Friction Joint 2D fundamentals

Use the Friction JointA physics component allowing a dynamic connection between Rigidbody components, usually allowing some degree of movement such as a hinge. More info
See in Glossary 2D to slow down movement between two points to a stop. This joint’s aim is to maintain a zero relative linear and angular offset between two points. Those two points can be two RigidbodyA component that allows a GameObject to be affected by simulated gravity and other forces. More info
See in Glossary 2D components or a Rigidbody 2D component and a fixed position in the world. (Connect to a fixed position in the world by setting Connected Rigidbody to None).

Resistance

The joint applies linear force (Force) and angle force (Torque) to both Rigidbody 2D points. It uses a simulated motor that is pre-configured to have a low motor power (and so, low resistance). You can change the resistance to make it weaker or stronger.

Strong Resistance:

• A high (1,000,000 is the highest) Max Force creates strong linear resistance. The Rigidbody 2D 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
  See in Glossary won’t move in a line relative to each other very much.
• A high (1,000,000 is the highest) Max Torque creates strong angular resistance. The Rigidbody 2D GameObjects won’t move at an angle relative to each other very much.

Weak Resistance:

• A low Max Force creates weak linear resistance. The Rigidbody 2D GameObjects move easily in a line relative to each other.
• A low Max Torque creates weak angular resistance. The Rigidbody 2D GameObjects move easily at an angle relative to each other.

Constraints

Friction Joint 2D has two simultaneous constraints:

• Maintain a zero relative linear velocity between two anchor points on two Rigidbody 2Ds
• Maintain a zero relative angular velocity between two anchor points on two Rigidbody 2Ds

You can use this joint to construct physical GameObjects that need to behave as if they have friction. They can resist either linear movement or angular movement, or both linear and angular movement. For example:

• A platform that does rotate, but resists applied forces, making it difficult but possible for the player to move it.
• A ball that resists linear movement. The ball’s friction is related to the GameObject’s velocity and not to any collisionsA 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
  See in Glossary. It acts like the Linear Drag and Angular Drag which is set in Rigidbody 2D. The difference is that Friction Joint 2D has the option of maximum Force and Torque settings.

Additional resources

• Joints 2D
• Friction Joint 2D component reference