diff --git a/chp04_systems/NOC_4_03_ParticleSystemClass/NOC_4_03_ParticleSystemClass.pde b/chp04_systems/NOC_4_03_ParticleSystemClass/NOC_4_03_ParticleSystemClass.pde
index 935a214d..f9803d76 100644
--- a/chp04_systems/NOC_4_03_ParticleSystemClass/NOC_4_03_ParticleSystemClass.pde
+++ b/chp04_systems/NOC_4_03_ParticleSystemClass/NOC_4_03_ParticleSystemClass.pde
@@ -3,14 +3,17 @@
 // http://natureofcode.com
 
 ParticleSystem ps;
+PVector current;
 
 void setup() {
   size(640,360);
-  ps = new ParticleSystem(new PVector(width/2,50));
+  PVector origin= new PVector(width/2,50);
+  ps = new ParticleSystem(origin);
 }
 
 void draw() {
   background(255);
-  ps.addParticle();
+  current = new PVector(mouseX,mouseY);
+  ps.addParticle(current);
   ps.run();
-}
+}
\ No newline at end of file
diff --git a/chp04_systems/NOC_4_03_ParticleSystemClass/Particle.pde b/chp04_systems/NOC_4_03_ParticleSystemClass/Particle.pde
index 6bf46b10..b5816173 100644
--- a/chp04_systems/NOC_4_03_ParticleSystemClass/Particle.pde
+++ b/chp04_systems/NOC_4_03_ParticleSystemClass/Particle.pde
@@ -45,6 +45,4 @@ class Particle {
       return false;
     }
   }
-}
-
-
+}
\ No newline at end of file
diff --git a/chp04_systems/NOC_4_03_ParticleSystemClass/ParticleSystem.pde b/chp04_systems/NOC_4_03_ParticleSystemClass/ParticleSystem.pde
index 9f2c4b83..20c11377 100644
--- a/chp04_systems/NOC_4_03_ParticleSystemClass/ParticleSystem.pde
+++ b/chp04_systems/NOC_4_03_ParticleSystemClass/ParticleSystem.pde
@@ -13,8 +13,8 @@ class ParticleSystem {
     particles = new ArrayList<Particle>();
   }
 
-  void addParticle() {
-    particles.add(new Particle(origin));
+  void addParticle(PVector position) {
+    particles.add(new Particle(position.get()));
   }
 
   void run() {
@@ -26,8 +26,4 @@ class ParticleSystem {
       }
     }
   }
-}
-
-
-
-
+}
\ No newline at end of file
diff --git a/chp05_physicslibraries/CollisionsEqualMass/Mover.pde b/chp05_physicslibraries/CollisionsEqualMass/Mover.pde
index 04d8807d..8168ebc3 100644
--- a/chp05_physicslibraries/CollisionsEqualMass/Mover.pde
+++ b/chp05_physicslibraries/CollisionsEqualMass/Mover.pde
@@ -14,7 +14,7 @@ class Mover {
 
   Mover(PVector v, PVector l) {
     vel = v.get();
-    loc = l.get();
+    pos = l.get();
   }
 
   // Main method to operate object
@@ -56,19 +56,19 @@ class Mover {
     fill(175,200);
     ellipse(pos.x,pos.y,r*2,r*2);
     if (showVectors) {
-      drawVector(vel,loc,10);
+      drawVector(vel,pos,10);
     }
   }
 
   void collideEqualMass(Mover other) {
-    float d = PVector.dist(loc,other.loc);
+    float d = PVector.dist(pos,other.pos);
     float sumR = r + other.r;
     // Are they colliding?
     if (!colliding && d < sumR) {
       // Yes, make new velocities!
       colliding = true;
       // Direction of one object another
-      PVector n = PVector.sub(other.loc,loc);
+      PVector n = PVector.sub(other.pos,pos);
       n.normalize();
 
       // Difference of velocities so that we think of one object as stationary
@@ -95,6 +95,4 @@ PVector componentVector (PVector vector, PVector directionVector) {
   directionVector.normalize();
   directionVector.mult(vector.dot(directionVector));
   return directionVector;
-}
-
-
+}
\ No newline at end of file