diff --git a/Shader/particle_update.gs b/Shader/particle_update.gs
index 6627ca4..4976da3 100644
--- a/Shader/particle_update.gs
+++ b/Shader/particle_update.gs
@@ -29,7 +29,7 @@ uniform vec3 spawn_color;
 uniform float spawn_size; 
 
 uniform float spawn_lifetime_min, spawn_lifetime_range; // Life of new particle - from min to (min+range)
-uniform float time_passed; // Time passed since last frame
+uniform float delta; // Time passed since last frame
 
 uniform vec3 random_seed; // Seed number for our random number function
 vec3 local_seed;
@@ -55,11 +55,11 @@ void main() {
   position_out = position_pass[0];
   velocity_out = velocity_pass[0];
 
-  if(type_pass[0] != 0.0) position_out += velocity_out * time_passed;
-  if(type_pass[0] != 0.0) velocity_out += spawn_gravity * time_passed;
+  if(type_pass[0] != 0.0) position_out += velocity_out * delta;
+  if(type_pass[0] != 0.0) velocity_out += spawn_gravity * delta;
 
   color_out = color_pass[0];
-  lifetime_out = lifetime_pass[0] - time_passed;
+  lifetime_out = lifetime_pass[0] - delta;
   size_out = size_pass[0];
   type_out = type_pass[0];
     
diff --git a/cpp/ParticleSystem.cpp b/cpp/ParticleSystem.cpp
index d1a70a4..d3c4612 100644
--- a/cpp/ParticleSystem.cpp
+++ b/cpp/ParticleSystem.cpp
@@ -52,7 +52,7 @@ ParticleSystem::ParticleSystem() {
 void ParticleSystem::update(float delta) {
     update_shader.use();
 
-    update_shader.setFloat("time_passed", elapsed_time);
+    update_shader.setFloat("delta", delta);
     update_shader.setVec3("spawn_position", spawn_position);
     update_shader.setVec3("spawn_velocity_min", spawn_velocity_min);
     update_shader.setVec3("spawn_velocity_range", spawn_velocity_range);
diff --git a/test/particle-demo/main.cpp b/test/particle-demo/main.cpp
index 17fbeab..0600932 100644
--- a/test/particle-demo/main.cpp
+++ b/test/particle-demo/main.cpp
@@ -1,3 +1,4 @@
+#include "Gedeng/Input.h"
 #include "Gedeng/Logger.h"
 #include "Gedeng/ParticleSystem.h"
 #include "Gedeng/QuadMesh.h"
@@ -11,8 +12,8 @@ class ParticleApp : public Gedeng::Application {
   public:
     ParticleApp(unsigned long ms_per_update, unsigned int window_size_x, unsigned int window_size_y,
                 Gedeng::String window_name)
-        : Application(ms_per_update, window_size_x, window_size_y, window_name), number_of_steps(10.0),
-          number_of_refinement_steps(10.0), bump_depth(0.1),
+        : Application(ms_per_update, window_size_x, window_size_y, window_name), particle_interval(0.1),
+          number_of_steps(10.0), number_of_refinement_steps(10.0), bump_depth(0.1),
           render_shader(Gedeng::Shader("Shader/bump.vs", "Shader/bump.fs")),
           camera(Gedeng::FPSCamera(90, 1920, 1080, 0.1, 1000.0)),
           albedo("Resources/Textures/PavingStones/PavingStones070_2K_Color.jpg", Gedeng::Texture::Settings()),
@@ -25,7 +26,7 @@ class ParticleApp : public Gedeng::Application {
         particles.set_color(glm::vec3(0.0f, 0.5f, 1.0f));
         particles.set_lifetime(1.0f, 1.5f);
         particles.set_size(0.1);
-        particles.set_interval(0.05f);
+        particles.set_interval(particle_interval);
         particles.set_number_of_particles(1);
         particles.set_texture(&albedo);
 
@@ -36,11 +37,15 @@ class ParticleApp : public Gedeng::Application {
     ~ParticleApp() = default;
 
     void fixed_update(double delta) override {
-        // camera.rotate(delta * 180, glm::vec3(0.0, 1.0, 0.0));
         camera.update(delta);
 
         if (Gedeng::Input::is_mouse_down(GLFW_MOUSE_BUTTON_LEFT))
             particles.set_position(camera.get_view_ray().get_plane_collision().collision_position);
+
+        if (Gedeng::Input::is_key_down(GLFW_KEY_2)) particle_interval = fmax(particle_interval + 0.1 * delta, 0.02);
+        if (Gedeng::Input::is_key_down(GLFW_KEY_1)) particle_interval = fmax(particle_interval - 0.1 * delta, 0.02);
+
+        particles.set_interval(particle_interval);
     }
 
     void dynamic_update(double delta) override {
@@ -76,6 +81,8 @@ class ParticleApp : public Gedeng::Application {
     }
 
   private:
+    float particle_interval;
+
     float number_of_steps;
     float number_of_refinement_steps;
     float bump_depth;