diff --git a/source/Entity.cpp b/source/Entity.cpp
index 5f14a5e5..c614c8e9 100644
--- a/source/Entity.cpp
+++ b/source/Entity.cpp
@@ -33,6 +33,7 @@ cEntity::cEntity(eEntityType a_EntityType, double a_X, double a_Y, double a_Z)
 	, m_HeadYaw( 0.0 )
 	, m_Rot(0.0, 0.0, 0.0)
 	, m_Pos(a_X, a_Y, a_Z)
+	, m_Mass (0.001) //Default 1g
 	, m_bDirtyHead(true)
 	, m_bDirtyOrientation(true)
 	, m_bDirtyPosition(true)
@@ -506,6 +507,25 @@ void cEntity::SetHeadYaw(double a_HeadYaw)
 
 
 
+void cEntity::SetMass(double a_Mass)
+{
+	if (a_Mass > 0)
+	{
+		m_Mass = a_Mass;
+	}
+	else
+	{
+		//Make sure that mass is not zero. 1g is the default because we 
+		//have to choose a number. It's perfectly legal to have a mass 
+		//less than 1g as long as is NOT equal or less than zero.
+		m_Mass = 0.001;
+	}
+}
+
+
+
+
+
 void cEntity::SetRotation(double a_Rotation)
 {
 	m_Rot.x = a_Rotation;
diff --git a/source/Entity.h b/source/Entity.h
index 3009bc61..779ce535 100644
--- a/source/Entity.h
+++ b/source/Entity.h
@@ -107,6 +107,7 @@ public:
 	cWorld * GetWorld(void) const { return m_World; }
 
 	double           GetHeadYaw   (void) const {return m_HeadYaw; }
+	double           GetMass      (void) const {return m_Mass; }
 	const Vector3d & GetPosition  (void) const {return m_Pos; }
 	double           GetPosX      (void) const {return m_Pos.x; }
 	double           GetPosY      (void) const {return m_Pos.y; }
@@ -125,6 +126,7 @@ public:
 	int GetChunkZ(void) const {return FAST_FLOOR_DIV(((int)m_Pos.z), cChunkDef::Width); }
 
 	void SetHeadYaw (double a_HeadYaw);
+	void SetMass    (double a_Mass);
 	void SetPosX    (double a_PosX);
 	void SetPosY    (double a_PosY);
 	void SetPosZ    (double a_PosZ);
@@ -247,11 +249,18 @@ protected:
 	void ReferencedBy( cEntity*& a_EntityPtr );
 	void Dereference( cEntity*& a_EntityPtr );
 private:
+	//Measured in degrees (MAX 360°)
 	double   m_HeadYaw;
+	//Measured in meter/second (m/s)
 	Vector3d m_Speed;
+	//Measured in degrees (MAX 360°)
 	Vector3d m_Rot;
+	//Measured in meters (1 meter = 1 block) (m)
 	Vector3d m_Pos;
+	//Measured in meter/second
 	Vector3d m_WaterSpeed;
+	//Measured in Kilograms (Kg)
+	double m_Mass
 } ;  // tolua_export
 
 typedef std::list<cEntity *> cEntityList;