diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 3bbe2aa..cdf3cd9 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -7,7 +7,7 @@ cmake_minimum_required (VERSION 3.8)
 add_executable (GraviSim  
 	"main.cpp"
  "MainWindow.cpp"
-     "Screen.hpp" "Screen.cpp" "Planet.hpp" "Planet.cpp" "PlanetConfig.cpp" )
+     "Screen.hpp" "Screen.cpp" "Planet.hpp" "Planet.cpp" "PlanetConfig.cpp"  "PlanetManager.hpp" "PlanetManager.cpp")
 
 target_link_libraries(GraviSim
 	Qt5::Widgets
diff --git a/src/MainWindow.cpp b/src/MainWindow.cpp
index 0730a45..234c1ff 100644
--- a/src/MainWindow.cpp
+++ b/src/MainWindow.cpp
@@ -33,6 +33,7 @@ void MainWindow::OpenPlanetDialog(Planet* planet)
 	ui.config->Enable();
 	ui.config->SetTitle(planet->name);
 	ui.config->SetRadius(planet->radius);
+	ui.config->SetMass(planet->mass);
 	ui.config->SetColor(planet->GetColor());
 	ui.config->SetX(planet->position.rx());
 	ui.config->SetY(planet->position.ry());
@@ -48,10 +49,17 @@ void MainWindow::ClosePlanetDialog()
 	ui.config->Disable();
 	ui.config->SetColor(QColor(0, 0, 0, 0));
 	ui.config->SetRadius(0.f);
+	ui.config->SetMass(0.f);
 	ui.config->SetX(0.f);
 	ui.config->SetY(0.f);
 }
 
+void MainWindow::UpdatePlanetPositionInDialog(const QPointF& position)
+{
+	ui.config->SetX(position.x());
+	ui.config->SetY(position.y());
+}
+
 void MainWindow::OnNameChanged(const QString& name)
 {
 	if (activePlanet != nullptr)
@@ -64,6 +72,12 @@ void MainWindow::OnRadiusChanged(double radius)
 		activePlanet->radius = radius;
 }
 
+void MainWindow::OnMassChanged(double mass)
+{
+	if (activePlanet != nullptr)
+		activePlanet->mass = mass;
+}
+
 void MainWindow::OnColourChanged(const QColor& color)
 {
 	if (activePlanet != nullptr)
@@ -92,4 +106,5 @@ void MainWindow::OnToggle()
 {
 	isSimulating = !isSimulating;
 	ui.config->SetButtonLabel((isSimulating) ? "Stop Simulation" : "Start Simulation");
+	ui.screen->simulate = isSimulating;
 }
diff --git a/src/MainWindow.hpp b/src/MainWindow.hpp
index f705e5a..40639c2 100644
--- a/src/MainWindow.hpp
+++ b/src/MainWindow.hpp
@@ -17,9 +17,12 @@ public:
 	void OpenPlanetDialog(Planet* planet);
 	void ClosePlanetDialog();
 
+	void UpdatePlanetPositionInDialog(const QPointF& position);
+
 public slots:
 	void OnNameChanged(const QString& name);
 	void OnRadiusChanged(double radius);
+	void OnMassChanged(double mass);
 	void OnColourChanged(const QColor& color);
 	void OnXChanged(double x);
 	void OnYChanged(double y);
diff --git a/src/Planet.cpp b/src/Planet.cpp
index 069bb8b..9d31f0e 100644
--- a/src/Planet.cpp
+++ b/src/Planet.cpp
@@ -1,13 +1,18 @@
 #include "Planet.hpp"
 
-Planet::Planet(float xPos, float yPos, float radius, QColor color) :
-	position{ xPos, yPos }, radius(radius)
+#define LENGTH(v) (sqrtf(v.x()*v.x() + v.y()*v.y()))
+
+QPen Planet::arrowColor = QPen(Qt::white);
+QLine Planet::arrow = QLine();
+
+Planet::Planet(uint32_t id, float xPos, float yPos, float radius, QColor color) :
+	position{ xPos, yPos }, radius(radius), id(id)
 {
 	Initialize(color);
 }
 
