class Particle {
  Vector3D loc;
  Vector3D vel;
  Vector3D acc;
  float theta;
  float theta_vel;
  float theta_acc;
  float particleSize;
  float x,y;

  Particle(Vector3D loc_, Vector3D vel_, float theta) {
    loc = loc_.copy();
    vel = vel_.copy();
    acc = new Vector3D(0,0);

    float x = loc.x * sin(theta);
    float y = loc.y * cos(theta);
    // is this good habit to call a class from another class?
    loc = new Vector3D(magnet.getLoc().x + x, magnet.getLoc().y + y);
    theta = 0.0f;
    theta_vel = 0.0f;
    particleSize = 1.0f;


  }

  public Vector3D getLoc() {
    return loc;
  }

  void calcForce(float amplitude_) {
    /*float G = 0.4; // universal gravity
    float dist = Vector3D.distance(loc,magnet.getLoc());
    //println(dist);
    theta_acc = ( G / amplitude_ ) * sin(theta);
    theta_vel += theta_acc + 0.005;
    theta += theta_vel;
    // println(theta);
    // loc.add(vel);


    x = dist  * sin(theta);
    y = dist  * cos(theta);
    loc.x = magnet.getLoc().x + x;
    loc.y = magnet.getLoc().y + y;*/
   
  }
  
  void changeColor() {
    float dist = Vector3D.distance(magnet.loc,loc);
   
    fill(dist,255-dist,255);
    }
    
  
  void run() {
     vel.add(acc);
     loc.add(vel);
     acc.setXYZ(0,0,0);
  }
  
  void add_force(Vector3D v) {
     acc.add(v);
  }
  
  void render() {
    //stroke(255,50);
    ellipseMode(CENTER);
    //stroke(255);
    //  println(disp.x);
    noStroke();
    ellipse(loc.x, loc.y,3,3);
    fill(0,0,0,20);
    ellipse(loc.x, loc.y,10,10);

  }
}