public void update(int ms) {
float x = particle.getX();
float y = particle.getY();
Vector f = new Vector(0f, -0.001f, 0f);
float l = 50, r = 750;
float t = 550, b = 50;
if (x < l) f.x += 0.002f;
else if (x > r) f.x -= 0.002f;
if (y < b) f.y += 0.002f;
else if (y > t) f.y -= 0.002f;
particle.applyForce(f);
particle.integrate(ms);
particle.clearForces();
}