-Planet::Planet(QPointF pos, float radius, QColor color) :
-	position(pos), radius(radius)
+Planet::Planet(uint32_t id, QPointF pos, float radius, QColor color) :
+	position(pos), radius(radius), id(id)
 {
 	Initialize(color);
 }
@@ -31,11 +36,33 @@ void Planet::SetColor(const QColor& color)
 	selectionColor = QColor::fromHsv((h + 180) % 360, s, v, a);
 }
 
-void Planet::Draw(QPainter* painter)
+void Planet::Update()
 {
-	painter->setBrush(circle);
-	painter->setPen(outline);
-	painter->drawEllipse(position, radius, radius);
+	velocity += acceleration * (1.f / 60.f);
+	position += velocity * (1.f / 60.f);
+}
+
+void Planet::Draw(QPainter & painter)
+{
+	painter.setBrush(circle);
+	painter.setPen(outline);
+	painter.drawEllipse(position, radius, radius);
+
+	// Draw velocity arrow
+	if (!velocity.isNull())
+	{
+		painter.save();
+		qreal angle = QPointF::dotProduct(velocity, QPointF(1.0f, 0.0f)) / LENGTH(velocity);
+		painter.rotate(angle);
+		
+		arrow.setP1(position.toPoint());
+		arrow.setP2((position + velocity).toPoint());
+
+		painter.setPen(arrowColor);
+		painter.drawLine(arrow);
+
+		painter.restore();
+	}
 }
 
 bool Planet::IsInside(QPointF point) const
@@ -48,4 +75,6 @@ void Planet::Initialize(QColor color)
 {
 	name = "Unnamed";
 	SetColor(color);
+	arrowColor.setWidthF(2.0f);
+	acceleration = QPointF(0.f, 0.f);
 }
diff --git a/src/Planet.hpp b/src/Planet.hpp
index 2b8d8a9..dec541b 100644
--- a/src/Planet.hpp
+++ b/src/Planet.hpp
@@ -7,8 +7,8 @@
 class Planet
 {
 public:
-	Planet(float xPos, float yPos, float radius, QColor color);
-	Planet(QPointF pos, float radius, QColor color);
+	Planet(uint32_t id, float xPos, float yPos, float radius, QColor color);
+	Planet(uint32_t id, QPointF pos, float radius, QColor color);
 
 	void Resize(float newRadius) { radius = newRadius; }
 	void Select(bool select);
@@ -16,7 +16,8 @@ public:
 	void SetColor(const QColor& color);
 	const QColor& GetColor() { return circle.color(); }
 
-	void Draw(QPainter* painter);
+	void Update();
+	void Draw(QPainter & painter);
 
 	bool IsInside(QPointF point) const;
 
@@ -24,9 +25,14 @@ private:
 	void Initialize(QColor color);
 
 public:
+	const uint32_t id;
+
 	QPointF position;
+	QPointF velocity;
+	QPointF acceleration;
 	QString name;
 	float radius;
+	float mass;
 
 private:
 
@@ -34,4 +40,7 @@ private:
 
 	QBrush circle;
 	QPen outline;
+
+	static QPen arrowColor;
+	static QLine arrow;
 };
\ No newline at end of file
diff --git a/src/PlanetConfig.cpp b/src/PlanetConfig.cpp
index fde0551..0ccb681 100644
--- a/src/PlanetConfig.cpp
+++ b/src/PlanetConfig.cpp
@@ -18,6 +18,9 @@ PlanetConfig::PlanetConfig(QWidget* parent) :
 	connect(ui.radius, QOverload<double>::of(&QDoubleSpinBox::valueChanged),
 		instance, [instance](double d) { instance->OnRadiusChanged(d); });
 
+	connect(ui.mass, QOverload<double>::of(&QDoubleSpinBox::valueChanged),
+		instance, [instance](double d) { instance->OnMassChanged(d); });
+
 	connect(ui.colour, SIGNAL(returnPressed()),
 		this, SLOT(ColourTBSlot()));
 
