# Design: Physics & Puck Dynamics (M2)

## Goal
Implement basic physical properties for the puck to make movement feel natural: gradual slowing down (friction) and energy loss upon hitting boundaries (restitution).

## Architecture
The physics logic will be integrated into the `World.Update` loop. Constants for physical properties will be defined to allow easy tuning of the game feel.

## Implementation Details

### 1. Physical Constants
The following constants will be introduced:
- `PuckFriction`: Multiplier applied to velocity every frame (e.g., `0.99`).
- `PuckRestitution`: Multiplier applied to velocity upon boundary collision (e.g., `0.8`).
- `StopThreshold`: Minimum velocity magnitude below which the puck is forced to a complete stop (e.g., `0.1`).

### 2. Movement Logic (World.Update)
The update loop for the puck will follow these steps:
1. **Apply Friction**: `velocity = velocity * PuckFriction`.
2. **Stop Check**: If `length(velocity) < StopThreshold`, then `velocity = (0, 0)`.
3. **Position Update**: `position = position + velocity`.
4. **Boundary Collision**:
    - If the puck hits a boundary (considering its radius):
        - Invert the velocity component perpendicular to the boundary.
        - Multiply the resulting velocity by `PuckRestitution`.
        - **Correction**: Snap the puck's position to be exactly on the boundary edge to prevent it from getting stuck inside the wall.

## Success Criteria
- The puck gradually slows down and eventually stops.
- The puck loses speed after bouncing off the walls.
- The puck does not get stuck in the boundaries.