​

function setup() {

  createCanvas(400, 400);

  ppm = 100;   // Number of pixels per meter

  th = 0.1;    // Pendulum angle theta

  v_th = 0;    // Angular velocity

  C = 2;       // Center point

  // Prague set-up according to Charles university lab http://kdt-40.karlov.mff.cuni.cz/

  L = 1.637;     // Length of the pendulum

  g = 9.810;

  dt = 1/50;

  t = 0;       // Current time

  num_swings = -0.25;  //Number of swings

  period = 0;

}

​

function draw() {

  background(220);

  old_th = th;     //Remember theta before calculation

  t = t + dt;

  a_th = -g/L*th;

  v_th = v_th + a_th*dt;

  th = th + v_th*dt;

  xp = C - L*sin(th);   // X coordinate of pendulum ball

  yp = L * cos(th);     // Y coordinate of pendulum ball

  scale(ppm);

  strokeWeight(1/ppm);

  line(C,0,xp,yp);

  ellipse(xp,yp,0.2,0.2);

  scale(1/ppm);

  textSize(20);

  text("t = "+nf(t,0,2), 50,50);

  if (th*old_th < 0) { 

    num_swings = num_swings + 0.5;

    period = t/num_swings;

  }

  text("N = "+nf(num_swings,0,2), 50, 75);

  text("Period = "+nf(period,0,3), 50, 100);

}