@@ -38,6 +41,7 @@ PlanetConfig::PlanetConfig(QWidget* parent) :
 void PlanetConfig::Disable()
 {
 	ui.radius->setDisabled(true);
+	ui.mass->setDisabled(true);
 	ui.colour->setDisabled(true);
 	ui.xPos->setDisabled(true);
 	ui.yPos->setDisabled(true);
@@ -47,6 +51,7 @@ void PlanetConfig::Disable()
 void PlanetConfig::Enable()
 {
 	ui.radius->setDisabled(false);
+	ui.mass->setDisabled(false);
 	ui.colour->setDisabled(false);
 	ui.xPos->setDisabled(false);
 	ui.yPos->setDisabled(false);
@@ -78,6 +83,11 @@ void PlanetConfig::SetY(double y)
 	ui.yPos->setValue(y);
 }
 
+void PlanetConfig::SetMass(double mass)
+{
+	ui.mass->setValue(mass);
+}
+
 void PlanetConfig::SetButtonLabel(const QString& label)
 {
 	ui.toggle->setText(label);
diff --git a/src/PlanetConfig.hpp b/src/PlanetConfig.hpp
index 4f21ae2..d1f594d 100644
--- a/src/PlanetConfig.hpp
+++ b/src/PlanetConfig.hpp
@@ -19,6 +19,7 @@ public:
 	void SetColor(const QColor& color);
 	void SetX(double x);
 	void SetY(double y);
+	void SetMass(double mass);
 
 	void SetButtonLabel(const QString& label);
 
diff --git a/src/PlanetManager.cpp b/src/PlanetManager.cpp
new file mode 100644
index 0000000..97ea9be
--- /dev/null
+++ b/src/PlanetManager.cpp
@@ -0,0 +1,99 @@
+#include "PlanetManager.hpp"
+
+std::map<uint32_t, Planet*> PlanetManager::planets;
+uint32_t PlanetManager::planetCounter = 0;
+
+Planet* PlanetManager::AddPlanet(const QPointF& position, float radius, const QColor& color, const QString& name)
+{
+	Planet* planet = new Planet(planetCounter, position, radius, color);
+	planet->mass = rand() % 100;
+
+	planets.insert(
+		std::make_pair(
+			planetCounter++,
+			planet
+		)
+	);
+
+	return planet;
+}
+
+void PlanetManager::RemovePlanet(uint32_t id)
+{
+	auto it = planets.find(id);
+	if (it == planets.end())
+		return;
+
+	delete it->second;
+	planets.erase(it);
+}
+
+Planet* PlanetManager::GetPlanet(uint32_t id)
+{
+	auto it = planets.find(id);
+	if (it == planets.end())
+		return nullptr;
+	return it->second;
+}
+
+Planet* PlanetManager::GetLastPlanet()
+{
+	return planets.rbegin()->second;
+}
+
+void PlanetManager::RemoveLastPlanet()
+{
+	auto it = planets.cbegin();
+	delete it->second;
+
+	planets.erase(it);
+}
+
+Planet* PlanetManager::IsInPlanet(const QPointF& position)
+{
+	for (auto it : planets)
+		if (it.second->IsInside(position))
+			return it.second;
+	
+	return nullptr;
+}
+
+void PlanetManager::Update()
+{
+	for (auto planet : planets)
+		planet.second->Update();
+
+	// Collision detection && Gravitation
+	for (auto planet : planets)
+	{
+		planet.second->acceleration = QPointF(0.f, 0.f);
+		for (auto otherPlanet : planets)
+		{
+			if (planet == otherPlanet)
+				continue;
+
+			QPointF distance = planet.second->position - otherPlanet.second->position;
+			float radiusSum = (planet.second->radius + otherPlanet.second->radius);
+			float dist = distance.x() * distance.x() + distance.y() * distance.y();
+			if (dist < radiusSum * radiusSum)
+			{
+				// Collision
+				Planet* lighter = ((planet.second->mass > otherPlanet.second->mass) ? otherPlanet.second : planet.second);
+				lighter->position += (radiusSum - sqrt(dist) + 1) * distance / sqrt(dist);
+			}
+			else
+			{
+				// Gravitation
+				planet.second->acceleration -= 1000000 * (planet.second->mass * otherPlanet.second->mass) / pow(dist, 3.f / 2.f) * distance / sqrt(dist);
+			}
+		}
+
+		planet.second->acceleration /= planet.second->mass;
+	}
+}
+
+void PlanetManager::Render(QPainter& painter)
+{
+	for (auto it : planets)
+		it.second->Draw(painter);
+}
diff --git a/src/PlanetManager.hpp b/src/PlanetManager.hpp
new file mode 100644
index 0000000..05698a2
--- /dev/null
+++ b/src/PlanetManager.hpp
@@ -0,0 +1,30 @@
+#pragma once
+
+#include <map>
+
+#include <QPointF>
+
+#include "Planet.hpp"
+
+class PlanetManager
+{
+public:
+	PlanetManager() = delete;
+
+	static Planet* AddPlanet(const QPointF& position, float radius, const QColor& color, 
+		const QString& name = "Unnamed");
+	static void RemovePlanet(uint32_t id);
+
+	static Planet* GetPlanet(uint32_t id);
+	static Planet* GetLastPlanet();
+	static void RemoveLastPlanet();
+
+	static Planet* IsInPlanet(const QPointF& position);
+
+	static void Update();
+	static void Render(QPainter& painter);
+
+private:
+	static std::map<uint32_t, Planet*> planets;
+	static uint32_t planetCounter;
+};
\ No newline at end of file
diff --git a/src/Screen.cpp b/src/Screen.cpp
index 0a56524..61d2953 100644
--- a/src/Screen.cpp
+++ b/src/Screen.cpp
@@ -9,6 +9,7 @@
 #include <QtMath>
 
