 
         return element.direction.scale(-m)
 
+
+    # Return the force of gravity on the given element.
+    #
+    # @param element {Object} 
+    gravity : (element) ->
+        force = new timber.Vector(0, @gravitationalConstant)
+        
 
 # 
 # An abstract base class for any drawable thing.

        for element in elements

            # Find the net force on the element.
            forces = [element.velocity(), @drag(element)]

            resultant = forces.reduce (t, s) -> t.sum(s)    #FIXME: not portable


        @logger.debug("Initializing")

        @density = 10  # The density of the environment's medium. 
        @gravitationalConstant = 0.5


    # Update the elements with the effects of the given number of milliseconds
