[img]http://2.bp.blogspot.com/-fKJMF7z908A/U0t2KnjvpxI/AAAAAAAABt0/ZhpYBUNw83M/s1600/ff.jpg[/img]

We speak about very important problem
RADIAL FORCES !!!

[b]first half [/b]
first half of the priod pendulum want to push the Earth  ( give Earth rotation )

[b]next half [/b]
pendulum want to push the Earth opposite to first half


IF EARTH TOOK  ENERGY FROM PENDULUM in FIRST HALF
PENDULUM CAN NOT PUSH EARTH IDEAL OPPOSITE TO FIRST HALF in NEXT HALF

pendulum will stop on planet even if not exist air friction and rope friction


EN > http://youtu.be/XWYFIUEaOmc  PL >http://youtu.be/rs8d1zBHgrw