 #include "MainWindow.hpp"
+#include "PlanetManager.hpp"
 
 #define BIND_LMB(f) (lmbAction = std::bind(&Screen::f, this, std::placeholders::_1))
 
@@ -32,32 +33,30 @@ Screen::Screen(QWidget* parent) :
 
 void Screen::mouseMoveEvent(QMouseEvent* event)
 {
-	if (mouseDown && hovered == nullptr)
+	if (mouseDown && selected == nullptr && hovered == nullptr)
 	{
-		Planet* planet = planets.back();
+		Planet* planet = PlanetManager::GetLastPlanet();
 		QPointF distance = event->localPos() - mouseClickPos;
 		planet->Resize(qSqrt(distance.x()*distance.x() + distance.y() *distance.y()));
 	}
+	else if (mouseDown && selected != nullptr)
+	{
+		selected->velocity = event->localPos() - selected->position;
+	}
 	else
 	{
-		hovered = nullptr;
-		for (unsigned i = planets.size(); i-- > 0; )
-		{
-			if (planets[i]->IsInside(event->localPos()))
-			{
-				setCursor(Qt::PointingHandCursor);
-				BIND_LMB(lmb_SelectPlanet);
-				hovered = planets[i];
-				break;
-			}
-		}
-
+		hovered = PlanetManager::IsInPlanet(event->localPos());
 		if (hovered == nullptr)
 		{
 			setCursor(Qt::ArrowCursor);
 			if(selected == nullptr)
 				BIND_LMB(lmb_MakePlanet);
 		}
+		else
+		{
+			BIND_LMB(lmb_SelectPlanet);
+			setCursor(Qt::PointingHandCursor);
+		}
 	}
 }
 
@@ -72,7 +71,7 @@ void Screen::mousePressEvent(QMouseEvent* event)
 	{
 		if (mouseDown)
 		{
-			planets.pop_back();
+			PlanetManager::RemoveLastPlanet();
 			mouseDown = false;
 		}
 	}
@@ -86,17 +85,9 @@ void Screen::mouseReleaseEvent(QMouseEvent* event)
 
 void Screen::DeletePlanet(Planet* planet)
 {
-	for (std::vector<Planet*>::iterator it = planets.begin(); it != planets.end(); it++)
-	{
-		if ((*it) == planet)
-		{
-			planets.erase(it);
-			delete planet;
-			hovered = nullptr;
-			selected = nullptr;
-			break;
-		}
-	}
+	PlanetManager::RemovePlanet(planet->id);
+	hovered = nullptr;
+	selected = nullptr;
 }
 
 void Screen::Render()
@@ -106,9 +97,12 @@ void Screen::Render()
 
 void Screen::lmb_MakePlanet(QMouseEvent* event)
 {
-	planets.push_back(new Planet(event->localPos(), 0,
-		QColor(rand() % 256, rand() % 256, rand() % 256)
-	));
+	Planet* newPlanet = PlanetManager::AddPlanet(event->localPos(), 0,
+		QColor(rand() % 200, rand() % 200, rand() % 200)
+	);
+
+	newPlanet->velocity = QPointF(rand() % 400 - 200, rand() % 400 - 200);
+
 	mouseClickPos = event->localPos();
 	mouseDown = true;
 }
@@ -117,12 +111,19 @@ void Screen::lmb_SelectPlanet(QMouseEvent* event)
 {
 	if (hovered != nullptr)
 	{
-		if (selected != nullptr)
-			selected->Select(false);
+		if (selected != hovered)
+		{
+			if (selected != nullptr)
+				selected->Select(false);
 
