Viscosity query parameters, see phetsims/density#67

js/common/DensityBuoyancyCommonQueryParameters.js

@@ -130,6 +130,25 @@ const DensityBuoyancyCommonQueryParameters = QueryStringMachine.getAll( {
   p2DynamicRelaxation: {
     type: 'number',
     defaultValue: 4
+  },
+
+  // Controls the proportional amount of overall result viscosity forces applied
+  viscosityMultiplier: {
+    type: 'number',
+    defaultValue: 1
+  },
+
+  // A mix between 0: Full viscosity is applied when any part of a mass is in the liquid, 1: The viscosity effect is
+  // multiplied times the proportion of the mass submerged (lowering viscosity when partially submerged).
+  viscositySubmergedRatio: {
+    type: 'number',
+    defaultValue: 0
+  },
+
+  // Viscosity for masses larger than this will be reduced to the force for this viscosity (somewhat of a hacK)
+  viscosityMassCutoff: {
+    type: 'number',
+    defaultValue: 2
   }
 } );
 

js/common/model/DensityBuoyancyModel.js

@@ -213,8 +213,12 @@ class DensityBuoyancyModel {
           }
 
           // Increase the generally-visible viscosity effect
+          const ratioSubmerged =
+            ( 1 - DensityBuoyancyCommonQueryParameters.viscositySubmergedRatio ) +
+            DensityBuoyancyCommonQueryParameters.viscositySubmergedRatio * submergedVolume / mass.volumeProperty.value;
           const hackedViscosity = this.liquidViscosityProperty.value ? 0.03 * Math.pow( this.liquidViscosityProperty.value / 0.03, 0.8 ) : 0;
-          const viscousForce = velocity.times( -hackedViscosity * Math.max( 2, mass.massProperty.value ) * 3000 );
+          const viscosityMass = Math.max( DensityBuoyancyCommonQueryParameters.viscosityMassCutoff, mass.massProperty.value );
+          const viscousForce = velocity.times( -hackedViscosity * viscosityMass * ratioSubmerged * 3000 * DensityBuoyancyCommonQueryParameters.viscosityMultiplier );
           this.engine.bodyApplyForce( mass.body, viscousForce );
         }
         else {