// The Coding Train / Daniel Shiffman

// https://thecodingtrain.com/CodingChallenges/160-spring-forces.html

// https://youtu.be/Rr-5HiXquhw

​

// Simple Spring: https://editor.p5js.org/codingtrain/sketches/dcd6-2mWa

// Spring Vector: https://editor.p5js.org/codingtrain/sketches/_A2pm_SSg

// Spring OOP: https://editor.p5js.org/codingtrain/sketches/9BAoEn4Po

// Soft Spring: https://editor.p5js.org/codingtrain/sketches/S5dY7qjxP

​

let angle;

let angleV = 0;

let angleA = 0;

​

let bob;

let len;

let origin;

​

let gravity = 1;

​

let y = 250;

let velocity = 0;

let restLength = 200;

let k = 0.005;

let kSlider;

​

function setup() {

  createCanvas(600, 400);

  kSlider = createSlider(0, 0.01, k, 0);

  createSpan(`K (0-0.01)`);

  origin = createVector(300, 0);

  angle = PI / 4;

  bob = createVector(0, y);

  //location.href = "https://editor.p5js.org/codingtrain/sketches/SN-39sHAC";

}

​

function draw() {

  background(112, 50, 126);

  k = kSlider.value();

  stroke(255);

  strokeWeight(8);

  line(origin.x, origin.y, bob.x, bob.y);

  noStroke();

  fill(45, 197, 244);

  circle(bob.x, bob.y, 64);

​

  // Wrong! len = y = bob.y;

  len = dist(bob.x, bob.y, origin.x, origin.y);

  y = bob.y;

​

  /* Pendulum stuff */ {

    let force = gravity * sin(angle);

    angleA = (-1 * force) / len;

    angleV += angleA;

    angle += angleV;

​

    // angleV *= 0.99;

​

    bob.x = len * sin(angle) + origin.x;

    bob.y = len * cos(angle) + origin.y;

  }

​

  /* Spring stuff */ {

    let x = y - restLength;

    let springForce = -k * x;

​

    // F = A

    velocity += springForce;

    bob.y += velocity;

​

    velocity *= 0.99;

  }

}

​