diff --git a/src/main.rs b/src/main.rs
index 7958cb8..0cb98c3 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -28,6 +28,10 @@ fn fill_particles(app: &App, particles: &mut Vec<Particle>) {
 }
 
 fn model(app: &App) -> Model {
+    // One thing that tripped me up when begginning nannou was realizing
+    // that view and event methods are per window, and update functions are
+    // per app
+
     // Create a new window! Store the ID so we can refer to it later.
     let _window = app
         .new_window()
@@ -61,7 +65,12 @@ fn event(app: &App, model: &mut Model, event: WindowEvent) {
 }
 
 // Update the state of your application here. By default, this gets called right before `view`.
-fn update(_app: &App, _model: &mut Model, _update: Update) {}
+fn update(_app: &App, _model: &mut Model, _update: Update) {
+    _model.particles.iter_mut().for_each(|particle| {
+        let offset = (_app.time + particle.time_offset).sin() * 100.0;
+        particle.pos.x = particle.start_pos.x + offset
+    });
+}
 
 // Draw the state of your `Model` into the given `Frame` here.
 fn view(app: &App, model: &Model, frame: Frame) {
diff --git a/src/particle.rs b/src/particle.rs
index f34d181..9dd208e 100644
--- a/src/particle.rs
+++ b/src/particle.rs
@@ -4,15 +4,18 @@ use crate::PARTICLE_SIZE;
 use nannou::prelude::*;
 
 #[derive(Debug)]
-pub(crate) struct Particle {
-    pos: Vec2,
-    radius: f32,
+pub struct Particle {
+    pub pos: Vec2,
+    pub start_pos: Vec2,
+    pub radius: f32,
+    pub time_offset: f32,
 }
 
 impl Particle {
-    pub(crate) fn new(pos: Vec2) -> Self {
+    pub fn new(pos: Vec2) -> Self {
         Self {
             pos,
+            start_pos: pos,
             ..Default::default()
         }
     }
@@ -23,6 +26,8 @@ impl Default for Particle {
         Self {
             pos: Default::default(),
             radius: PARTICLE_SIZE,
+            start_pos: Default::default(),
+            time_offset: random_range(-PI, PI),
         }
     }
 }