diff --git a/tutorials/multiphase/interDyMFoam/ras/floatingObject/0.org/pointDisplacement b/tutorials/multiphase/interDyMFoam/ras/floatingObject/0.org/pointDisplacement
index 711e09e22d868ecb68ee12141b909f673409fab7..b38ea4a3f75e869f5969872cccfcc40664c0ff69 100644
--- a/tutorials/multiphase/interDyMFoam/ras/floatingObject/0.org/pointDisplacement
+++ b/tutorials/multiphase/interDyMFoam/ras/floatingObject/0.org/pointDisplacement
@@ -37,7 +37,8 @@ boundaryField
         centreOfMass    (0.5 0.5 0.5);
         momentOfInertia (0.08622222 0.8622222 0.144);
         mass            9.6;
-        rhoInf          1;
+        rhoInf          1;                      // for forces calculation
+        // See sixDoFRigidBodyMotionState
         Q               (1 0 0 0 1 0 0 0 1);
         v               (0 0 0);
         a               (0 0 0);