diff --git a/js/friction/FrictionA11yStrings.js b/js/friction/FrictionA11yStrings.js
index 49a0ac87..86582cc8 100644
--- a/js/friction/FrictionA11yStrings.js
+++ b/js/friction/FrictionA11yStrings.js
@@ -10,6 +10,7 @@
 define( function( require ) {
   'use strict';
 
+  // modules
   var friction = require( 'FRICTION/friction' );
 
   var FrictionA11yStrings = {
diff --git a/js/friction/model/FrictionModel.js b/js/friction/model/FrictionModel.js
index 8e13c1d9..26b27407 100644
--- a/js/friction/model/FrictionModel.js
+++ b/js/friction/model/FrictionModel.js
@@ -21,6 +21,7 @@ define( function( require ) {
   var Vector2 = require( 'DOT/Vector2' );
   var Vector2IO = require( 'DOT/Vector2IO' );
 
+  // constants
   var ATOM_RADIUS = FrictionSharedConstants.ATOM_RADIUS; // radius of single atom
   var ATOM_SPACING_X = 20; // x-distance between neighbors (atoms)
   var ATOM_SPACING_Y = 20; // y-distance between neighbors (atoms)
diff --git a/js/friction/view/book/CoverNode.js b/js/friction/view/book/CoverNode.js
index 573468f8..07718405 100644
--- a/js/friction/view/book/CoverNode.js
+++ b/js/friction/view/book/CoverNode.js
@@ -8,6 +8,7 @@
 define( function( require ) {
   'use strict';
 
+  // modules
   var FrictionSharedConstants = require( 'FRICTION/friction/FrictionSharedConstants' );
   var inherit = require( 'PHET_CORE/inherit' );
   var Node = require( 'SCENERY/nodes/Node' );