Legacy Documentation: Version 2018.2 (Go to current version)
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Physics 2D Settings
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Physics Manager

Use the Physics Manager to apply global settings for 3D physics. To access it, go to Edit > Project SettingsA broad collection of settings which allow you to configure how Physics, Audio, Networking, Graphics, Input and many other areas of your Project behave. More info
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> Physics. To manage global settings for 2D physics, use the Physics 2D Manager.

The settings of the PhysicsManager define limits on the accuracy of the physical simulation. Generally speaking, a more accurate simulation requires more processing overhead, so these settings offer a way to trade off accuracy against performance. See the Physics section of the manual for further information.

The PhysicsManager, shown in the Inspector window.
The PhysicsManager, shown in the Inspector window.
Property: Function:
Gravity Use the x, y and z axes to set the amount of gravity applied to all Rigidbody components. For realistic gravity settings, apply a negative number to the y axis. Gravity is defined in world units per seconds squared.
Note: If you increase the gravity, you might need to also increase the Default Solver Iterations value to maintain stable contacts.
Default Material Use this field to define the default Physics Material that is used if none has been assigned to an individual ColliderAn 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
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Bounce Threshold Use this to set a velocity value. If two colliding objects have a relative velocity below this value, they do not bounce off each other. This value also reduces jitter, so it is not recommended to set it to a very low value.
Sleep Threshold Use this to set a global energy threshold, below which a non-kinematic RigidbodyA component that allows a GameObject to be affected by simulated gravity and other forces. More info
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(that is, one that is not controlled by the physics system) may go to sleep. When a Rigidbody is sleeping, it is not updated every frame, making it less resource-intensive. If a Rigidbody’s kinetic energy divided by its mass is below this threshold, it is a candidate for sleeping.
Default Contact Offset Use this to set the distance the collision detectionAn automatic process performed by Unity which determines whether a moving GameObject with a rigidbody and collider component has come into contact with any other colliders. More info
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system uses to generate collisionA collision occurs when the physics engine detects that the colliders of two GameObjects make contact or overlap, when at least one has a rigidbody component and is in motion. More info
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contacts. The value must be positive, and if set too close to zero, it can cause jitter. This is set to 0.01 by default. Colliders only generate collision contacts if their distance is less than the sum of their contact offset values.
Default Solver Iterations Solvers are small 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
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tasks which determine a number of physics interactions, such as the movements of jointsA physics component allowing a dynamic connection between rigidbodies, usually allowing some degree of movement such as a hinge. More info
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or managing contact between overlapping Rigidbody components. Use Default Solver Iterations to define how many solver processes Unity runs on every physics frame. This affects the quality of the solver output and it’s advisable to change the property in case non-default Time.fixedDeltaTime is used, or the configuration is extra demanding. Typically, it’s used to reduce the jitter resulting from joints or contacts.
Default Solver Velocity Iterations Use this to set how many velocity processes a solver performs in each physics frame. The more processes the solver performs, the higher the accuracy of the resulting exit velocity after a Rigidbody bounce. If you experience problems with jointed Rigidbody components or Ragdolls moving too much after collisions, try increasing this value.
Queries Hit Backfaces Tick the checkbox if you want physics queries (such as Physics.Raycast) to detect hits with the backface triangles of MeshColliders. This setting is unticked by default.
Queries Hit Triggers Tick the checkbox if you want physics hit tests (such as Raycasts, SphereCasts and SphereTests) to return a hit when they intersect with a Collider marked as a Trigger. Individual raycasts can override this behavior. This setting is ticked by default.
Enable Adaptive Force The adaptive force affects the way forces are transmitted through a pile or stack of objects, to give more realistic behaviour. Tick this box to enable the adaptive force. This setting is unticked by default.
Contacts Generation Choose a contact generation method:

Persistent Contacts Manifold (PCM): Regenerates fewer contacts every physics frame and shares more contact data across frames. The PCM contacts generation path is also more accurate, and usually produces better collision feedback in most of the cases. See Nvidia documentation on Persistent Contact Manifold for more information.
Legacy Contacts Generation: Generates contacts using the separating axis theorem (see dyn4j.org’s guide to SAT).

PCM is more efficient, but for projects made in versions of Unity earlier than Unity 5.5, you might find it easier to continue using SAT, to avoid needing to retweak physics slightly. PCM can result in a slightly different bounce, and fewer useless contacts end up in the contacts buffers (that is, the arrays you get in the Collision instance passed to OnCollisionEnter, OnCollisionStay, and OnCollisionExit).
Auto Simulation Run the physics simulation automatically or allow explicit control over it
Auto Sync Transforms Automatically sync transform changes with the physics system whenever a Transform componentA Transform component determines the Position, Rotation, and Scale of each object in the scene. Every GameObject has a Transform. More info
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Contact Pairs Mode Select the type of contact pair generation to use:

Default Contact Pairs: Receive collision and trigger events from all contact pairs except kinematic-kinematic and kinematic-static pairs.
Enable Kinematic Kinematic Pairs: Receive collision and trigger events from kinematic-kinematic contact pairs.
Enable Kinematic Static Pairs: Receive collision and trigger events from kinematic-static contact pairs.
Enable All Contact Pairs:Receive collision and trigger events from all contact pairs.
Broadphase Type Choose which broad-phase algorithm to use in the physics simulation: Sweep and Prune Broadphase or Multibox Pruning Broadphase. Multi-box pruning uses a grid, and each grid cell performs sweep-and-prune. This usually helps improve performance if, for example, there are many GameObjectsThe fundamental object in Unity scenes, which can represent characters, props, scenery, cameras, waypoints, and more. A GameObject’s functionality is defined by the Components attached to it. More info
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in a flat world. For more information, see NVIDIA’s documentation on PhysX SDK and Rigid Body Collision.
World Bounds Define the 2D grid that encloses the world to prevent far away objects from affecting each other when using the Multibox Pruning Broadphase algorithm. This option is only available when you set Broadphase Type to Multibox Pruning Broadphase.
World Subdivisions The number of cells along the x and z axis in the 2D gri__ algorithm. This option is only available when you set Broadphase Type to Multibox Pruning Broadphase.
Layer Collision Matrix Use this to define how the layer-based collision detection system behaves.
Cloth Inter-Collision Control cloth particle Distance and Stiffness when setting up particles for Cloth intercollision.

  • 2018–08–10 Page amended with limited editorial review

  • Settings added in 5.5: Default Solver Iterations, Default Solver Velocity Iterations, Queries Hit Backfaces, Enable PCM

  • Physics Manager settings documentation updated in 2017.4

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Physics 2D Settings