Attractor.prototype.calculateAttraction = function(m) {
var force = PVector.sub(this.position, m.position);
var distance = force.mag();
distance = constrain(distance, 5, 25);
force.normalize();
var strength = (this.G * this.mass * m.mass) / (distance * distance);
force.mult(strength);
return force;
};

Attractor.prototype.display = function() {
ellipseMode(CENTER);
strokeWeight(4);
stroke(0);
ellipse(this.position.x, this.position.y, this.mass*2, this.mass*2);
};

var Mover = function(mass, x, y) {
this.position = new PVector(x, y);
this.velocity = new PVector(1, 0);
this.acceleration = new PVector(0, 0);
this.mass = mass;
};

Mover.prototype.applyForce = function(force) {
var f = PVector.div(force,this.mass);
this.acceleration.add(f);
};

Mover.prototype.update = function() {
this.velocity.add(this.acceleration);
this.position.add(this.velocity);
this.acceleration.mult(0);
};

Mover.prototype.display = function() {
noStroke();
fill(0, 0, 0, 50);
ellipse(this.position.x, this.position.y, this.mass*16, this.mass*16);
};

var movers = [];
var attractor = new Attractor();

for (var i = 0; i < 10; i++) {
movers[i] = new Mover(random(0.1, 2), random(width), random(height));
}

draw = function() {
background(255, 255, 255);

attractor.display();
for (var i = 0; i < movers.length; i++) {
var force = attractor.calculateAttraction(movers[i]);
movers[i].applyForce(force);

movers[i].update();
movers[i].display();
}
};