# World definition reference for the LowLevelPhysics2D API > Explore the properties you can use to configure a physics world in the Unity Editor. > **Note:** > > This documentation is about writing C# scripts using the `LowLevelPhysics2D` API. To use 2D physics in the Unity Editor using components like the Rigidbody 2D component, refer to [2D physics](/engine/6000.3/manual/unity2d/2d-physics.md.md) instead. Explore the properties you can use to configure a physics world in the Unity Editor, if you create a public `PhysicsWorldDefinition` object. For more information, refer to [Create a world with the LowLevelPhysics2D API](/engine/6000.3/manual/unity2d/2d-physics-api/create-objects/world.md). | **Property** | **Description** | | ---------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | **Gravity** | Sets the gravity Unity applies to all the bodies in the world. The default is -9.81 on the y-axis, which simulates Earth's gravity. | | **Simulation Type** | Sets when the physics simulation runs. The options are:**Fixed Update**: Runs the simulation automatically during the `FixedUpdate` event stage.**Update**: Runs the simulation automatically during the `Update` event stage.**Script**: The simulation runs only when you call [`PhysicsWorld.Simulate`](/engine/6000.3/script-reference/unityengine/lowlevelphysics2d/physicsworld/simulate.md).For more information, refer to [Event functions](/engine/6000.3/manual/scripting/object-oriented-development/managing-update-order/event-functions.md). | | **Simulation Sub Steps** | Sets the number of times the physics simulation runs per step to calculate stable values. If your world includes a complex set of joints, increasing this value can improve performance. The default is 4. | | **Simulation Workers** | Sets the number of threads the simulation uses. The default is 64. The number of threads might be limited by the number of available CPU cores on the device. | | **Transform Write Mode** | Sets the method Unity uses to copy the position of the physics body to the Transform component on the GameObject. The options are:**Off**: Doesn't copy the position or rotation.**Fast 2D**: Copies the position and one rotational axis, so any 3D rotations are ignored. This is the default.**Slow 3D**: Copies the position and the full 3D rotation.For more information, refer to [Move a GameObject](/engine/6000.3/manual/unity2d/2d-physics-api/create-objects/move-gameobject.md). | | **Transform Plane** | Determines which 3D space to convert the final 2D positions to. The options are:**XY**: The x-axis remains horizontal and the y-axis remains vertical, so that the world faces the camera in 3D space. This is the default.**XZ**: The x-axis remains horizontal but the y-axis becomes depth, so that the world lies flat in 3D space.**ZY**: The x-axis becomes depth but the y-axis remains vertical, so that the world stands upright in 3D space.For more information, refer to [Use 2D physics in 3D space using the LowLevelPhysics2D API](/engine/6000.3/manual/unity2d/2d-physics-api/3d-planes.md). | | **Transform Tweening** | Interpolates or extrapolates the position of the physics body between simulation updates, and writes the position to the Transform component. This property has no effect if you disable **Transform Write Mode**. For more information, refer to [Move a GameObject](/engine/6000.3/manual/unity2d/2d-physics-api/create-objects/move-gameobject.md). | | **Sleeping Allowed** | Removes bodies from physics calculations when they move at a slower speed than their **Sleep Threshold** value, to save processor time. When a sleeping body receives a collision or force, Unity wakes up the body and continues to include it in physics calculations. The recommended best practice is to leave this property enabled. | | **Continuous Allowed** | Enables continuous collision detection to prevent moving bodies tunnelling through static bodies. For more information, refer to [Configure collisions between LowLevelPhysics2D API objects](/engine/6000.3/manual/unity2d/2d-physics-api/interactions/collisions-enable.md). | | **Contact Filter Callbacks** | Enables physics objects optionally calling the `IContactFilterCallback` method of a shape if it makes contact with another shape, so you can run your own code that determines whether the shapes should collide. | | **Pre Solve Callbacks** | Enables physics objects optionally calling the `OnPreSolve2D` method of a dynamic body before Unity calculates the collision response, so you can run your own code. | | **Auto Body Update Callbacks** | Enables physics objects optionally calling the `IBodyUpdateCallback` method of a body if it's updated, so you can run your own code. | | **Auto Contact Callbacks** | Enables physics objects optionally calling the `OnContactBegin2D` and `OnContactEnd2D` methods of a shape if it makes contact with another shape, so you can run your own code. For more information, refer to [Detect collisions between LowLevelPhysics2D API objects](/engine/6000.3/manual/unity2d/2d-physics-api/interactions/collision-handle.md) | | **Auto Trigger Callbacks** | Enables physics objects optionally calling the `OnTriggerBegin2D` and `OnTriggerEnd2D` methods of a shape if it makes contact with another shape, so you can run your own code. For more information, refer to [Detect collisions between LowLevelPhysics2D API objects](/engine/6000.3/manual/unity2d/2d-physics-api/interactions/collision-handle.md). | | **Auto Joint Threshold Callbacks** | Enables physics objects optionally calling the `OnJointThreshold2D` method of a joint if it exceeds its **Force Threshold** or **Torque Threshold** value. | | **Bounce Threshold** | Sets the collision velocity in meters per second that causes objects to bounce. Avoid very small values, otherwise Unity can't put bodies to sleep to reduce CPU time. | | **Contact Hit Event Threshold** | Sets the relative speed in meters per second that two shapes must reach to generate a contact hit event. | | **Contact Frequency** | Sets the stiffness of how objects respond to contact in Hertz (cycles per second). A lower value makes contact softer and spongier. A higher value makes contact harder and more rigid. | | **Contact Damping** | Sets how quickly objects absorb the shock of a collision. A lower value makes objects less likely to settle after a collision. A higher value makes objects settle more quickly. The default value is 10. | | **Contact Speed** | Sets the speed Unity can push overlapping objects apart to separate them, in meters per second. The default value is 3. | | **Maximum Linear Speed** | Sets the maximum speed of objects in the world, in meters per second. | | **Draw Options** | Determines which bodies, shapes, joints, and collisions Unity draws. The options are:**Off****Selected Bodies**: Draws the bodies attached to GameObjects you select in the **Hierarchy** window.**Selected Shapes**: Draws the shapes attached to GameObjects you select in the **Hierarchy** window.**Selected Shape Bounds**: Draws the bounds of shapes attached to GameObjects you select in the **Hierarchy** window.**Selected Joints**: Draws the joints attached to GameObjects you select in the **Hierarchy** window.**All Bodies**: Draws all bodies.**All Shapes**: Draws all shapes.**All Shape Bounds**: Draws the bounds of all shapes.**All Joints**: Draws all joints.**All Contact Points**: Draws the points where shapes touch.**All Contact Normal**: Draws the direction that force is applied at contact points.**All Contact Impulse**: Draws the amount of force applied at contact points.**All Contact Friction**: Draws the friction forces at contact points.**All Solver Islands**: Draws groups of connected bodies and joints.**Default Selected**: Draws the physics objects attached to GameObjects you select in the **Hierarchy** window.**Default All**: Draws everything.For more information, refer to [Draw a debug visualization of objects](/engine/6000.3/manual/unity2d/2d-physics-api/create-objects/debug-drawing.md). | | **Draw Fill Options** | Defines which parts of shapes Unity draws. The options are:**Interior**: Draws the interior of the shape.**Outline**: Draws the outline of the shape.**Orientation**: Draws a line that represents the orientation of the shape. | | **Draw Thickness** | Sets the thickness of the lines Unity draws in pixels. | | **Draw Fill Alpha** | Sets the transparency of the color Unity uses to fill shapes. Accepted values range from 0 to 1. This property has no effect if you disable **Outline** in **Draw Fill Options**. | | **Draw Point Scale** | Sets the size of the points that Unity draws. | | **Draw Normal Scale** | Sets the size of the contact normals for joints that Unity draws. | | **Draw Impulse Scale** | Sets the size of the contact impulses for joints that Unity draws. | | **Draw Capacity** | Sets the initial number of objects Unity allocates memory to draw. If you set this to a higher value than the default of 0, Unity doesn't resize the buffer when it draws more elements, which prevents Unity allocating memory that needs garbage collection. | | **Draw Colors** | Sets the different colors Unity uses to draw each element. | ## Additional resources * [Create a world with the LowLevelPhysics2D API](/engine/6000.3/manual/unity2d/2d-physics-api/create-objects/world.md) * [Configure LowLevelPhysics2D API scenes with definitions](/engine/6000.3/manual/unity2d/2d-physics-api/properties/definitions.md) * [Configure global LowLevelPhysics2D API settings](/engine/6000.3/manual/unity2d/2d-physics-api/properties/global-settings.md)