decreasing E while swinging a rope.

[gelatine]

hello can someone tell me a site where i can read something about E (energy from physics) that goes down by friction and air resistance. i need it for a program about a rope swinging. A quick reminder for anyone who does not know what i mean with E:
E=m*g*h + m*0.5*pow(v,2)
or E=potential energy+kynetic energy;