##### Physics Tab

The 'Phys' tab includes controls for physical object properties which are used in simulations.

###### General Properties

Mass: The mass of an object (in kilograms). The default mass is 1 kg. A level object's default mass is the sum of the mass of sub objects. Any other mass can be defined here.

Clear Mass: Clears a custom mass definition so that the default mass computation will be used.

Electric Charge: The amount of electric charge (coulomb). Can be positive or negative.

Surface Friction: A surface friction coefficient 0..1.

Rebound Energy: Describes how well the object keeps its kinetic energy in collisions. The value range is 0 .. 1. If the value is 1, the object keeps its kinetic energy and just changes the direction of its motion in a collision.

Elasticity: Objects ability to maintain its shape in a deforming situation such as a collision. If elasticity is zero, there is no force that restores the shape after a deformation. Rigidity: Describes how rigid the object shape is. The lower the value, the more freely object matter can react to forces and the less internal friction resisting the shape deformations exists. If the rigidity is zero, object geometry points act independently in simulations (elasticity defines a string force that maintains the shape).

Inertia: Describes how the mass is distributed in object volume. If the mass is concentrated in the middle of the object, the inertia is small and the object has a tendency to spin easily in collisions. If the mass is concentrated at outermost edges (say a hollow lead sphere), the object has a large resisting momentum and does not spin easily. The program computes a default estimate from the object mass and bounding box dimensions. Be careful when changing the default momentum; entering a value that is physically impossible will invalidate the collision impact calculations.

Clear Inertia: Removes a non default inertia definition. The value estimated by the program will be used.

Center of Gravity: The program estimates the center of gravity as an average of the surface geometry, but you can change it here if necessary.

Clear COG: Removes a non default COG definition. The value estimated by the program will be used.

Velocity: Defines the direction and speed of object's motion.

Spin: Defines how the object rotates around its object space axes. The unit is the selected angle unit per second. For example, (0, 180, 360) degrees per second.

###### Impact Properties

The impact system maintains an object attribute Impact Level, which can be used for key driven animations launched by collisions. For example, you can key frame a collision behavior and bind it to the Impact Level attribute.

Impact Duration: The duration of impact wave (measured in the selected time units - frames, seconds etc.). The impact wave runs linearly from zero to Amplitude during the duration time.

Amplitude: The maximal value of the Impact Level attribute during the impact wave processing.

Impact Level: The current value of Impact Level. You can use this control to test a choreography driven by the Impact Level attribute.

###### Fluid Dynamics Properties

Density: Describes how dense a matter where simulation happens is. A typical value range is 1..10. The denser the matter, the more it resists motions (or creates them in case the matter has a moving flow such as wind). This property is attached to objects that define a fluid such as the fan object.

Fluid Velocity: The speed of fluid flow as meters per second (the flow direction is defined by the fluid creator geometry, for example a fan axis). Also this property is attached to objects that define a fluid flow such as the fan object.

Fluid Pressure: The pressure of fluid. This value affects e.g. forces generated by a non symmetric fluid flow.

Fluid Friction: Object's friction coefficients in object space directions. Many objects are strongly non symmetric in this respect: for example, an airplane is designed to have a small friction in its natural peak-tail direction, but it has quite a strong friction against the wing planes. This property controls objects moving in fluid, not the fluid creator.

Fluid Symmetricity: Fluid flow symmetry with respect to object space axes. The value zero means symmetric flow. Non symmetric flows generate a pressure difference at the opposite sides and hence a force along the axis in question (for example: an airplane wing).