Pendulum.java

final float g = 0.5, m1 = 1, l1 = 100;
final float i = m1 * l1 * l1 / 3; // m*L^2/3
float a = 0, v = 0.01, x = -PI / 2 + 0.1;

void setup()
{
  size(500, 500);
}

void draw()
{
  // Draw
  
  background(255);
  
  line(width / 2, height / 2, width / 2 + l1 * cos(x), height / 2 + l1 * sin(x));
  
  ellipse(width / 2, height / 2, 5, 5);
  
  // Calculate
  
  a = l1 / 2 * g * sin(x + PI / 2) / i;
  v += a;
  x += v;
  
  println("a=" + a + " v=" + v + " x=" + x);
}