constructor(x, length, angle) {

    this.originX = x;

    this.originY = 0;

    this.length = length;

    this.angle = angle;

    this.aVelocity = 0;

    this.aAcceleration = 0;

    this.x = 0;

    this.y = 0;

    this.updatePosition();

  }

  collide(other){

     if (dist(this.x, this .y, other.x, other.y) < ballDiameter) {

      let vA = this.aVelocity;

      let vB = other.aVelocity;

      // Exchange angular velocities with restitution factor

      this.aVelocity = vB * restitution;

      other.aVelocity = vA * restitution;

      this.angle=0;

      other.angle=0;

    }

  }

  update() {

    this.aAcceleration = (-1 * gravity / this.length) * sin(this.angle); // Calculate angular acceleration

    this.aVelocity += this.aAcceleration; // Update angular velocity

    this.aVelocity *= damping; // Apply damping

    this.angle += this.aVelocity; // Update angle

    this.updatePosition();

  }

  updatePosition() {

    // Calculate ball position

    this.x = this.originX + this.length * sin(this.angle);

    this.y = this.originY + this.length * cos(this.angle);

  }

  display() {

    // Draw the string

    stroke(0);

    line(this.originX, this.originY, this.x, this.y);

    // Draw the ball

    fill(127);

    ellipse(this.x, this.y, ballDiameter);

  }

}

​