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Using Forces in the ICE Tree

Forces make things move.

In the ICE tree, forces make particles and simulated deformed objects move according to different types of forces that imitate nature. Each particle cloud or simulated object can have multiple forces applied to it.

Physics in the ICE Tree

Although anything is possible in the world of 3D, Softimage needs to use physics based on the real world in order to calculate forces properly. As a result, the forces that are used in the ICE Tree are based on Newtonian physics.

You can, of course, bend the laws of physics to your own animation needs, which are not always restricted to the real world. Cartoons often break most conventional physics to achieve their effects. You can create your own force or simulation compounds using the nodes found within ICE.

Meanwhile, here are some of the main concepts that forces in the ICE Tree use:

• Velocity: the speed and direction of an object, or its rate of change in position. This is a vector.

• Speed: the amplitude of the velocity (the length of the velocity vector) but without the direction that velocity has. This is the ratio of the distance an object moves versus the time it takes.

• Acceleration: the rate of change of velocity.

For more information on velocity, speed, and acceleration, see ICE Particle Speed.

• Force: a push on an object that infers a change in velocity. It is also a vector that indicates the direction of the push. Its length determines the strength of the push.

Force is a vector that gets applied to an object to change its velocity, and the object’s mass is taken into consideration (Force = Mass * Acceleration). The Force is calculated by the change in velocity multiplied by the mass.

When the Simulate Particles node applies force to a particle’s position, it takes into account the particle mass.

• Mass: the quantity of matter of an object. The mass determines how quickly objects react to the forces applied to them and how they react in a collision with an obstacle. Objects with a higher mass tend to keep their velocity when exerting forces on them. Therefore, to make a change in an object’s motion, you need to apply stronger forces to an object with more mass than to one with little mass.

For more information, see ICE Particle Mass.

• Gravity: the attraction between all objects that have mass. Earth’s gravity is a downward acceleration exerted on objects.

For more information, see Gravity.

• Drag: a force applied by a fluid on a solid object in the opposite direction to its velocity. The force depends on the velocity of the object and its size, and on the density of the fluid.

For more information, see Drag Force.

Getting Forces into the ICE Tree

To use forces in the ICE tree, you can access forces from within the ICE tree or from any toolbar in Softimage. Each represents a different set of forces, but you can use both sets in the ICE tree.

You can get forces from:

• The ICE tree view’s preset manager — click the Task tab, select Particles from the drop-down list, and select the Forces group to see all available ICE force compounds. See Types of ICE Forces for information.

or

• The Get > Forces menu on the Simulate toolbar or the Get > Primitive > Control Object menu on any other toolbar. These are the simulation forces that have been available for previous versions of Softimage — see Types of Forces [ Forces for Simulations ].

You may want to work with these forces if you’re used to them, or also because each force is represented in the scene by its own control object. The control object lets you select, transform, rotate, and scale the force.

Force Attributes

There are several attributes that are used to define forces are used in a simulation. These attributes are used in several compounds, but you can also use them on their own in an ICE tree.

You can use any of these attributes by specifying them in the Get Data and Set Data nodes, as described in Using ICE Particle Attributes.

For more information on attributes in general and a list of all available ICE attributes, see ICE Attributes.

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