javascript - 向量数学在其中一个函数中关闭

Question

我打算在 2D 平面上模拟重力加速度（简化，没有重力常数）。我的代码在控制台中被解释没有任何错误，但是两个圆圈没有慢慢地相互加速，而是相互远离。加速度似乎保持在 0。我无法理解这种行为。

// orbiters is gonna be the array containing the two celestial bodies 
var orbiters;
var sun;
var earth;
function setup() {
  frameRate(.3);
  console.log("starting the program")
  createCanvas(640, 480);
  sun = new Orbiter(10, 0, 0, width/2, height/2);
  earth = new Orbiter (1, 0, 0, width/5, height/4);
  orbiters = [sun, earth];
}

function draw() {
  console.log("starting the loop")
  background(15, 40, 20);
  // [missing: calculate gravity acceleration], then update position, display position. 
  orbiters.forEach(function(celBody) { 
    celBody.update();
    })
  orbiters.forEach(function(celBody) { 
    celBody.display();
    })
    // for each celestial body, accelerate it towards every other celestial body
  orbiters.forEach(function(celBody){
    orbiters.forEach(function (otherCelBody){
      if(celBody != otherCelBody){
        celBody.gravityAccelerate(otherCelBody.weight, otherCelBody.pos)
      }
    })
  })
}
// No volume for now: describe a body with weight, velocity, position
function Orbiter(weight, vx, vy, posx, posy) {
  this.weight = weight;
  this.pos = createVector(posx, posy);
  this.vel = createVector(vx, vy);
  this.acc = createVector(0, 0);
  
  //this finds an acceleration and an angle and gives out a vector to accelerate a body by
  this.gravityAccelerate = function(otherBodyWeight, otherBodyPosition) {
    
    // calculate magnitude
    gravDistance = sqrt(sq(otherBodyPosition.x - this.pos.x)+sq(otherBodyPosition.y - this.pos.y));
    // calculate angle
    gravHeading = createVector(otherBodyPosition.sub(this.pos)).heading();
    // calculate force and divide by own mass(acceleration amount)
    gravForce = (this.weight * otherBodyWeight) / gravDistance;
// calculate gravitational acceleration's magnitude as a vector
    gravAccMag = gravForce / this.weight;
    // apply amount to angle and give a vector
    console.log("gravity acceleration = ")
    gravAccVec = createVector(Math.cos(gravHeading), Math.sin(gravHeading));
// display gravitational acceleration vector
    console.log(gravAccVec.x);
    console.log(gravAccVec.y);
    console.log("this body's acceleration = ");
    console.log(this.acc.x);
    console.log(this.acc.y);
    this.acc = this.acc.add(gravAccVec);
    console.log("this body's position")
    console.log(this.pos.x)
    console.log(this.pos.x)
  }
  
  this.update = function() {
    this.vel.add(this.acc);
    this.pos.add(this.vel);
  }
  
  this.display = function() {
    this.size = sqrt(this.weight * 10);
    fill (60, 180, 70);
    ellipse(this.pos.x, this.pos.y, this.size, this.size);
  }
}

我尝试降低帧率以更好地分析执行，两个圆圈的初始位置似乎正确。它们似乎被排斥而不是被吸引，更奇怪的是，我看到了位置的变化，但总加速度 (this.acc) 和重力加速度变化 (gravAccVec) 的值为 0 并且不改变，并且航向的重力加速度矢量是null，所以我不明白是什么导致了排斥运动。改变权重值不会影响结果，甚至切换正弦和余弦来评估重力矢量的角度也不会改变任何东西：

body1(x,y)  body2(x,y)
320,240     -192,-120
512,360     -704,-480
1216,840    -1920,-1320
3136,2160   -5056,-3480

要执行此代码，您需要导入 p5.js 库。

标签： javascriptmathvectorp5.js