Notion - Update docs

notion-docs/03_forces.md

@@ -0,0 +1,99 @@
+<section data-type="sect1" id="chapter02_section4">
+<h2>2.4 Dealing with Mass</h2>
+<a data-primary="mass" data-secondary="modeling" data-type="indexterm"></a>
+<a data-primary="natural phenomena" data-secondary="mass" data-tertiary="modeling"
+data-type="indexterm"></a>
+<p>
+OK. I’ve got one small (but fundamental) addition to make before
+integrating forces into the <code>Mover</code> class. After all, Newton’s second law is really
+<span data-type="equation">\vec{F} = M \times \vec{A}</span>, not
+<span data-type="equation">\vec{F} = \vec{A}</span>. Incorporating mass is
+as easy as adding an instance variable to the class, but I need to spend
+a little more time here because of another impending complication.
+</p>
+<p>First I’ll add mass.</p>
+<pre data-code-language="javascript" data-type="programlisting" class="codesplit">
+class Mover {
+constructor(){
+this.position = createVector();
+this.velocity = createVector();
+this.acceleration = createVector();
+//{!1} Adding mass as a number
+this.mass = ????;
+}
+}</pre>
+<a data-primary="mass" data-secondary="units of measurement" data-tertiary="defining"
+data-type="indexterm"></a>
+<div data-type="note">
+<h2>Units of Measurement</h2>
+<p>
+Now that I am introducing mass, it’s important to make a quick note
+about units of measurement. In the real world, things are measured in
+specific units. Two objects are 3 meters apart, the baseball
+is moving at a rate of 90 miles per hour, or this bowling ball has a
+mass of 6 kilograms. As you’ll see later in this book, sometimes you will
+want to take real-world units into consideration. However, in this
+chapter, I’m going to ignore them for the most part. The units of
+measurement are in pixels (“These two circles are 100 pixels apart”) and
+frames of animation (“This circle is moving at a rate of 2 pixels per
+frame”). In the case of mass, there isn’t any unit of measurement
+to use. I’m just going to make something up. In this example, I will
+arbitrarily picking the number 10. There is no unit of measurement,
+though you might enjoy inventing a unit of your own, like “1 moog” or “1
+yurkle.” It should also be noted that, for demonstration purposes, I’ll
+tie mass to pixels (drawing, say, a circle with a radius of 10). This
+will allow me to visualize the mass of an object albeit inaccurately. In the real
+world size does not indicate mass. A small metal ball could have a much higher mass than a
+large balloon due to its higher density. And for two circular objects with equal density,
+the mass should be tied to the formula for area which is not as simple as the radius alone.
+</p>
+</div>
+<p>
+Mass is a scalar, not a vector, as it’s just one number describing
+the amount of matter in an object. I could get fancy and
+compute the area of a shape as its mass, but it’s simpler to begin by
+saying, “Hey, the mass of this object is…um, I dunno…how about 10?”
+</p>
+<pre data-code-language="javascript" data-type="programlisting" class="codesplit">
+constructor() {
+this.position = createVector(random(width), random(height));
+this.velocity = createVector(0, 0);
+this.acceleration = createVector(0, 0);
+this.mass = 10;
+}</pre>
+<a data-primary="forces" data-secondary="applying to objects" data-type="indexterm"></a>
+<p>
+This isn’t so great since things only become interesting once I have
+objects with varying mass, but it’s enough to get us started. Where does mass come
+in? It’s needed for applying Newton’s second law to the object.
+</p>
+<pre data-code-language="javascript" data-type="programlisting" class="codesplit">
+applyForce(force) {
+//{!2} Newton's second law (with force accumulation and mass)
+force.div(mass);
+this.acceleration.add(force);
+}</pre>
+<p>
+Yet again, even though the code looks quite reasonable, there is a
+major problem here. Consider the following scenario with two
+<code>Mover</code> objects, both being blown away by a wind force.
+</p>
+<pre data-code-language="java" data-type="programlisting" class="codesplit">
+let m1 = new Mover();
+let m2 = new Mover();
+let wind = createVector(1, 0);
+m1.applyForce(wind);
+m2.applyForce(wind);</pre>
+<p>
+Again, I’ll <em>be</em> the computer. Object <code>m1</code> receives the
+wind force—(1,0)—divides it by mass (10), and adds it to acceleration.
+</p>
+<p>
+<span class="formula">m1 equals wind force: &nbsp;&nbsp;&nbsp;
+(1,0)</span><br />
+<span class="formula">Divided by mass of 10: &nbsp;&nbsp; (0.1,0)</span>
+</p>
+<a data-primary="object-oriented programming"
+data-secondary="references to vs. copies of objects" data-type="indexterm"></a>
+<p>
+OK. Moving on to object <code>m2</code>. It also receives the wind