The user wants me to create a physics simulation with:
1. A heptagon (7-sided polygon) that rotates 360 degrees every 5 seconds
2. 20 numbered balls (1-20) that drop from the center
3. Gravity and friction
4. Ball-to-ball collisions
5. Ball-to-wall collisions with the rotating heptagon
6. Each ball shows its number rotating with the ball's spin

This is a complex physics simulation that I'll implement in a single HTML file using canvas for rendering and custom physics for collisions.

Let me plan the implementation:
1. Canvas setup
2. Heptagon that rotates at 360°/5s = 72°/second
3. Ball physics: position, velocity, angular velocity
4. Gravity: constant downward acceleration
5. Friction: damping on velocity
6. Ball-ball collision detection and response
7. Ball-wall collision with rotating heptagon walls
8. Render with ball rotation shown by number orientation

I'll implement all the math myself for collision detection.

I've created the index.html file with a physics simulation. Let me verify it exists and review it to make sure it meets all the requirements:

1. ✅ 20 numbered balls (1 to 20)
2. ✅ Balls drop from the center
3. ✅ Heptagon (7-sided polygon) that spins 360° every 5 seconds
4. ✅ Balls affected by gravity
5. ✅ Balls affected by friction
6. ✅ Ball-to-ball collision detection
7. ✅ Ball-to-wall collision with rotating heptagon
8. ✅ Each ball shows its spin via rotation of its number
9. ✅ All self-contained (CSS, JS in one file)
10. ✅ No external resources

The implementation includes:
- Custom physics engine with gravity and friction
- Ball-to-ball collision with impulse-based resolution
- Ball-to-wall collision with rotating walls (accounting for wall velocity at contact point)
- Visual rotation of ball numbers based on angular velocity
- Heptagon with glow effects

Let me verify the file was created properly.

The file has been created successfully. Let me confirm the implementation is correct by checking key parts.