Unity: OnTriggerEnter vs. OnCollisionEnter

The rule of thumb: Use OnCollisionEnter for physical impacts (bouncing, stopping, pushing) and OnTriggerEnter for spatial overlap (passing through).

The Golden Rule for Both

To fire either event:

Both objects must have a Collider.
At least one object must have a Rigidbody.

Feature	`OnCollisionEnter`	`OnTriggerEnter`
`Is Trigger` Setting	OFF on both colliders.	ON on at least one collider.
Physical Reaction	Yes (objects block, bounce, or slide).	No (objects pass directly through).
Performance Cost	Higher (calculates forces and contacts).	Lower (only checks bounding box overlap).
Best For	Walls, bouncing projectiles, pushing crates.	Collectibles, checkpoints, aggro/dead zones.

Quick Code Reference

// 1. Physical Impacts (Solid Colliders)
private void OnCollisionEnter(Collision collision)
{
    // Access impact force and exact contact points
    float force = collision.relativeVelocity.magnitude;
    Debug.Log($"Hit {collision.gameObject.name} with force: {force}");
}

// 2. Overlap Detection (Trigger Colliders)
private void OnTriggerEnter(Collider other)
{
    // 'other' is the specific collider that passed through the zone
    if (other.CompareTag("Player"))
    {
        Debug.Log("Player entered the zone!");
    }
}