var G:Number = 100;
 
function calcAcceleration(dot0:MovieClip, dot1:MovieClip):Point
{
	var r:Point = new Point(dot1.x - dot0.x, dot1.y - dot0.y);
	/*if (r.length < 14.5)
		return new Point(0, 0);*/
 
	var rSqr:Number = Math.pow(r.length, 2);
 
	r.normalize(G * dot1.m / rSqr);
 
	return r;
}
 
function normalizePositionVelocity(dot:MovieClip):void
{
	/*if (dot.x > 550)
		dot.v.x = -Math.abs(dot.v.x);
	if (dot.x < 0)
		dot.v.x = Math.abs(dot.v.x);
	if (dot.y > 400)
		dot.v.y = -Math.abs(dot.v.y);
	if (dot.y < 0)
		dot.v.y = Math.abs(dot.v.y);*/
}
 
function calcKineticEnergy(dot:MovieClip):Number
{
	return dot.m * Math.pow(dot.v.length, 2) / 2;
}
 
function calcPotentialEnergy(dot0:MovieClip, dot1:MovieClip):Number
{
	var r:Point = new Point(dot1.x - dot0.x, dot1.y - dot0.y);
	return -G * dot0.m * dot1.m / r.length;
}
 
addEventListener(Event.ENTER_FRAME, enterFrame)
function enterFrame(event:Event):void
{
	dot0.v = dot0.v.add(calcAcceleration(dot0, dot1));
	dot0.v = dot0.v.add(calcAcceleration(dot0, dot2));
	dot0.v = dot0.v.add(calcAcceleration(dot0, dot3));
	normalizePositionVelocity(dot0);
 
	dot1.v = dot1.v.add(calcAcceleration(dot1, dot0));
	dot1.v = dot1.v.add(calcAcceleration(dot1, dot2));
	dot1.v = dot1.v.add(calcAcceleration(dot1, dot3));
	normalizePositionVelocity(dot1);
 
	dot2.v = dot2.v.add(calcAcceleration(dot2, dot0));
	dot2.v = dot2.v.add(calcAcceleration(dot2, dot1));
	dot2.v = dot2.v.add(calcAcceleration(dot2, dot3));
	normalizePositionVelocity(dot2);
 
	dot3.v = dot3.v.add(calcAcceleration(dot3, dot0));
	dot3.v = dot3.v.add(calcAcceleration(dot3, dot1));
	dot3.v = dot3.v.add(calcAcceleration(dot3, dot2));
	normalizePositionVelocity(dot3);
 
	dot0.x += dot0.v.x;
	dot0.y += dot0.v.y;
 
	dot1.x += dot1.v.x;
	dot1.y += dot1.v.y;
 
	dot2.x += dot2.v.x;
	dot2.y += dot2.v.y;
 
	dot3.x += dot3.v.x;
	dot3.y += dot3.v.y;
 
	empty.graphics.lineStyle(1, 0x333333);
	empty.graphics.lineTo(dot0.x, dot0.y);
 
	var kineticEnergy = calcKineticEnergy(dot0)
		+ calcKineticEnergy(dot1)
		+ calcKineticEnergy(dot2)
		+ calcKineticEnergy(dot3);
 
	var potentialEnergy = calcPotentialEnergy(dot0, dot1)
		+ calcPotentialEnergy(dot0, dot2)
		+ calcPotentialEnergy(dot0, dot3)
		+ calcPotentialEnergy(dot1, dot2)
		+ calcPotentialEnergy(dot1, dot3)
		+ calcPotentialEnergy(dot2, dot3);
 
	kinE.text = new String(kineticEnergy);
	potE.text = new String(potentialEnergy);
 
	e.text = new String(kineticEnergy + potentialEnergy);
}