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186 RIGID BODIES
DYNAMICS
DYNAMICS
RIGID BODIES 187
If you were to hold out a piece of paper and blow along its top edge, the airstream
would create lift — as the air passes over the paper, it lifts up the sheet until the
pressure is equal on both sides of the paper.
A practical example of lift.
Blow across a hanging piece of
paper and the airstream will
create a lifting force that will
move the paper into line with
the airstream.
Occasionally, paradoxical situations may arise such as motion that heads into the
wind. In such cases you should reduce the lift in one of two places. You can reduce
the parameter either in the Wind eld (Lift Coeff.) or the Rigid Body Dynamic dialog
(Lift). The latter is usually preferable since it enables you to adjust the lift for a
uncooperative object without affecting the ight of the other objects.
Impact
The Impact value determines the strength of the air force that will be exerted on
body surfaces that face the wind. The strength of the impact force is proportional
to the surface area facing the wind and the relative velocity of the body compared
to the wind.
Drag
When air streams over a body, small eddies will beat against the body’s surfaces,
causing deceleration. The Drag parameter denes the strength of this effect. This
decelerating effect is usually minor but occasionally it can have a telling inuence
on the object’s motion.
Linear, Angular
These settings work with the Linear Coeff. and Angular Coeff. settings for the Wind eld.
For details on these settings, look up “Linear Coeff., Angular Coeff.” in the index.