pendulum

float dt = 0.2;

float angle = 0.001;

float g = 9.8;

float x;

float y;

float l =140; //length of the rope

float at;     //tangent acceleration

float rotacc; //rotary acceleration

float rotvel = 0.04; //rotary velocity

​

boolean spotted = false;

boolean grabbed = false;

​

void setup(){

  size(300, 300);

}

​

​

void draw(){

  background(255);

  if(!grabbed){

  at = g * sin(angle);

​

  rotacc = at / l;

  rotacc -= rotvel * 0.01;

  rotvel += rotacc * dt;

  angle += rotvel *dt;

  }else{

    angle = PVector.angleBetween(new PVector(0, -1), new PVector(-width/2 + mouseX, -height/2 + mouseY));

    if(-width/2 + mouseX<0)

    angle *=-1;

    rotvel = 0;

  }

  y = -l * cos(angle);

  x = l * sin(angle);;

  translate(width / 2 , height / 2);

  line(0,0,x,y);

  if((spotted = PVector.dist(new PVector(-width/2 + mouseX, -height/2 + mouseY), new PVector(x, y)) < 10) || grabbed)

      fill(0,0,255);

      else fill(255);

  ellipse(x, y, 20 , 20);

}

​

void mousePressed(){

  grabbed = spotted;

}

​

void mouseReleased(){

  grabbed = false;

}