# Introduction to constraints

> Learn what a Physics Constraint component does, and understand motors, springs, and the seven types of constraint you can use to connect 2D Physics Core objects.

Learn what a Physics Constraint component does, and understand motors and springs.

> **Note:**
>
> This documentation is about using Pose, Area, and Constraint components. To use 2D physics in the Unity Editor using components like the Rigidbody 2D component, refer to [2D physics](/engine/6000.7/manual/unity2d/2d-physics.md.md) instead.

A Physics Constraint component connects two objects. Most constraints force two objects to stay at a fixed distance, or rotate them around a point.

For example, you can create a fixed constraint that welds two objects together, or a distance constraint that keeps them a set distance apart. Use constraints to simulate real-world mechanical behaviours like a spring or a hinge.

Most constraints allow you to set the anchor points on the objects they connect, and limits on the force and torque they apply.

## Constraint types

2D Physics Core provides seven types of Physics Constraint component.

| **Constraint type**         | **Description**                                                                                                                                          |
| --------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Physics Constraint Distance | Tries to keep two connected objects a certain distance apart.                                                                                            |
| Physics Constraint Fixed    | Tries to keep the two connected objects at the same position and rotation.                                                                               |
| Physics Constraint Hinge    | Places two objects at the same location, and allows the second object to rotate while connected to the first.                                            |
| Physics Constraint Ignore   | Prevents collisions between two objects, and otherwise doesn't affect the objects or their movement.                                                     |
| Physics Constraint Relative | Moves and rotates objects opposite to each other.                                                                                                        |
| Physics Constraint Slider   | Allows one object to restrict a second object so it can only slide along one axis. The rotation of the first object defines the axis.                    |
| Physics Constraint Wheel    | Pins two objects together, for example a suspension object and a wheel. You can then rotate the second object with a motor so it moves along the ground. |

## Motors and springs

Most constraints let you configure the following in the **Definition** section of their Editor window. Each one is a collapsible group that's closed by default.

* A **Limit** group that restricts how far the connection stretches.
* A **Spring** group that adds an invisible spring to make the connection springy instead of rigid.
* A **Motor** group that adds an invisible motor. The motor acts like a winch to pull or push the two connected objects.

For more information, refer to [Add a constraint](/engine/6000.7/manual/unity2d/2d-physics-api/connect-objects/create-constraint.md).

## Additional resources

* [Physics Pose and Physics Area components](/engine/6000.7/manual/unity2d/2d-physics-api/create-objects/pose-and-area.md)
* [PhysicsCore2D repository](https://github.com/Unity-Technologies/PhysicsExamples2D/tree/master/PhysicsCore2D) on GitHub