How do you named the sketch?

With the same name it came with. "PHYSICS_02.pde".

Currently working on: http://namainstrument.tumblr.com/

If you are using toxiclibs-0021 then to run that code, you need to...

import toxi.physics3d.*;
import toxi.physics3d.behaviors.*;

...and then rename some stuff to 3D like VerletPhysics3D, VerletParticle3D, GravityBehavior3D

Nope, I'm using 0020. - I thought it might be this issue, and re-installed it. Same problem!