(mkosarek) Updated discussion on what we mean when we say rigid body

2 files changed, 48 insertions, 24 deletions

diff --git a/2d/rigidbody/rigidbody_1.html b/2d/rigidbody/rigidbody_1.html
index 9ef056c..8e78972 100644
--- a/2d/rigidbody/rigidbody_1.html
+++ b/2d/rigidbody/rigidbody_1.html
@@ -74,20 +74,32 @@
 	</p>
   </section>
   <section>
-    <h2>What do we mean by 'Rigid Body Physics'?</h2>
-    In implementing a rigidy body physics system, we're primarily interested in two sub-fields of physics, namely <b>dynamics</b> and <b>kinematics</b>. Although I'm
-    far as can be from being an expert in either of these fields, I will explain - from a programmer's perspective - what they mean to me:
+    <h2>What do we mean by Rigid Body Physics?</h2>
+    <p>
+      When we say that the objects in our scene have "rigidbodies", we are assuming the following things:
+      <ul>
+        <li>The object can never be disformed by the physics system. This means that, when collisions happen, objects will always bounce off of one another. There will never be an instance where one object squishes or puts a hole into another object. No penetration is allowed.</li>
+        <li>Mass is uniformly distributed throughout the object. This assumption allows us to think of the rigidbody as a single point, which represents the center of mass of our object. You will notice later in this tutorial that the rigidbody formulas work regardless of the shape and size of the object as a result of this assumption.</li>
+      </ul>
+      With that knowledge in mind, let's start digging into some implementation.
+    </p>
+  </section>
+  <section>
+    <h2>A Tale of Two Sub-Fields</h2>
+    <p>
+      When discussing a rigidy body physics system, we're interested in two sub-fields of physics, namely <b>dynamics</b> and <b>kinematics</b>. Although I'm far as can be from being an expert in either of these fields, I will explain - from a programmer's perspective - what they mean to me:
 
-    <ul>
-      <li>
-        <b>Kinematics</b> is the study of how an object's movement changes over time. These are the classic position, velocity, and acceleration equations that you're most likely familiar with from high school or college physics. Kinematics doesn't care about <i>how</i> a system entered into the state that it is in, but rather that the system <i>is</i> in that state.
-      </li>
-      <li>
-        <b>Dynamics</b> is the study of whats <i>causes</i> kinematic movement. These are the classic force and momentum equations that you may already be familiar with as well. Whereas kinematics only worries itself with the current state of the system, dynamics wants to know <i>how</i> the system entered the state that it is currently in.
-      </li>
-    </ul>
+      <ul>
+        <li>
+          <b>Kinematics</b> is the study of how an object's movement changes over time. These are the classic position, velocity, and acceleration equations that you're most likely familiar with from high school or college physics. Kinematics doesn't care about <i>how</i> a system entered into the state that it is in, but rather that the system <i>is</i> in that state.
+        </li>
+        <li>
+          <b>Dynamics</b> is the study of whats <i>causes</i> kinematic movement. These are the classic force and momentum equations that you may already be familiar with as well. Whereas kinematics only worries itself with the current state of the system, dynamics wants to know <i>how</i> the system entered the state that it is currently in.
+        </li>
+      </ul>
 
-    Although the distinction between these two subfields may seem inconsequential, it impacts the conceptual way in which we might begin to setup our 2D rigidbody simulation: <i>the kinematic variables are the data that we act upon, while the dynamics variables are the data that we apply</i>. 
+      Although the distinction between these two subfields may seem inconsequential, it impacts the conceptual way in which we might begin to setup our 2D rigidbody simulation: <i>the kinematic variables are the data that we act upon, while the dynamics variables are the data that we apply</i>. 
+    </p>
 
   </section>
   <section>
diff --git a/2d/rigidbody/rigidbody_1.html.content b/2d/rigidbody/rigidbody_1.html.content
index 6e7d46b..c54fdab 100644
--- a/2d/rigidbody/rigidbody_1.html.content
+++ b/2d/rigidbody/rigidbody_1.html.content
@@ -22,20 +22,32 @@
 	</p>
   </section>
   <section>
-    <h2>What do we mean by 'Rigid Body Physics'?</h2>
-    In implementing a rigidy body physics system, we're primarily interested in two sub-fields of physics, namely <b>dynamics</b> and <b>kinematics</b>. Although I'm
-    far as can be from being an expert in either of these fields, I will explain - from a programmer's perspective - what they mean to me:
+    <h2>What do we mean by Rigid Body Physics?</h2>
+    <p>
+      When we say that the objects in our scene have "rigidbodies", we are assuming the following things:
+      <ul>
+        <li>The object can never be disformed by the physics system. This means that, when collisions happen, objects will always bounce off of one another. There will never be an instance where one object squishes or puts a hole into another object. No penetration is allowed.</li>
+        <li>Mass is uniformly distributed throughout the object. This assumption allows us to think of the rigidbody as a single point, which represents the center of mass of our object. You will notice later in this tutorial that the rigidbody formulas work regardless of the shape and size of the object as a result of this assumption.</li>
+      </ul>
+      With that knowledge in mind, let's start digging into some implementation.
+    </p>
+  </section>
+  <section>
+    <h2>A Tale of Two Sub-Fields</h2>
+    <p>
+      When discussing a rigidy body physics system, we're interested in two sub-fields of physics, namely <b>dynamics</b> and <b>kinematics</b>. Although I'm far as can be from being an expert in either of these fields, I will explain - from a programmer's perspective - what they mean to me:
 
-    <ul>
-      <li>
-        <b>Kinematics</b> is the study of how an object's movement changes over time. These are the classic position, velocity, and acceleration equations that you're most likely familiar with from high school or college physics. Kinematics doesn't care about <i>how</i> a system entered into the state that it is in, but rather that the system <i>is</i> in that state.
-      </li>
-      <li>
-        <b>Dynamics</b> is the study of whats <i>causes</i> kinematic movement. These are the classic force and momentum equations that you may already be familiar with as well. Whereas kinematics only worries itself with the current state of the system, dynamics wants to know <i>how</i> the system entered the state that it is currently in.
-      </li>
-    </ul>
+      <ul>
+        <li>
+          <b>Kinematics</b> is the study of how an object's movement changes over time. These are the classic position, velocity, and acceleration equations that you're most likely familiar with from high school or college physics. Kinematics doesn't care about <i>how</i> a system entered into the state that it is in, but rather that the system <i>is</i> in that state.
+        </li>
+        <li>
+          <b>Dynamics</b> is the study of whats <i>causes</i> kinematic movement. These are the classic force and momentum equations that you may already be familiar with as well. Whereas kinematics only worries itself with the current state of the system, dynamics wants to know <i>how</i> the system entered the state that it is currently in.
+        </li>
+      </ul>
 
-    Although the distinction between these two subfields may seem inconsequential, it impacts the conceptual way in which we might begin to setup our 2D rigidbody simulation: <i>the kinematic variables are the data that we act upon, while the dynamics variables are the data that we apply</i>. 
+      Although the distinction between these two subfields may seem inconsequential, it impacts the conceptual way in which we might begin to setup our 2D rigidbody simulation: <i>the kinematic variables are the data that we act upon, while the dynamics variables are the data that we apply</i>. 
+    </p>
 
   </section>
   <section>