some changes
	new file:   eZLib/nbproject/configs/Study.Force.properties
	modified:   eZLib/src/eZLib/Physics/Force.java
	new file:   eZLib/src/eZLib/Physics/Friction.java
	new file:   eZLib/src/eZLib/Physics/Gravity.java
	modified:   eZLib/src/eZLib/Physics/Motion.java
	modified:   eZLib/src/eZLib/Sketch.java
	new file:   eZLib/src/eZLib/Study/ForceSketch.java
	modified:   eZLib/src/eZLib/Vector.java