3D Physics for object-oriented projects

This section describes the main components available through Unity’s built-in 3D physics engineA system that simulates aspects of physical systems so that objects can accelerate correctly and be affected by collisions, gravity and other forces. More info
See in Glossary, which you can use in object-oriented projects. It includes the following:

• An overview of the main physics-related concepts: RigidbodiesA component that allows a GameObject to be affected by simulated gravity and other forces. More info
  See in Glossary, CollidersAn invisible shape that is used to handle physical collisions for an object. A collider doesn’t need to be exactly the same shape as the object’s mesh - a rough approximation is often more efficient and indistinguishable in gameplay. More info
  See in Glossary, JointsA physics component allowing a dynamic connection between rigidbodies, usually allowing some degree of movement such as a hinge. More info
  See in Glossary, physics articulations and Character ControllersA simple, capsule-shaped collider component with specialized features for behaving as a character in a game. Unlike true collider components, a rigidbody is not needed and the momentum effects are not realistic. More info
  See in Glossary.
• Some explanations on specific physics contexts: Continuous collision detectionA collision detection method that calculates and resolves collisions over the entire physics simulation step. This can prevent fast-moving objects from tunnelling through walls during a simulation step. More info
  See in Glossary and Multi-scene physics.
• A description of the Physics Debug Visualization.

In addition, the 3D Physics Reference provides a detailed description of all available components and the Physics HOWTOs section contains a few tips about common physics-related tasks.