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move along the XY plane, and when they're closer to the vertical sides,
they move downward. If you want them to move upward instead, set
Speed to a negative value.
Next, you'll discover how the Control Speed Continuously option alters
particle behavior.
11 In the Speed By Surface parameters, choose Control Speed Continuously,
and then drag the time slider.
The particles spread out from the emitter, and then start orbiting the
cylinder in a roughly cylindrical overall formation. The software
continually checks to see which side of the cylinder a particle is closest
to, and, if necessary, changes its direction to make it travel parallel to
that side. You can affect the size of the particles' orbits by changing their
speed.
Lastly, you'll see how to contain particle motion within the cylinder.
12 Make the cylinder considerably larger: Radius=60 and Height=90. Activate
the Perspective viewport, if necessary, and then press F3 to set it to
Wireframe view.
13 In Particle View, click the Speed 01 operator and set Direction to Random
3D.
14 Click the Speed By Surface operator. Set Speed to 300 if necessary. In the
Direction group, choose Out Of Surface, and then drag the time slider.
After exiting the emitter, the particles always move away from the nearest
surface, with the result that they end up milling about in the center of
the cylinder.
15 Gradually increase the Speed value, up to 1,000 or so.
The particles start to spread out vertically, and eventually start moving
so fast that they escape the cylinder. You can make them stay inside the
cylinder by letting them accelerate more quickly, so they can turn before
moving past the nearest surface.
16 Increase the Accel Limit setting until the particles no longer exit the
cylinder.
17 Try giving the particles more room to move about in by increasing the
size of the emitter. Also try changing other settings throughout the particle
system to see their effects. The possibilities don't end here, and the more
you experiment, the more you'll learn about how this powerful operator
works.
2888 | Chapter 14 Space Warps and Particle Systems