Inlerf -
glad the link helped...
I'll have to beg to differ about your assesment of your drawing - it *does* look realistic - just not *photo-realistic*...
It can be frustrating - but you have to remember that graphite and charcoal and paper are different mediums than photography - you can do different things,they have different strengths and weaknesses,
I think maybe you are thinking about the skills of master draw-ers? What do they do that you aren't? Well, practice for one - but also an understanding of anatomy, perspective and using shadows to portray weight, volume and pressure, and expressiveness in line quality... but mostly they know the strengths of their medium and play to them...
These are things that take practice.
Save the perspective and anatomy lessons for later. You have a pretty good sense of that (and based on your physics notes, I don't think it'll blow your mind thinking about it

). For now I recommend practicing with light and shadows - I think you'll find that thinking about reflected light and volume will help your renderings.
Other things that will help with expressive line quality are experimenting with different weights of line and varying the quality of edges (you have done this well, and instinctively in your last drawing - note the differences between edge quality on Willow's forehead vs her eye lid)... a place where pressing harder or lighter on your pencil (or using different quality of line) might have given your drawing some more dynamics is around the mouth area (where it makes sense to be dynamic).
An exersize that might help with that is contour drawing excersizes - I especially like blind countour drawings for this, but not everyone can wrap their mind around that (plus you kinda need big pieces of paper)
Your drawings are really good - you are doing a number of things really well! There are lots of factors to take into consideration in a drawing and you are doing most instinctively... at any rate you should definately keep it up. Keep drawing! You have lots of talent.
my two bits.
db