diff --git a/src/play_clj/core_physics.clj b/src/play_clj/core_physics.clj
index e9a81b1..1e4bdaf 100644
--- a/src/play_clj/core_physics.clj
+++ b/src/play_clj/core_physics.clj
@@ -6,11 +6,14 @@
   (fn [screen & [entities]] (-> screen (u/get-obj :world) class)))
 
 (defmulti add-body!
-  "Adds the `body` to the `screen` for physics simulations and returns it."
+  "Adds the `body` to the `screen` for physics simulations and returns it. For
+2D physics, `body` should be a `body-def`, whereas for 3D physics it should be a
+`basic-body` or a `rigid-body`."
   (fn [screen body] (-> screen (u/get-obj :world) class)))
 
 (defmulti body-position!
-  "Changes the position of the body in `entity`."
+  "Changes the position of the body in `entity`. For 2D physics, the arguments
+should be x, y, and angle, whereas for 3D physics they should be x, y, and z."
   (fn [entity a1 a2 a3] (-> entity (u/get-obj :body) class)))
 
 (defmulti body-x!
@@ -22,9 +25,9 @@
   (fn [entity y] (-> entity (u/get-obj :body) class)))
 
 (defmulti body-z!
-  "Changes the `z` of the body in `entity`."
+  "Changes the `z` of the body in `entity`. Only works with 3D physics."
   (fn [entity z] (-> entity (u/get-obj :body) class)))
 
 (defmulti body-angle!
-  "Changes the `angle` of the body in `entity`."
+  "Changes the `angle` of the body in `entity`. Only works with 2D physics."
   (fn [entity angle] (-> entity (u/get-obj :body) class)))