var angle = 0;
var amplitude = 80;
var ang_velocity = 5;

var y = 0;
var x = 0;

moveTo(Stage.width/2 + amplitude, Stage.height/2);
lineStyle(2,0xFF0000,100);

onEnterFrame = function (){
x = Stage.width/2 + amplitude*Math.cos((angle*Math.PI)/180);
y = Stage.height/2 + amplitude*Math.sin((angle*Math.PI)/180);

angle += ang_velocity;
lineTo(x,y);
}