diff --git a/Cargo.lock b/Cargo.lock
index 8ba689a..dd1d7cf 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1,5 +1,39 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
+[[package]]
+name = "approx"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3f2a05fd1bd10b2527e20a2cd32d8873d115b8b39fe219ee25f42a8aca6ba278"
+dependencies = [
+ "num-traits",
+]
+
+[[package]]
+name = "autocfg"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cdb031dd78e28731d87d56cc8ffef4a8f36ca26c38fe2de700543e627f8a464a"
+
+[[package]]
+name = "num-traits"
+version = "0.2.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9a64b1ec5cda2586e284722486d802acf1f7dbdc623e2bfc57e65ca1cd099290"
+dependencies = [
+ "autocfg",
+]
+
+[[package]]
+name = "structs"
+version = "0.1.0"
+dependencies = [
+ "approx",
+]
+
 [[package]]
 name = "tuples"
 version = "0.1.0"
+dependencies = [
+ "structs",
+]
diff --git a/Cargo.toml b/Cargo.toml
index 016dc20..5a86c4f 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,3 +7,4 @@ edition = "2018"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+structs = { path = "structs" }
diff --git a/src/main.rs b/src/main.rs
index e7a11a9..b746f33 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,3 +1,71 @@
-fn main() {
-    println!("Hello, world!");
+use structs::Tuple;
+
+use std::fmt;
+
+#[derive(Debug)]
+struct Environment {
+    gravity: Tuple,
+    wind: Tuple,
+}
+
+#[derive(Debug, Clone, Copy)]
+struct Projectile {
+    position: Tuple,
+    velocity: Tuple,
+}
+
+impl Projectile {
+
+    fn new(position: Tuple, velocity: Tuple) -> Projectile {
+        if !position.is_point() {
+            panic!("position can not be a vector");
+        }
+
+        if !velocity.is_vector() {
+            panic!("velocity can not be point");
+        }
+
+        Projectile {
+            position: position,
+            velocity: velocity,
+        }
+    }
+}
+
+impl Projectile {
+    fn tick(&mut self, env: &Environment) {
+        self.position = self.position + self.velocity;
+        self.velocity = env.wind + env.gravity;
+    }
+}
+
+impl fmt::Display for Projectile {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "pos: {}, vel {}", self.position, self.velocity)
+    }
+}
+
+fn init_env() -> Environment {
+    Environment {
+            gravity: Tuple::vector(0.0, 0.0, -0.98),
+            wind: Tuple::vector(0.0, 0.0, 0.0),
+    }
+}
+
+fn main() {
+    let env = init_env();
+
+    let mut ball = Projectile::new(
+        Tuple::point(0.0, 0.0, 1.0),
+        Tuple::vector(1.0, 0.0, 0.0),
+    );
+
+    let mut tick = 0;
+    println!("tick {} the ball {}", tick, ball);
+    while ball.position.z() > 0.0 {
+        ball.tick(&env);
+
+        println!("tick {} the ball {}", tick, ball);
+        tick += 1;
+    }
 }