diff --git a/ToyEngine/src/DemoWorld.cpp b/ToyEngine/src/DemoWorld.cpp
index db2f71d..09a3d7c 100644
--- a/ToyEngine/src/DemoWorld.cpp
+++ b/ToyEngine/src/DemoWorld.cpp
@@ -21,27 +21,58 @@ DemoWorld::DemoWorld()
 	auto sponza = std::make_shared<Actor>("Models\\Sponza\\Sponza.gltf");
 	sponza->setScale(glm::vec3(2));
 
-	auto particle = std::make_shared<Particle>(10);
-	particle->setSpeed(glm::vec3(-1, 0, 0));
-	particle->setPosition({ 4, 5, 0 });
-	//particle->addForce(std::make_shared<Force>(glm::vec3(0.f, -particle->getMass() * 9.8f, 0.f)));
-	auto particle2 = std::make_shared<Particle>(10, "Models\\pallet_wood\\pallet_wood.gltf");
-	particle2->setSpeed(glm::vec3(1, 0, 0));
-	particle2->setPosition({ 6, 5, 0 });
-	particle2->setScale(glm::vec3{ 0.002 });
-
-	auto particle3 = std::make_shared<Particle>(10);
-	particle3->setSpeed(glm::vec3(0, 1, 0));
-	particle3->setPosition({ 6, 7, 0 });
-
-	physicsManager.addSpring(particle, particle2, 2, 10, 0);
-	physicsManager.addSpring(particle2, particle3, 2, 10, 0);
-
 	addActor(actor);
 	addActor(actor2);
 	addActor(actor3);
 	addActor(sponza);
-	addActor(particle);
-	addActor(particle2);
-	addActor(particle3);
+
+
+	float boardMass = 10;
+	glm::vec3 boardScale(0.01);
+	auto boardFilePath = "Models\\pallet_wood\\pallet_wood.gltf";
+
+
+	int particleCount = 5;
+	for (int i = 0; i < particleCount; i++)
+	{
+		auto particle = std::make_shared<Particle>(boardMass, boardFilePath);
+		particle->setPosition({ 0, 8, glm::mix(-3.1f,2.f,(double)i / (particleCount - 1)) });
+		particle->setScale(boardScale);
+		if (i == 0 || i == particleCount - 1)
+		{
+			particle->setFixed(true);
+		}
+		else
+		{
+			particle->enableGravity();
+		}
+		particles.push_back(particle);
+		addActor(particle);
+
+		if (i != 0)
+		{
+			float ks = 300, kd = 100;
+			physicsManager.addSpring(particles[i - 1], particle, 0.005, ks, kd);
+		}
+	}
+}
+
+void DemoWorld::logicalTick(float deltaTime)
+{
+	World::logicalTick(deltaTime);
+	for (int i = 0; i < particles.size(); i++)
+	{
+		glm::vec3 d;
+		if (i == 0)
+			d = glm::normalize(particles[i + 1]->getPosition() - particles[i]->getPosition());
+		else if (i == particles.size() - 1)
+			d = glm::normalize(particles[i]->getPosition() - particles[i - 1]->getPosition());
+		else
+		{
+			auto dL = particles[i + 1]->getPosition() - particles[i]->getPosition();
+			auto dR = particles[i]->getPosition() - particles[i - 1]->getPosition();
+			d = (glm::normalize(dL) + glm::normalize(dR)) / 2.f;
+		}
+		particles[i]->setRotaion(glm::rotation(glm::vec3(0, 0, 1), d));
+	}
 }
diff --git a/ToyEngine/src/DemoWorld.h b/ToyEngine/src/DemoWorld.h
index 896fc19..9f949d2 100644
--- a/ToyEngine/src/DemoWorld.h
+++ b/ToyEngine/src/DemoWorld.h
@@ -5,5 +5,8 @@ class DemoWorld : public World
 {
 public:
 	DemoWorld();
+	virtual void logicalTick(float deltaTime) override;
+private:
+	std::vector<std::shared_ptr<Particle>> particles;
 };
 
diff --git a/ToyEngine/src/Particle.cpp b/ToyEngine/src/Particle.cpp
index a849ff0..b852d9f 100644
--- a/ToyEngine/src/Particle.cpp
+++ b/ToyEngine/src/Particle.cpp
@@ -23,13 +23,22 @@ void Particle::logicalTick(float deltaTime)
 	for (auto& force : forces)
 		resultantForce += force->value;
 
