Forces
Demonstration of multiple force acting on bodies (natureofcode.com)
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// Demonstration of multiple force acting on
// bodies (Mover class)
// Bodies experience gravity continuously
// Bodies experience fluid resistance when in "water"
// Five moving bodies
let movers = [];
// Liquid
let liquid;
function setup() {
createCanvas(640, 360);
reset();
// Create liquid object
liquid = new Liquid(0, height / 2, width, height / 2, 0.1);
}
function draw() {
background(127);
// Draw water
liquid.display();
for (let i = 0; i < movers.length; i++) {
// Is the Mover in the liquid?
if (liquid.contains(movers[i])) {
// Calculate drag force
let dragForce = liquid.calculateDrag(movers[i]);
// Apply drag force to Mover
movers[i].applyForce(dragForce);
}
// Gravity is scaled by mass here!
let gravity = createVector(0, 0.1 * movers[i].mass);
// Apply gravity
movers[i].applyForce(gravity);
// Update and display
movers[i].update();
movers[i].display();
movers[i].checkEdges();
}
}
function mousePressed() {
reset();
}
// Restart all the Mover objects randomly
function reset() {
for (let i = 0; i < 9; i++) {
movers[i] = new Mover(random(0.5, 3), 40 + i * 70, 0);
}
}
let Liquid = function(x, y, w, h, c) {
this.x = x;
this.y = y;
this.w = w;
this.h = h;
this.c = c;
};
// Is the Mover in the Liquid?
Liquid.prototype.contains = function(m) {
let l = m.position;
return l.x > this.x && l.x < this.x + this.w &&
l.y > this.y && l.y < this.y + this.h;
};
// Calculate drag force
Liquid.prototype.calculateDrag = function(m) {
// Magnitude is coefficient * speed squared
let speed = m.velocity.mag();
let dragMagnitude = this.c * speed * speed;
// Direction is inverse of velocity
let dragForce = m.velocity.copy();
dragForce.mult(-1);
// Scale according to magnitude
// dragForce.setMag(dragMagnitude);
dragForce.normalize();
dragForce.mult(dragMagnitude);
return dragForce;
};
Liquid.prototype.display = function() {
noStroke();
fill(50);
rect(this.x, this.y, this.w, this.h);
};
function Mover(m, x, y) {
this.mass = m;
this.position = createVector(x, y);
this.velocity = createVector(0, 0);
this.acceleration = createVector(0, 0);
}
// Newton's 2nd law: F = M * A
// or A = F / M
Mover.prototype.applyForce = function(force) {
let f = p5.Vector.div(force, this.mass);
this.acceleration.add(f);
};
Mover.prototype.update = function() {
// Velocity changes according to acceleration
this.velocity.add(this.acceleration);
// position changes by velocity
this.position.add(this.velocity);
// We must clear acceleration each frame
this.acceleration.mult(0);
};
Mover.prototype.display = function() {
stroke(0);
strokeWeight(2);
fill(255,127);
ellipse(this.position.x, this.position.y, this.mass * 16, this.mass * 16);
};
// Bounce off bottom of window
Mover.prototype.checkEdges = function() {
if (this.position.y > (height - this.mass * 8)) {
// A little dampening when hitting the bottom
this.velocity.y *= -0.9;
this.position.y = (height - this.mass * 8);
}
};
