Smooth collisions

(springy bounce) - Hey, welcome back. You probably noticed that the ping pong ball stimulator looks a little more like sand than water. For instance, the balls can pile up on each other like this. We used a stimulation much like this in Finding Dory. For instance, the sand in this shot. And the East Australian current in this shot. To create more water-like stimulation, we need to remove the hard boundary of the balls. They don't just bounce off like ping pong balls. They kind of smush together to create a soft collision. The smooth collisions are an approximation of the pressure forces that water normally experiences. There's a fancy name for this kind of stimulation. It's called "smoothed particle hydrodynamics" or "SPH" for short. Hydrodynamics literally means the motion of fluids. Now let's look at how lots of smooth particles interact. We can control how the particles collide using this parameter called Collision softness. Okay, so this is getting pretty close. Another parameter we can control is called Viscosity. Viscosity is a measure of how easily things flow. Fluids with low viscosity like water, flow pretty freely as we see here. Fluids with high viscosity like honey, flow more slowly. Like this. (water rippling) The more particles you add, the more computation is needed and the slower the program responds. (slow motion water ripple) Here's an example of SPH from Finding Nemo. It takes place inside the mouth of a whale. We've drawn the particles as balls here so you can watch their motion. In the next exercise, you'll get some practice experimenting with these different parameters to get a wide range of behaviors. See you soon!