--- a/CHANGES.html	Sun Nov 06 17:46:16 2011 +0100
+++ b/CHANGES.html	Thu Nov 17 19:02:45 2011 +0100
@@ -76,6 +76,7 @@
 
 <h2>New API:</h2>
 <ul>
+<li> In the mobility module, there is a new API MobilityModel::GetRelativeSpeed() returning the relative speed of two objects. Proposed by Jens Mittag.</li>
 </ul>
 
 <h2>Changes to existing API:</h2>

--- a/src/mobility/model/mobility-model.cc	Sun Nov 06 17:46:16 2011 +0100
+++ b/src/mobility/model/mobility-model.cc	Thu Nov 17 19:02:45 2011 +0100
@@ -83,6 +83,15 @@
   return CalculateDistance (position, oPosition);
 }
 
+double
+MobilityModel::GetRelativeSpeed (Ptr<const MobilityModel> other) const
+{
+  double x = GetVelocity().x - other->GetVelocity().x;
+  double y = GetVelocity().y - other->GetVelocity().y;
+  double z = GetVelocity().z - other->GetVelocity().z;
+  return sqrt( (x*x) + (y*y) + (z*z) );
+}
+
 void
 MobilityModel::NotifyCourseChange (void) const
 {

--- a/src/mobility/model/mobility-model.h	Sun Nov 06 17:46:16 2011 +0100
+++ b/src/mobility/model/mobility-model.h	Thu Nov 17 19:02:45 2011 +0100
@@ -60,6 +60,12 @@
    * \return the distance between the two objects. Unit is meters.
    */
   double GetDistanceFrom (Ptr<const MobilityModel> position) const;
+  /**
+   * \param other reference to another object's mobility model
+   * \return the relative speed between the two objects. Unit is meters/s.
+   */
+  double GetRelativeSpeed (Ptr<const MobilityModel> other) const;
+
 protected:
   /**
    * Must be invoked by subclasses when the course of the