multiple pendulums

Pendulum.pde

class Pendulum {
  PVector origin;
  PVector bob;
  float arm; // length of arm
  float r;
  float angle, aV, aA;
  Pendulum(float x, float y, float a) {
    origin = new PVector(x, y);
    bob = new PVector(origin.x, arm);
    arm = 150.0;
    r = 20;
    angle = a;
    aV = 0.0;
    aA = 0.0;
  }
  void swing() {
    aA = -0.00981*sin(angle);
    aV += aA;
    aV *= 0.999;
    angle += aV;
    bob.x = origin.x+arm*sin(angle);
    bob.y = origin.y+arm*cos(angle);
  }
  void display() {
    stroke(255);
    line(origin.x, origin.y, bob.x, bob.y);
    ellipse(bob.x, bob.y, r, r);
  }
}

pendulum1.pde

int w = 800;
int h = 300;
int cx, cy;
float theta;
int numPends;
float G = 0.981;
PVector gravity;
Pendulum[] pends;

void setup() {
  size(w, h);
  background(0);
  cx = width/2;
  cy = height/2;
  gravity = new PVector(0, G);
  theta = 0.0;
  setupPends();
}

void setupPends() {
  numPends = 5;
  pends = new Pendulum[numPends];
  for (int i = 0; i < numPends; i++) {
    Pendulum p = new Pendulum(cx, 0, theta-(i*(theta/numPends)));
    pends[i] = p;
  }
}

void draw() {
  background(0);
  text("click to start", cx, cy+50);
  for (int i = 0; i < pends.length; i++) {
    Pendulum p = pends[i];
    p.swing();
    p.display();
  }
}

void mouseReleased() {
  float dx = mouseX - cx;
  float dy = mouseY;
  theta = atan(dx/dy);
  setupPends();
}