Variables

I am new to flash and I was reading about variable objects. Here is the code That I put on a movieclip to see if it would make the movie clip move.
onClipEvent (load) {
pos = {x:10, y:300};
}
onClipEvent (enterFrame) {
this.pos.x += 5;
trace(pos.x);
}

It works in the output window but moviclip does not move. I know there is a easier way to make it move i was just trying to understand about variable objcets I also attached a small file