diff --git a/src/net/torvald/terrarum/Game.kt b/src/net/torvald/terrarum/Game.kt
index 75b593a9c..c221842f0 100644
--- a/src/net/torvald/terrarum/Game.kt
+++ b/src/net/torvald/terrarum/Game.kt
@@ -3,7 +3,7 @@ package net.torvald.terrarum
 import net.torvald.imagefont.GameFontBase
 import net.torvald.terrarum.gameactors.*
 import net.torvald.terrarum.console.Authenticator
-import net.torvald.terrarum.gameactors.collisionsolver.CollisionSolver
+import net.torvald.terrarum.gameactors.physicssolver.CollisionSolver
 import net.torvald.terrarum.gamecontroller.GameController
 import net.torvald.terrarum.gamecontroller.Key
 import net.torvald.terrarum.gamecontroller.KeyMap
diff --git a/src/net/torvald/terrarum/gameactors/ActorWithBody.kt b/src/net/torvald/terrarum/gameactors/ActorWithBody.kt
index 430e22592..516ef959d 100644
--- a/src/net/torvald/terrarum/gameactors/ActorWithBody.kt
+++ b/src/net/torvald/terrarum/gameactors/ActorWithBody.kt
@@ -8,6 +8,7 @@ import net.torvald.terrarum.tileproperties.TilePropCodex
 import net.torvald.spriteanimation.SpriteAnimation
 import com.jme3.math.FastMath
 import net.torvald.terrarum.tileproperties.TileNameCode
+import org.dyn4j.geometry.Vector2
 import org.newdawn.slick.GameContainer
 import org.newdawn.slick.Graphics
 
@@ -31,8 +32,13 @@ open class ActorWithBody constructor() : Actor(), Visible {
      *     veloY += 3.0
      * +3.0 is acceleration. You __accumulate__ acceleration to the velocity.
      */
-    @Volatile var veloX: Double = 0.0
-    @Volatile var veloY: Double = 0.0
+    val velocity = Vector2(0.0, 0.0)
+    var veloX: Double
+        get() = velocity.x
+        set(value) { velocity.set(value, veloY) }
+    var veloY: Double
+        get() = velocity.y
+        set(value) { velocity.set(veloX, value) }
     @Transient private val VELO_HARD_LIMIT = 10000.0
 
     var grounded = false
@@ -62,8 +68,11 @@ open class ActorWithBody constructor() : Actor(), Visible {
      * Physical properties.
      * Values derived from ActorValue must be @Transient.
      */
-    @Transient var scale = 1.0
-    @Transient var mass = 2.0
+    var scale: Double
+        get() = actorValue.getAsDouble(AVKey.SCALE) ?: 1.0
+        set(value) = actorValue.set(AVKey.SCALE, value)
+    val mass: Double
+        get() = actorValue.getAsDouble(AVKey.BASEMASS) ?: MASS_DEFAULT * Math.pow(scale, 3.0)
     @Transient private val MASS_LOWEST = 2.0
     /** Valid range: [0, 1]  */
     var elasticity = 0.0
@@ -140,6 +149,10 @@ open class ActorWithBody constructor() : Actor(), Visible {
 
     @Transient private val BASE_FRICTION = 0.3
 
+    @Transient val KINEMATIC = 1
+    @Transient val DYNAMIC = 2
+    @Transient val STATIC = 3
+
     init {
         map = Terrarum.game.map
     }
@@ -184,20 +197,10 @@ open class ActorWithBody constructor() : Actor(), Visible {
                 baseHitboxH * scale)
     }
 
-    private fun updatePhysicalInfos() {
-        scale = actorValue.getAsDouble(AVKey.SCALE) ?: 1.0
-        mass = (actorValue.getAsDouble(AVKey.BASEMASS) ?: MASS_DEFAULT) * Math.pow(scale, 3.0)
-        if (elasticity != 0.0) elasticity = 0.0
-    }
-
     override fun run() = update(Terrarum.appgc, Terrarum.game.DELTA_T)
 
     override fun update(gc: GameContainer, delta_t: Int) {
         if (isUpdate) {
-            /**
-             * Update variables
-             */
-            updatePhysicalInfos()
 
