2009

2 Add a Cylinder primitive to the scene. Position it above the source icon:
X/Y=0 and Z=30. Set Radius=20 and Height=40.
3 Play the animation, and then stop.
The particles move downward, using the default starting setup.
4 Open Particle View and add a Speed By Surface operator to the end of
Event 01. Click the operator in the event to display its parameters panel
in Particle View.
5 In the Surface Geometry group, click Add, and then select the cylinder.
6 Play the animation again, and then stop.
The particles still move downward.
7 Go to frame 15, so you can see the particles, and then slowly move the
cylinder downward along the Z axis, while watching the particles in the
Perspective and Front viewports. Stop when the emitter is above the
cylinder.
As the bottom of the cylinder passes below the emitter, more and more
particles start moving on the XY plane rather than perpendicular to it.
That's because they eventually become closer to one of the vertical sides
of the cylinder, rather than the bottom, at which point they move
perpendicular to the vertical sides. When the top becomes the closest
side, the particles again move vertically, but upward instead of downward.
8 Move the cylinder back up until the emitter is at its vertical center. Then,
on the Modify panel, click the lower part of the Sides spinner to decrease
the number of sides, one at a time.
Each time you click, the particle streams traveling outward change, to
move perpendicular to the vertical sides as they change position. You
might also try rotating the cylinder, and note that the particle streams
also rotate, like the spokes of a wheel.
9 In the Speed By Surface parameters, change Direction to Out Of Surface,
and then move the cylinder up and down.
The overall behavior doesn't change much. Out Of Surface becomes more
useful when you use the Control Speed Continuously option, as you'll
observe shortly.
10 In the Speed By Surface parameters, change Direction to Parallel To
Surface, and then move the cylinder up and down.
Now the particle behavior is effectively opposite of that with the other
two options. When the particles are closer to the top or bottom, they
Particle Flow | 2887