-		hovered->Select(true);
-		selected = hovered;
-		MainWindow::Instance()->OpenPlanetDialog(selected);
+			hovered->Select(true);
+			selected = hovered;
+			MainWindow::Instance()->OpenPlanetDialog(selected);
+		}
+		else
+		{
+			mouseDown = true;
+		}
 	}
 	else
 	{
@@ -136,12 +137,20 @@ void Screen::lmb_SelectPlanet(QMouseEvent* event)
 
 void Screen::paintEvent(QPaintEvent* event)
 {
+	if (simulate)
+	{
+		PlanetManager::Update();
+		if (selected != nullptr)
+		{
+			MainWindow::Instance()->UpdatePlanetPositionInDialog(selected->position);
+		}
+	}
+
 	QPainter painter;
 	painter.begin(this);
 	painter.fillRect(rect(), background);
 
-	for (Planet* planet : planets)
-		planet->Draw(&painter);
+	PlanetManager::Render(painter);
 
 	painter.end();
 }
\ No newline at end of file
diff --git a/src/Screen.hpp b/src/Screen.hpp
index 50b5dad..d93be25 100644
--- a/src/Screen.hpp
+++ b/src/Screen.hpp
@@ -5,8 +5,8 @@
 
 #include <QOpenGLWidget>
 
-#include "Planet.hpp"
 
+class Planet;
 class MainWindow;
 
 class Screen : public QOpenGLWidget
@@ -30,6 +30,9 @@ private:
 protected:
 	void paintEvent(QPaintEvent* event) override;
 
+public:
+	bool simulate = false;
+
 private:
 	bool mouseDown = false;
 
@@ -40,7 +43,6 @@ private:
 	QBrush background;
 	QTimer* renderTimer;
 
-	std::vector<Planet*> planets;
 	Planet* selected = nullptr;
 	Planet* hovered = nullptr;
 };
\ No newline at end of file
diff --git a/ui/PlanetConfig.ui b/ui/PlanetConfig.ui
index eedd0ac..9d22ae1 100644
--- a/ui/PlanetConfig.ui
+++ b/ui/PlanetConfig.ui
@@ -7,7 +7,7 @@
     <x>0</x>
     <y>0</y>
     <width>308</width>
-    <height>380</height>
+    <height>454</height>
    </rect>
   </property>
   <property name="windowTitle">
@@ -82,6 +82,42 @@
        </item>
       </layout>
      </item>
+     <item>
+      <layout class="QHBoxLayout" name="horizontalLayout_2">
+       <item>
+        <widget class="QLabel" name="label_2">
+         <property name="font">
+          <font>
+           <family>Courier New</family>
+           <pointsize>12</pointsize>
+          </font>
+         </property>
+         <property name="text">
+          <string>Mass</string>
+         </property>
+         <property name="alignment">
+          <set>Qt::AlignRight|Qt::AlignTrailing|Qt::AlignVCenter</set>
+         </property>
+        </widget>
+       </item>
+       <item>
+        <widget class="QDoubleSpinBox" name="mass">
+         <property name="styleSheet">
+          <string notr="true">background-color: rgb(255, 255, 255);</string>
+         </property>
+         <property name="maximum">
+          <double>1000.000000000000000</double>
+         </property>
+         <property name="singleStep">
+          <double>1.000000000000000</double>
+         </property>
+         <property name="stepType">
+          <enum>QAbstractSpinBox::AdaptiveDecimalStepType</enum>
+         </property>
+        </widget>
+       </item>
+      </layout>
+     </item>
      <item>
       <layout class="QHBoxLayout" name="horizontalLayout_3">
        <item>