             // make NoClip work for player
             if (this is Player) {
@@ -206,9 +209,6 @@ open class ActorWithBody constructor() : Actor(), Visible {
                 isNoSubjectToFluidResistance = isPlayerNoClip
             }
 
-            // clamp to the minimum possible mass
-            if (mass < MASS_LOWEST) mass = MASS_LOWEST
-
             // set sprite dimension vars if there IS sprite for the actor
             if (sprite != null) {
                 baseSpriteHeight = sprite!!.height
diff --git a/src/net/torvald/terrarum/gameactors/Hitbox.kt b/src/net/torvald/terrarum/gameactors/Hitbox.kt
index dd6d9e29f..5b4ba89e1 100644
--- a/src/net/torvald/terrarum/gameactors/Hitbox.kt
+++ b/src/net/torvald/terrarum/gameactors/Hitbox.kt
@@ -47,7 +47,7 @@ class Hitbox(x1: Double, y1: Double, width: Double, height: Double) {
      * *
      * @param height
      */
-    operator fun set(x1: Double, y1: Double, width: Double, height: Double) {
+    fun set(x1: Double, y1: Double, width: Double, height: Double) {
         hitboxStart = Point2d(x1, y1)
         hitboxEnd = Point2d(x1 + width, y1 + height)
         this.width = width
diff --git a/src/net/torvald/terrarum/gameactors/collisionsolver/CollisionSolver.kt b/src/net/torvald/terrarum/gameactors/physicssolver/CollisionSolver.kt
similarity index 99%
rename from src/net/torvald/terrarum/gameactors/collisionsolver/CollisionSolver.kt
rename to src/net/torvald/terrarum/gameactors/physicssolver/CollisionSolver.kt
index 95e9fe2cb..c5baccbba 100644
--- a/src/net/torvald/terrarum/gameactors/collisionsolver/CollisionSolver.kt
+++ b/src/net/torvald/terrarum/gameactors/physicssolver/CollisionSolver.kt
@@ -1,4 +1,4 @@
-package net.torvald.terrarum.gameactors.collisionsolver
+package net.torvald.terrarum.gameactors.physicssolver
 
 import com.jme3.math.FastMath
 import net.torvald.terrarum.Terrarum
diff --git a/src/net/torvald/terrarum/gameactors/collisionsolver/SolveByUnit.kt b/src/net/torvald/terrarum/gameactors/physicssolver/SolveByUnit.kt
similarity index 80%
rename from src/net/torvald/terrarum/gameactors/collisionsolver/SolveByUnit.kt
rename to src/net/torvald/terrarum/gameactors/physicssolver/SolveByUnit.kt
index 7a94529ce..9183282ff 100644
--- a/src/net/torvald/terrarum/gameactors/collisionsolver/SolveByUnit.kt
+++ b/src/net/torvald/terrarum/gameactors/physicssolver/SolveByUnit.kt
@@ -1,4 +1,4 @@
-package net.torvald.terrarum.gameactors.collisionsolver
+package net.torvald.terrarum.gameactors.physicssolver
 
 /**
  * multithreaded version of CollisionSolver#solveCollision
diff --git a/src/net/torvald/terrarum/gameactors/physicssolver/VelocitySolver.kt b/src/net/torvald/terrarum/gameactors/physicssolver/VelocitySolver.kt
new file mode 100644
index 000000000..651f7dd9e
--- /dev/null
+++ b/src/net/torvald/terrarum/gameactors/physicssolver/VelocitySolver.kt
@@ -0,0 +1,18 @@
+package net.torvald.terrarum.gameactors.physicssolver
+
+import net.torvald.terrarum.gameactors.ActorWithBody
+
+/**
+ * Created by minjaesong on 16-05-01.
+ */
+object VelocitySolver {
+
+    fun process() {
+
+    }
+
+    private fun applyGravity(actor: ActorWithBody) {
+
+    }
+
+}
\ No newline at end of file