2009

objects as emitters, use the Speed By Surface Operator on page 2886 operator
instead.
See also:
■ Speed By Icon Operator on page 2876
■ Keep Apart Operator on page 2894
Procedures
Example: To change particles' speed:
The Speed operator works on an instantaneous basis: It sets each particle's
speed once only, when it enters the event. Even if you animate the Speed
value, each particle moves at a constant rate of speed, defined by the value at
the time it enters the event. This procedure demonstrates a trick you can use
to change particle speed with an animated Speed value, thanks to Particle
Flow's looping ability.
1 Create a default particle system, and position it at the top of the
Perspective viewport.
2 Play the animation.
The particles fall downward at the default rate: 300 units per second.
3 Add a Send Out test at the bottom of Event 01.
4 Add a Speed operator to an empty area of the event display.
This creates a new event.
5
Turn on Auto Key, and move the time slider to frame 30.
6 In Particle View, click the new Speed 02 operator, and then in the Particle
View parameters panel, set Speed to 0.
This animates the Speed value from 300 at frame 0 to 0 at frame 30.
7
Turn off Auto Key.
8 Wire the Send Out test in Event 01 to Event 02.
9 Play the animation.
The particles born later move slower, but all still move at a constant rate
of speed.
2872 | Chapter 14 Space Warps and Particle Systems