Engines that use bounding boxes or bounding spheres as the final shape for collision detection are considered extremely simple. This may be a bounding box, sphere, or convex hull. The simplified mesh used for physics processing is often referred to as the collision geometry. It would thus be impossible to insert a rod or fire a projectile through the handle holes on the vase, because the physics engine model is based on the cylinder and is unaware of the handles. For purpose of speed, a second, simplified invisible mesh is used to represent the object to the physics engine so that the physics engine treats the example vase as a simple cylinder. One of these meshes is the highly complex and detailed shape visible to the player in the game, such as a vase with elegant curved and looping handles. Typically, most 3D objects in games are represented by two separate meshes or shapes. Objects in games interact with the player, the environment, and each other.
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Some form of limited fluid dynamics simulation is sometimes provided to simulate water and other liquids as well as the flow of fire and explosions through the air. Soft body physics are also used for particle effects, liquids and cloth. Physically-based character animation in the past only used rigid body dynamics because they are faster and easier to calculate, but modern games and movies are starting to use soft body physics. This requires more accurate physics so that, for example, the momentum of an object can knock over an obstacle or lift a sinking object. However some game engines, such as Source, use physics in puzzles or in combat situations. More often than not, the simulation is geared towards providing a "perceptually correct" approximation rather than a real simulation. This leads to designs for physics engines that produce results in real-time but that replicate real world physics only for simple cases and typically with some approximation. In most computer games, speed of the processors and gameplay are more important than accuracy of simulation. Main articles: Game engine and Game physics Tire manufacturers use physics simulations to examine how new tire tread types will perform under wet and dry conditions, using new tire materials of varying flexibility and under different levels of weight loading. As with many calculation-laden processes in computing, the accuracy of the simulation is related to the resolution of the simulation and the precision of the calculations small fluctuations not modeled in the simulation can drastically change the predicted results. The techniques can be used to model weather patterns in weather forecasting, wind tunnel data for designing air- and watercraft or motor vehicles including racecars, and thermal cooling of computer processors for improving heat sinks. Due to the requirements of speed and high precision, special computer processors known as vector processors were developed to accelerate the calculations. Physics engines have been commonly used on supercomputers since the 1980s to perform computational fluid dynamics modeling, where particles are assigned force vectors that are combined to show circulation.
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The results were calculated a single time only, and were tabulated into printed tables handed out to the artillery commanders. It was used to design ballistics tables to help the United States military estimate where artillery shells of various mass would land when fired at varying angles and gunpowder charges, also accounting for drift caused by wind. One of the first general purpose computers, ENIAC, was used as a very simple type of physics engine.