Subject: Voltage, what exactly is it?

 Hello, my name is Kaare Mikkelsen, I'm presently attending a Danish Gymnasium
(much like highschool) in the 12th grade, the math/hysics line.
  I apologise if I do no use the proper terminology below, I hope I still get 
the thoughts across.
 I've been explained into numbness what, in general, U, I and R means. R is 
resistance (how "difficult it is for the current of electrons to pass through 
a given media), I is the "proportions" of the current compared to the time, 
and U is how much energy the current "deposits" in the media compared to 
the "size" of the current. I also know that if there is no difference in 
charge between two points then no electrical current can run between these two 
as an elecetrical current is really just charge moving to become "evenly 
spread". 
  But what makes U higher for some currents than others? What is the 
difference between an electron "depisiting" x energy and one depositing 2x? Is 
it the speed with whic it travels, or something?

Re: Voltage, what exactly is it?