0.5 newtons to lift a 1 newton but you will 
spool off twice as much rope
as with a single block.

I think I remembered my physics class lecture on that more than 50 years 
ago <GRIN>

Vic

Vic Fraenckel
KC2GUI
windswaytoo ATSIGN gmail DOT com

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist