disable pump when container too small, see #256

js/common/model/MultipleParticleModel.js

@@ -227,14 +227,12 @@ class MultipleParticleModel extends PhetioObject {
         this.numMoleculesQueuedForInjectionProperty,
         this.isExplodedProperty,
         this.maxNumberOfMoleculesProperty,
-        this.containerHeightProperty,
         this.targetNumberOfMoleculesProperty
       ],
-      ( isPlaying, numberOfMoleculesQueuedForInjection, isExploded, maxNumberOfMoleculesProperty, containerHeight, targetNumberOfMolecules ) => {
+      ( isPlaying, numberOfMoleculesQueuedForInjection, isExploded, maxNumberOfMoleculesProperty, targetNumberOfMolecules ) => {
         return isPlaying &&
                numberOfMoleculesQueuedForInjection < MAX_MOLECULES_QUEUED_FOR_INJECTION &&
                !isExploded &&
-               ( containerHeight / this.particleDiameter ) > this.injectionPointY &&
                targetNumberOfMolecules < maxNumberOfMoleculesProperty;
       }
     );
@@ -265,13 +263,14 @@ class MultipleParticleModel extends PhetioObject {
     // @public, normalized velocity at which lid is moving in y direction
     this.normalizedLidVelocityY = 0;
 
+    // @protected (read-only) {Vector2} - the location where new molecules are injected, in normalized coordinates
+    this.injectionPoint = Vector2.ZERO.copy();
+
     // @private, various internal model variables
     this.particleDiameter = 1;
     this.minModelTemperature = null;
     this.residualTime = 0;
     this.moleculeInjectionHoldoffTimer = 0;
-    this.injectionPointX = 0;
-    this.injectionPointY = 0;
     this.heightChangeThisStep = 0;
     this.moleculeInjectedThisStep = false;
 
@@ -559,8 +558,10 @@ class MultipleParticleModel extends PhetioObject {
     this.updateNormalizedContainerDimensions();
 
     // Adjust the injection point based on the new particle diameter.  These are using the normalized coordinate values.
-    this.injectionPointX = CONTAINER_WIDTH / this.particleDiameter * INJECTION_POINT_HORIZ_PROPORTION;
-    this.injectionPointY = CONTAINER_INITIAL_HEIGHT / this.particleDiameter * INJECTION_POINT_VERT_PROPORTION;
+    this.injectionPoint.setXY(
+      CONTAINER_WIDTH / this.particleDiameter * INJECTION_POINT_HORIZ_PROPORTION,
+      CONTAINER_INITIAL_HEIGHT / this.particleDiameter * INJECTION_POINT_VERT_PROPORTION
+    );
 
     // Add the atoms and set their initial positions.
     this.initializeAtoms( phase );
@@ -703,7 +704,7 @@ class MultipleParticleModel extends PhetioObject {
 
     // Set the position(s) of the atom(s).
     const atomsPerMolecule = this.moleculeDataSet.atomsPerMolecule;
-    const moleculeCenterOfMassPosition = new Vector2( this.injectionPointX, this.injectionPointY );
+    const moleculeCenterOfMassPosition = this.injectionPoint.copy();
     const moleculeVelocity = new Vector2( xVel, yVel );
     const atomPositions = [];
     for ( let i = 0; i < atomsPerMolecule; i++ ) {

js/phase-changes/PhaseChangesModel.js

@@ -5,6 +5,7 @@
  */
 
 import BooleanProperty from '../../../axon/js/BooleanProperty.js';
+import DerivedProperty from '../../../axon/js/DerivedProperty.js';
 import NumberProperty from '../../../axon/js/NumberProperty.js';
 import Range from '../../../dot/js/Range.js';
 import Utils from '../../../dot/js/Utils.js';
@@ -56,6 +57,14 @@ class PhaseChangesModel extends MultipleParticleModel {
       range: new Range( MIN_ALLOWABLE_CONTAINER_HEIGHT, MultipleParticleModel.PARTICLE_CONTAINER_INITIAL_HEIGHT )
     } );
 
+    // @public (read-only) - a derived property that indicates whether the lid is higher than the injection point
+    this.lidAboveInjectionPointProperty = new DerivedProperty( [ this.containerHeightProperty ], containerHeight => {
+
+      // This may appear a little suspect, but the model is designed such that the container height is always reset
+      // to its max when the particle diameter and injection change, so this can be trusted.
+      return ( containerHeight / this.particleDiameter ) > this.injectionPoint.y;
+    } );
+
     // reset the target container height in the event of an explosion
     this.isExplodedProperty.lazyLink( isExploded => {
       if ( isExploded ) {

js/phase-changes/view/PhaseChangesScreenView.js

@@ -171,12 +171,14 @@ function PhaseChangesScreenView( model, isPotentialGraphEnabled, tandem ) {
     [
       model.isPlayingProperty,
       model.isExplodedProperty,
+      model.lidAboveInjectionPointProperty,
       model.maxNumberOfMoleculesProperty,
       model.targetNumberOfMoleculesProperty
     ],
-    ( isPlaying, isExploded, maxNumberOfMoleculesProperty, targetNumberOfMolecules ) => {
+    ( isPlaying, isExploded, lidAboveInjectionPoint, maxNumberOfMoleculesProperty, targetNumberOfMolecules ) => {
       return isPlaying &&
              !isExploded &&
+             lidAboveInjectionPoint &&
              targetNumberOfMolecules < maxNumberOfMoleculesProperty;
     }
   );