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diff --git a/src/main/scala/sims/dynamics/Shape.scala b/src/main/scala/sims/dynamics/Shape.scala
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+++ b/src/main/scala/sims/dynamics/Shape.scala
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+/*
+ * Simple Mechanics Simulator (SiMS)
+ * copyright (c) 2009 Jakob Odersky
+ * made available under the MIT License
+*/
+
+package sims.dynamics
+
+import sims.geometry._
+import sims.collision._
+
+/**
+* An abstract shape.
+*/
+abstract class Shape{
+  
+  /**Unique identification number.*/
+  val uid: Int = Shape.nextUid
+  
+  /**Flag determining this shapes ability to collide with other shapes.*/
+  var collidable: Boolean = true
+  
+  /**Part of the coefficient of restitution for a collision between this shape and another.
+   * The coefficient of restitution is calculated out of the product of this part and the other shape's part.*/
+  var restitution: Double = 0.7
+  
+  /**Part of the coefficient of friction for a collision between this shape and another.
+   * The coefficient of friction is calculated out of the product of this part and the other shape's part.*/
+  var friction: Double = 0.707
+  
+  /**Position of this shape's COM (in world coordinates).*/
+  var pos: Vector2D = Vector2D.Null
+  
+  /**Rotation of this shape about its COM.*/
+  var rotation: Double = 0
+  
+  /**Initial rotation. Rotation of this shape before it was added to a body.*/
+  var rotation0 = 0.0
+  
+  /**Local position of this shape's body COM to its COM at a body rotation of zero.*/
+  var refLocalPos: Vector2D = Vector2D.Null
+  
+  /**Density. (Mass per area)*/
+  val density: Double
+  
+  /**Volume. The volume is actually equivalent to this shape's area (SiMS is in 2D)
+   * and is used with this shape's density to calculate its mass.*/
+  val volume: Double
+  
+  /**Returns the mass of this shape. The mass is given by volume times density.
+   @return mass of this shape*/
+  def mass = volume * density
+  
+  /**Moment of inertia for a rotation about this shape's COM.*/
+  val I: Double
+  
+  /**Containing body.*/
+  private var _body: Body = _
+  
+  /**Returns this shape's containing body.*/
+  def body = _body
+  
+  /**Sets this shape's containing body.*/
+  private[dynamics] def body_=(b: Body) = _body = b
+  
+  /**Returns this shape's axis aligned bounding box.*/
+  def AABB: AABB
+  
+  /**Returns the projection of this shape onto the line given by the directional vector <code>axis</code>.
+   * @param axis directional vector of the line
+   * @return projection of this shape*/
+  def project(axis: Vector2D): Projection
+  
+  /**Checks if the point <code>point</code> is contained in this shape.*/
+  def contains(point: Vector2D): Boolean
+  
+  /**Creates a new body made out of tis shape.
+   @return a body made out of tis shape*/
+  def asBody = new Body(this)
+  
+  /**Shapes with which this shape cannot collide.*/
+  val transientShapes: collection.mutable.Set[Shape] = collection.mutable.Set()
+  
+  /**Creates a new body out of this shape and the shape <code>s</code>.*/
+  def ~(s: Shape) = new Body(this, s)
+  
+  /**Creates a new body out of this shape and the shapes of body <code>b</code>.*/
+  def ~(b: Body) = {
+    val shapes = this :: b.shapes
+    new Body(shapes: _*)
+  }
+}
+
+object Shape {
+  private var uidCounter = -1
+  private def nextUid = {uidCounter += 1; uidCounter}
+}