-	auto pos = getPosition() + speed * deltaTime + 0.5f * resultantForce / mass * deltaTime * deltaTime;
-	speed += resultantForce / mass * deltaTime;
-	//if (speed.y < 0 && pos.y < 0.4)
-	//{
-	//	speed.y = -speed.y;
-	//}
-	setPosition(pos);
+	if (fixed)
+	{
+		speed = glm::vec3(0);
+	}
+	else
+	{
+		//auto pos = getPosition() + speed * deltaTime + 0.5f * resultantForce / mass * deltaTime * deltaTime;
+		speed += resultantForce / mass * deltaTime;
+		auto pos = getPosition() + speed * deltaTime;
+		//if (speed.y < 0 && pos.y < 0.4)
+		//{
+		//	speed.y = -speed.y;
+		//}
+		setPosition(pos);
+	}
+
 }
 
 void Particle::draw(const RenderPassContext& context, Shader& shader)
@@ -57,9 +66,10 @@ void Particle::draw(const RenderPassContext& context, Shader& shader)
 		}
 
 		debugShader.use();
+		gl->DepthMask(false);
 		debugShader.setUniformValue("projection", *context.projection);
 		debugShader.setUniformValue("view", *context.view);
-		glm::mat4 modelMatrix = glm::translate(glm::mat4(1), getPosition()) * glm::mat4_cast(getRotation()) * glm::scale(glm::mat4(1), glm::vec3(glm::abs(resultantForce / mass)));
+		glm::mat4 modelMatrix = glm::translate(glm::mat4(1), getPosition());// *glm::scale(glm::mat4(1), glm::vec3(glm::abs(resultantForce / mass)));
 		gl->BindVertexArray(vao);
 		for (auto& force : forces)
 		{
@@ -68,6 +78,7 @@ void Particle::draw(const RenderPassContext& context, Shader& shader)
 			gl->DrawArrays(GL_LINES, 0, 2);
 		}
 		gl->BindVertexArray(0);
+		gl->DepthMask(true);
 		shader.use();
 	}
 }
@@ -96,3 +107,13 @@ void Particle::setSpeed(const glm::vec3& speed)
 {
 	this->speed = speed;
 }
+
+void Particle::setFixed(bool fixed)
+{
+	this->fixed = fixed;
+}
+
+void Particle::enableGravity()
+{
+	addForce(std::make_shared<Force>(glm::vec3(0.f, -getMass() * 9.80665f, 0.f)));
+}
diff --git a/ToyEngine/src/Particle.h b/ToyEngine/src/Particle.h
index 2a05193..9889eea 100644
--- a/ToyEngine/src/Particle.h
+++ b/ToyEngine/src/Particle.h
@@ -21,8 +21,12 @@ public:
 	float getMass();
 	glm::vec3 getSpeed();
 	void setSpeed(const glm::vec3& speed);
+	void setFixed(bool fixed);
+	void enableGravity();
 private:
+	bool fixed = false;
 	float mass;
+	glm::vec3 acceleration = glm::vec3(0);
 	glm::vec3 speed = glm::vec3(0.f);
 	std::set<std::shared_ptr<Force>> forces;
 	glm::vec3 resultantForce = glm::vec3(0);
diff --git a/ToyEngine/src/PhysicsManager.cpp b/ToyEngine/src/PhysicsManager.cpp
index 96af01c..996f040 100644
--- a/ToyEngine/src/PhysicsManager.cpp
+++ b/ToyEngine/src/PhysicsManager.cpp
@@ -25,6 +25,7 @@ void PhysicsManager::addSpring(std::shared_ptr<Particle> p1, std::shared_ptr<Par
 		auto d = glm::distance(p1.getPosition(), p2.getPosition());
 		float dt = 1.f;
 		auto vd = glm::distance(p1.getPosition() + p1.getSpeed() * dt, p2.getPosition() + p2.getSpeed() * dt) / dt;
+		if (d == 0) return glm::vec3(0);
 		return -(ks * (d - length) + kd * vd) * (p1.getPosition() - p2.getPosition()) / d;
 		}, f1, f2);
 }