Create an object with the Physics Core 2D API

Note: This documentation is about writing C# scripts using the Unity.U2D.Physics API. To use 2D physics in the Unity Editor using components like the Rigidbody 2D component, refer to 2D physics instead.

After you create a physics world, you can add physics objects to the world.

An object is usually made up of two parts:

A physics body, which defines the position, rotation, and velocity of the object. It doesn’t define an area.
One or more physics shapes attached to the body, which define the area that interacts with other shapes. Unity also automatically draws the shapes as a debug visualization.

You can add any number of shapes to a physics body. You can create shapes with the following geometries:

Circle
Capsule
Polygon
SegmentSegments are subsets of your player base, split apart by key differentiators. Viewing metrics and events by segment can reveal differences in-game behavior between different groups. More info
See in Glossary, which creates a line
Chain segment, which you use to create a series of connected line segments

Create a physics body and physics shape

Follow these steps:

Create objects that hold the properties of the body and shapes. Make them public fields so they display their properties in the Inspector window. For example:
```
public PhysicsBodyDefinition bodyDefinition = new PhysicsBodyDefinition();
public PhysicsShapeDefinition shapeDefinition = new PhysicsShapeDefinition();
```
A new definition has a set of default values. For more information about definitions and changing the default values, refer to Configure 2D physics properties using a definition.

You can also use PhysicsBody.defaultDefinition to get a definition object with the default values.
Use the CreateBody method of the world object to add a body to the world, and pass in the body definition.
```
PhysicsBody myObject = world.CreateBody(bodyDefinition);
```
Create a shape using a geometry object, for example a CircleGeometry object. For example, the following creates a circle with a radius of 2 meters.
```
CircleGeometry circleShape = new CircleGeometry { radius = 2f };
```
Attach the shape to the body using the CreateShape method of the body, and pass in the shape definition.
```
myObject.CreateShape(circleShape, shapeDefinition);
```
If your script is in a MonoBehaviour class attached to a GameObject, adjust the properties of the body, the geometry, and the shape in the Inspector window.

To configure the objects in your script instead, set the properties of the definition object before you create the objects. For more information, refer to Configure 2D physics properties using a definition.
Enter Play mode to run the script and create the objects. Unity displays the shape in the Scene view and Game view as a debug visualization. The line on the shape points towards the rotation direction of the shape.

Note: By default, a physics body is static and isn’t affected by physics. To make it dynamic, in the Inspector window of the GameObject, set Body Type to Dynamic. For more information, refer to Configure objects with definitions.

After you create a shape from geometry, the shape doesn’t change if you change the geometry object.

Example

The following example creates a circle. Attach the script to a GameObject in your scene then enter Play mode to check the shape.

using UnityEngine;
using Unity.U2D.Physics;

public class CreateWorldAndObjects : MonoBehaviour
{
    // Declare definitions that contain default properties for the body and shape
    public PhysicsBodyDefinition bodyDefinition = PhysicsBodyDefinition.defaultDefinition;
    public PhysicsShapeDefinition shapeDefinition = PhysicsShapeDefinition.defaultDefinition;
 
    void Start()
    {
        // Get the default world
        PhysicsWorld world = PhysicsWorld.defaultWorld;

        // Create the physics body with the body definition
        PhysicsBody myObject = world.CreateBody(bodyDefinition);

        // Create the circle geometry
        CircleGeometry circleGeometry = new CircleGeometry { radius = 1.5f };

        // Create the shape with both the geometry and the shape definition
        myObject.CreateShape(circleGeometry, shapeDefinition);
    }
}

Additional resources

Create a world with the Physics Core 2D API

Add a sprite to a Physics Core 2D API object