OnCollisionEnter

The **OnCollisionEnter** method is a built-in function in the Unity game engine used to detect and respond to collisions between colliders in real-time. It is part of the UnityEngine.Physics namespace and is commonly employed in C# scripts attached to GameObjects with colliders. The method is specifically designed to handle collisions that occur when two colliders enter contact with each other, triggering the event once per collision.

When a collision is detected, Unity invokes the **OnCollisionEnter** function, passing a reference to the **Collision** object as an argument. This object contains detailed information about the collision, such as the **ContactPoint**, **relativeVelocity**, **impulse**, and references to the colliders involved (**collider** and **otherCollider**). Developers can use this data to implement physics-based interactions, such as damage systems, object destruction, or triggering events like sound effects or visual feedback.

Unlike **OnTriggerEnter**, which is used for trigger colliders, **OnCollisionEnter** is reserved for rigidbody-based collisions, meaning it only activates when colliders are attached to objects with rigidbody components. This ensures that the collision detection is physics-driven, providing more accurate and realistic interactions. The method is called only once per collision frame, even if multiple contact points exist, though additional contact points can be accessed via the **Collision.contacts** array.

For optimal performance, developers should avoid heavy computations within **OnCollisionEnter**, as it is called frequently during gameplay. Additionally, it is important to properly configure colliders and rigidbodies to ensure collisions are detected as intended. The method is particularly useful in game mechanics requiring precise collision responses, such as platformers, vehicle physics, or puzzle-solving interactions.