CoppeliaSim currently supports five different physics engines: the Bullet physics library, the Open Dynamics Engine, the MuJoCo physics engine, the Vortex Studio engine and the Newton Dynamics engine. There are smaller differences between the engines, but one can switch at any time from one to another, depending on one's needs. The reason for the large diversity in physics engine support in CoppeliaSim is that physics simulation is a complex task, that can be achieved by emphasising one or another aspect of a simulation, such as precision/realism, speed, or with support of diverse features:
[Open Dynamics Engine]
A physics engine allows simulating interactions between objects that are near to real-world object interactions. It allows objects to fall, collide, bounce back, but it also allows a manipulator to grasp objects, a conveyor belt to drive parts forward, or a vehicle to roll in a realistic fashion over uneven terrain. Following figures illustrates such a simulation:
Unlike many other simulation software packages, CoppeliaSim is not a pure physics engine centered simulator. It can rather be seen as a hybrid simulator, that combines kinematics and dynamics in order to obtain the best performance for various simulation scenarios. Nowadays, physics engines are still relying on many approximations and are relatively imprecise and slow, and wherever possible you should try to use kinematics instead (e.g. for robotic manipulators) and only rely on dynamics where otherwise not feasible (e.g. a robotic manipulator's gripper, mobile robots).