9

Dynamics Utility 695
factor to the outside forces affecting each object
(gravit y, wind, and so on).
Thedefaultvalueof1resultsinnormalspeed.You
can scale down the simulation (make it slower) by
using values below 1 (from 0.1 to 1), and you can
scale up the simulation (make it faster) by using
values greater t han 1 (from 1 to 100). If you speed
up your simulation and objects begin to behave
incorrectly (going through objects, for example),
increase the Calc Intervals Per Frame value to
compensate.
Simulation Controls group
Relates to IK settings and the transfer of
momentum.
Use I K Joint Limi ts—Uses the current IK joint
limit settings as constraints for hie rarchies in the
simulation.
Use IK J oint Da mping—Uses the IK damping
settings as constraints for hierarchies in the
simulation.
Air Resistance group
Densit y per cent—Sets the air density in the
simulation. A setting of 100 is the air at sea level.
A setting of 0 is a total vacuum.
When a nything moves, it hits air resistance (except
in space). The faster it moves, the higher t he
relative air resistance with the square of the speed.
Thus, air resistance imposes an upper limit on the
speed of things that are falling with gravity, and
also makes objects tumble due to the effect of air
resistance on each face of the object.
Clo se—Closes the Dy namics utility.
D yn amics Proper ties Material Editor rollo ut
The three spinners in the Dynamics Properties
rollout in the Material Editor let you specify
surface properties that affect the animation of an
object upon collision with another object. If there
are no collisions in your simulation, these settings
have no effect.
Because the Dy namics Proper ties rollout is
available at the top level of any material (including
sub-materials), you c an specify different sur face
dynamic pro perties for each face in an object.
There are also controls in the Dynamics utility that
let you adjust the surface properties at the object
level, but only the Material Editor lets you alter the
surface properties at the sub-object level (through
use of a Multi/Sub-Object material).
As a default, the values in the Dynamics Properties
rollout provide a surface that’s similar to
Teflon-coated hardened steel. This is with values
of Bounce Coefficient equal to 1; with both Static
Frict ion and Dynamic Frict ion set to 0.
Bounce Coefficient—Determ ines how far an object
bounces after striking a surface (the higher the
value, the greater the bounce.) A value of 1
represents a bounce in which no kinetic energy
is lost.
Static Friction—Determines how difficult it is for an
object to start moving along a surface (the higher
this value, the more difficult the movement). If
somethingweighs10poundsandsitsonTeflon(a
sta tic friction of near zero), it takes almost no force
to make it move sideways. On the other hand, if it
sits on sandpaper, then the static friction might be
very high, around .5 to .8.