Simplified models of physical behaviors are generally preferred if they are more efficient, easier to accelerate (through pre-computation, clever data structures, or SIMD/GPGPU), or satisfy desirable mathematical properties (such as unconditional stability or volume conservation when a soft body undergoes deformation).
Star Trek II: The Wrath of Khan famously used particle systems in the Genesis explosion scene to create the visual effect of a flaming shockwave engulfing a planet.
Valve later developed Half-Life and used rigid body physics to create environmental puzzles for the player, such as obstacles that could not be reached without stacking boxes.
Speed is therefore not strictly a necessity in the production of special effects but is still desirable for reasonably responsive feedback and because the hardware required for slower methods is more expensive.
The physical accuracy of small details in a special effect are not meaningful to their visual appeal, restrict the amount of control that artists and directors can exert over behavior, and increase the monetary cost and time required to achieve results.
Simplified rigid body physics is relatively cheap and easy to implement, which is why it appeared in interactive games and simulations earlier than most other techniques.
[3][4] Unconditional stability and ease of configuration are particularly desirable properties of soft body simulations that can be difficult to achieve with spring-mesh systems, although they are still often used in games because of their simplicity and speed.
For relatively free bodies of liquid, Lagrangian or semi-Lagrangian methods are often used to speed up the simulation by treating particles as finite elements of fluid (or carriers of physical properties) and approximating the Navier-Stokes equations .
[8] Particle systems are an extremely popular technique for creating visual effects in movies and games because of their ease of implementation, efficiency, extensibility, and artist control.
In physically based animation, flocking refers to a technique that models the complex behavior of birds, schools of fish, and swarms of insects using virtual forces.
In these simulations, individual members of the flock (sometimes called boids, short for bird-oid) act without collaboration using only information about the position and velocity of their peers to create the illusion of synchronized, group behavior efficiently.
Visually, these static methods cannot easily convey complex interactions with the environment and make lifelike character motion difficult to accomplish.
[11] The adoption of physically based character animation, as opposed to more static methods, has been slow in the gaming industry due to the increased cost and complexity associated with its use.