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diff --git a/slideshow/README b/slideshow/README
index e523458531ae..e67379f43c89 100644
@@ -8,3 +8,36 @@ written by GSOC student Shane.M.Mathews. Radek has later polished the
code a bit, added few new 3D transitions, added infrastructure for
vertex and fragment shaders. Wrote few transitions with fragment shader
+== Physics Animation Effects ==
+Physics animation effects are simulated by external 2d physics engine
+library Box2D. They don't directly call Box2D functions but instead
+use the wrapper in:
+The wrapper has two corresponding classes to manage the Box2D world
+and Box2D bodies.
+When a physics animation starts, a Box2DWorld is initiated and
+populated with every shape that is part of the foreground (which are
+shapes that do not belong to the master slide and not a background
+After creation until the end of the slide (not the whole slideshow)
+the Box2D World isn't destroyed and reused. But the bodies that
+represent the shapes in the slide get destroyed when there's a point
+in time that there's no physics animation in progress. And recreated
+when another physics animation starts.
+If there are multiple physics animations in parallel only one of them
+takes the role of stepping through the simulation.
+If there are other animation effects that go in parallel which change
+the shape position, rotation, or visibility - they also report the
+change to Box2D World. These updates are collected in a queue in
+Box2DWorld and processed before stepping through the simulation.
+To achieve convincing results these updates are performed by setting
+the box2d body's linear velocity or angular velocity instead of
+setting directly it's position or rotation.