diff --git a/api/api.lua b/api/api.lua
index 5262e30..de9b443 100644
--- a/api/api.lua
+++ b/api/api.lua
@@ -524,4 +524,60 @@ function better_fauna.on_activate(self, staticdata, dtime_s)
     self.breeding = mobkit.recall(self, "breeding") or false
     self.breeding_time = mobkit.recall(self, "breeding_time") or 0
     self.breeding_cooldown = mobkit.recall(self, "breeding_cooldown") or 0
-end
\ No newline at end of file
+end
+
+-------------
+-- Physics --
+-------------
+
+function better_fauna.lightweight_physics(self)
+	local vel = self.object:get_velocity()
+	if self.isonground and not self.isinliquid then
+		self.object:set_velocity({x= vel.x> 0.2 and vel.x*mobkit.friction or 0,
+								y=vel.y,
+								z=vel.z > 0.2 and vel.z*mobkit.friction or 0})
+	end
+	if self.springiness and self.springiness > 0 then
+		local vnew = vector.new(vel)
+		
+		if not self.collided then
+			for _,k in ipairs({'y','z','x'}) do			
+				if vel[k]==0 and abs(self.lastvelocity[k])> 0.1 then 
+					vnew[k]=-self.lastvelocity[k]*self.springiness 
+				end
+			end
+		end
+		if not vector.equals(vel,vnew) then
+			self.collided = true
+		else
+			if self.collided then
+				vnew = vector.new(self.lastvelocity)
+			end
+			self.collided = false
+		end
+		
+		self.object:set_velocity(vnew)
+	end
+	local surface = nil
+	local surfnodename = nil
+	local spos = mobkit.get_stand_pos(self)
+	spos.y = spos.y+0.01
+	local snodepos = mobkit.get_node_pos(spos)
+	local surfnode = mobkit.nodeatpos(spos)
+	while surfnode and surfnode.drawtype == 'liquid' do
+		surfnodename = surfnode.name
+		surface = snodepos.y+0.5
+		if surface > spos.y+self.height then break end
+		snodepos.y = snodepos.y+1
+		surfnode = mobkit.nodeatpos(snodepos)
+	end
+	self.isinliquid = surfnodename
+	if surface then
+		local submergence = min(surface-spos.y,self.height)/self.height
+		local buoyacc = mobkit.gravity*(self.buoyancy-submergence)
+		mobkit.set_acceleration(self.object,
+			{x=-vel.x*self.water_drag,y=buoyacc-vel.y*abs(vel.y)*0.4,z=-vel.z*self.water_drag})
+	else
+		self.object:set_acceleration({x=0,y=-2.8,z=0})
+	end
+end