add some comments

cmd/root.go

@@ -45,6 +45,7 @@ func init() {
 	rootCmd.AddCommand(fireworksCmd)
 }
 
+// Execute starts the confetty command-line interface
 func Execute() {
 	if err := rootCmd.Execute(); err != nil {
 		fmt.Fprintln(os.Stderr, err)

physics/physics.go

@@ -4,32 +4,46 @@ import (
 	"math"
 )
 
+// Position is the location of an object on a 2-dimensional plane
 type Position Point
+
+// Velocity is the velocity vector of an object's motion
 type Velocity Vector
+
+// Acceleration is the acceleration vector of an object's motion
 type Acceleration Vector
 
+// Gravity is the acceleration of gravity
+// Downward (+) by g m/s²
 var Gravity = Acceleration{
 	X: 0,
 	Y: 9.81,
 }
 
+// Motion represents an objects motion
+// it keeps track of the position, velocity, and acceleration
 type Motion struct {
 	pos Position
 	vel Velocity
 	acc Acceleration
 }
 
+// Physics tracks the current motion and initial motion of an object along with
+// fps to account for the Update in frames rather than per second
 type Physics struct {
 	current Motion
 	initial Motion
 	fps     float64
 }
 
+// Vector represents a magnitude and a direction in the form of a Point
+// from the origin (0, 0)
 type Vector struct {
 	X float64
 	Y float64
 }
 
+// Point is a coordinate on a 2-dimensional plane
 type Point struct {
 	X float64
 	Y float64
@@ -40,6 +54,7 @@ func (a Point) Distance(b Point) float64 {
 	return math.Sqrt(math.Pow(b.X-a.X, 2) + math.Pow(b.Y-a.Y, 2))
 }
 
+// New initialize a physics simulation with simple motion
 func New(pos Point, vel, acc Vector, fps float64) *Physics {
 	motion := Motion{
 		pos: Position(pos),
@@ -53,10 +68,13 @@ func New(pos Point, vel, acc Vector, fps float64) *Physics {
 	}
 }
 
+// Reset resets the current motion back to the initial
 func (p *Physics) Reset() {
 	p.current = p.initial
 }
 
+// Update increases the position of the motion by the velocity
+// and increases the velocity by the acceleration
 func (p *Physics) Update() {
 	p.current.pos.X += p.current.vel.X / p.fps
 	p.current.pos.Y += p.current.vel.Y / p.fps
@@ -65,14 +83,19 @@ func (p *Physics) Update() {
 	p.current.vel.Y += p.current.acc.Y / p.fps
 }
 
+// Displacement calculates the displacement between the current position and
+// its initial position
 func (p Physics) Displacement() float64 {
 	return Point(p.initial.pos).Distance(Point(p.current.pos))
 }
 
+// PosX returns the integer value of the current x coordinate for motion
+// not to be confused with Posix :D
 func (p Physics) PosX() int {
 	return int(math.Round(p.current.pos.X))
 }
 
+// PosY returns the integer value of the current y coordinate for motion
 func (p Physics) PosY() int {
 	return int(math.Round(p.current.pos.Y))
 }