For assignment 4, I built a sketch which simulate the context of filling water into a tank.
Based on the example in class, I mainly played around with forces of resistance and buoyancy. At the very beginning, I was trying to create an effect that, if there is a force dragging balls to the bottom of water, balls will go back the water surface after the force is released. After I added the drag force, I felt like it was hard to visualize the force, so I further adjusted the sketch.
This time, instead of adding force on balls directly, I passed on the force to balls through water. By pressing the mouse, I changed the level of water, and thus adjust the position of balls. Later, to further simulate the situation, I drew a tap and add an object which represent the filling water. The final effect look like this: