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718 Chapter 13: reactor
Inter face
Physical Properties
Mass—Arigidbody’smassgovernshowtheobject
interactswithotherobjects. Whenitsmassis
set to 0.0 (the default value), the object remains
fixed in spa ce during the simulation, although
other objects will be able to collide with it. For
example, you could use a fixed rigid body to create
a slope for other objects to roll down. Other values
allow the object to move during the simulat ion,
depending on other circumstances. A valid value
forMassisgreaterthanorequalto0.0.
Fr iction —Thecoefficientoffrictionfortheobject’s
surface. This affects how smoothly the rigid body
movesrelativetosurfacesit’sincontactwith.
The friction values for both objects combine
to produce a coefficient for the interaction. To
achieve realistic results, use va lues b etween 0.0 and
1.0. However, values up to 5.0 are accepted.
Elasticity—Thisvaluegovernstheeffectcollisions
have on the velocities of the rigid b ody ; in other
words, how "b ouncy" t he object is. Like Friction,
this is a pair-wise coefficient: When two objects
collide, their elasticity values combine to produce
a coefficient for the interaction. To achieve realistic
results, use values between 0.0 and 1.0. However,
values up to 5.0 are accepted.
Inactive—When on, the rigid body starts the
simulation in an inactive state. This means it
requires interaction with another object or system,
or the mouse, before it becomes active in the
simulation. For example, if you place an object
in midair, give it a mass and set it to Inactive,
when the simulation starts it sits in midair until
something interacts with it. Inac tive objects
require less computation during simulation.
Disable All Collisions—When on, the object doesn’t
collide with other objects in the scene; it simply
passes through them.
Unyielding—When on, the r igid b ody takes its
motion from the animation it already has in
3ds Max, rather than the physical simulation.
Other objects in the simulation can collide with it
and react to its motion, but its motion is governed
solelybythecurrentanimationin3dsMax,and
reactor will not create keyframes for it.
Phantom—A phantom object has no physical
presence in the simulation. Like an object with
Disable All Collisions on, it simply passes through
other objects. Un like an object with disabled
collisions, however, a phantom main tains collision
information about any objec ts that it passes
through during the simulation. You can then use
this collision information, for instance, to trigger
sounds or other effects. You can find out how to
access collision data in the Storing and Accessing
Collisions (page 2–774).
Shell—The radius of an extra "shell" around convex
shapes,whichreactorusesastheshape’ssurface
for collision-detection purposes. The simulation
tries to ensure that the distance between this shell
andotherobjectsisalwaysmorethanzero;in
other words, that the distance between the original