1. Implement the basic graphics framework to draw N balls on the screen, and maintain the position/velocity state of each spherical object.
   
2. Making the particles move: Implement a symplectic Euler integrator which (as discussed in class) updates the particle velocity using applied forces, then updates the particle position. You can use random initial velocities (of a suitably bounded magnitude) to get started. Include a downward gravitational force.
3. Wall-particle collision detection and response (or "staying inside the box"): The particles are currently not constrained to stay inside the computational cell. Implement a scheme to detect collisions with the four walls, and modify the velocity to provide simple collision response, using a (particle-specific) restitution coefficient to attenuate normal velocity. Be careful how you update your particle velocity/position or you might find your particles sinking into the floor.
4. Adding sound: Everytime a ball hits a wall, you should play a suitable "click" sound to indicate that an impact was made, with amplitude proportional to the collision impulse magnitude.  Next, to avoid all collisions during a time-step producing "clicks" at the same time-step-size dependent instant, you can estimate the time of ball-wall collision more accurately, and shift the "click" sound in the sound buffer.  As an implementation detail, you can use a circular sound buffer to additively composite sounds into, then regularly xetract the next output sound clip (of suitable "buffer size"). See the documentation on how to stream sounds from a real-time application. Your sound should play clearly and without noticeable audio artifacts.
   
5. Make it interactive: You can pull particles around by applying forces to particles near your mouse position. You can also change, e.g., rotate, the direction of gravity using keyboard controls to make all the particles move.