Computer animation physics or game physics are laws of physics as they are defined within a simulation or video game, and the programming logic used to implement these laws. Game physics vary greatly in their degree of similarity to real-world physics. Sometimes, the physics of a game may be designed to mimic the physics of the real world as accurately as is feasible, in order to appear realistic to the player or observer. In other cases, games may intentionally deviate from actual physics for gameplay purposes. Common examples in platform games include the ability to start moving horizontally or change direction in mid-air and the double jump ability found in some games. Setting the values of physical parameters, such as the amount of gravity present, is also a part of defining the game physics of a particular game. There are several elements that form components of simulation physics including the physics engine, program code that is used to simulate Newtonian physics within the environment, and collision detection, used to solve the problem of determining when any two or more physical objects in the environment cross each other's path. Physics simulations There are two central types of physics simulations: rigid body and soft-body simulators. In a rigid body simulation objects are grouped into categories based on how they should interact and are less performance intensive. Soft-body physics involves simulating individual sections of each object such that it behaves in a more realistic way. Particle systems A common aspect of computer games that model some type of conflict is the explosion. Early computer games used the simple expedient of repeating the same explosion in each circumstance. However, in the real world an explosion can vary depending on the terrain, altitude of the explosion, and the type of solid bodies being impacted. Depending on the processing power available, the effects of the explosion can be modeled as the split and shattered components propelled by the expanding gas. This is modelled by means of a particle system simulation. A particle system model allows a variety of other physical phenomena to be simulated, including smoke, moving water, precipitation, and so forth. The individual particles within the system are modelled using the other elements of the physics simulation rules, with the limitation that the number of particles that can be simulated is restricted by the computing power of the hardware. Thus explosions may need to be