// The Coding Train / Daniel Shiffman

// https://thecodingtrain.com/CodingChallenges/159-simple-pendulum-simulation.html

// https://youtu.be/NBWMtlbbOag

​

class Pendulum {

​

  constructor(x, y, r) {

    this.origin = createVector(x, y);

    this.position = createVector();

    this.r = r;

    this.angle = PI / 4;

​

    this.aVelocity = 0.0;

    this.aAcceleration = 0.0;

    this.damping = 1;//0.995; 

    this.ballr = 48.0; 

  }

​

  update() {

    let gravity = 0.4;

    this.aAcceleration = (-1 * gravity / this.r) * sin(this.angle); // Calculate acceleration (see: http://www.myphysicslab.com/pendulum1.html)

    this.aVelocity += this.aAcceleration; // Increment velocity

    //this.aVelocity *= this.damping; // Arbitrary damping

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

  }

​

  show() {

    this.position.set(this.r * sin(this.angle), this.r * cos(this.angle), 0); // Polar to cartesian conversion

    this.position.add(this.origin); // Make sure the position is relative to the pendulum's origin

​

    stroke(255);

    strokeWeight(2);

    // Draw the arm

    line(this.origin.x, this.origin.y, this.position.x, this.position.y);

    ellipseMode(CENTER);

    fill(127);

    // Draw the ball

    ellipse(this.position.x, this.position.y, this.ballr, this.ballr);

  }

}