OnCollisionEnter2D and OnTriggerEnter2D in Unity - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is OnCollisionEnter2D used for in Unity?

OnCollisionEnter2D is a method called when two 2D physics objects with colliders and rigidbodies physically collide. It detects solid collisions.

beginner

How does OnTriggerEnter2D differ from OnCollisionEnter2D?

OnTriggerEnter2D is called when a collider marked as a trigger overlaps another collider. It detects overlaps without physical collision response.

intermediate

What must be true about colliders for OnTriggerEnter2D to be called?

At least one collider must have Is Trigger enabled, and at least one object must have a Rigidbody2D.

intermediate

What parameters does OnCollisionEnter2D receive and what info can you get from it?

It receives a Collision2D object, which contains info like the other collider, contact points, and relative velocity.

beginner

Why would you use OnTriggerEnter2D instead of OnCollisionEnter2D?

Use OnTriggerEnter2D to detect when objects overlap without blocking movement, like picking up items or entering zones.

Which method is called when two solid 2D objects collide physically?

A OnCollisionEnter2D

B OnTriggerEnter2D

C OnOverlapEnter2D

D OnContactEnter2D

OnCollisionEnter2D is triggered by physical collisions between 2D colliders.

What must be enabled on a collider to use OnTriggerEnter2D?

A Is Solid

B Is Trigger

C Is Kinematic

D Is Static

The collider must have Is Trigger enabled to detect overlaps without physical collision.

Which component is required on at least one object for collision or trigger events to work?

A Rigidbody2D

B BoxCollider2D

C SpriteRenderer

D Animator

A Rigidbody2D is needed to detect physics collisions or triggers in Unity 2D.

What kind of information does the Collision2D parameter provide in OnCollisionEnter2D?

A The trigger zone size

B Only the other object's name

C Contact points and relative velocity

D The object's health

Collision2D gives details like contact points and relative velocity during collision.

When would you prefer OnTriggerEnter2D over OnCollisionEnter2D?

A To change physics materials

B To detect physical impacts only

C To animate sprites

D To detect overlaps without blocking movement

OnTriggerEnter2D is used for detecting overlaps like pickups or zones without physical collision response.

Explain the difference between OnCollisionEnter2D and OnTriggerEnter2D in Unity.

Think about solid hits versus passing through areas.

Describe a simple use case for OnTriggerEnter2D in a 2D game.

Imagine a player walking into a special area or collecting coins.