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Question by Reaverb0t · Sep 03, 2021 at 01:09 AM · 2dphysicsvelocitybounce

How do I get velocity from a collision?

I am simply trying to get the velocity that an object collides with, so that it can inherit that velocity. I am new to scripting.

Basically I have a ball and two paddles (imagine something 2D like pong with similar graphics but you can move closer and farther away). If the player charges towards the ball while the paddle is moving in, the ball will pass right through it and not bounce off. This causes the ball to slow down to a crawl.

If there is an easier way to do achieve this please let me know.

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Answer by AlbieMorrison · Sep 03, 2021 at 12:45 PM

You can get the relative velocity between the two colliding objects and bounce the ball back by doing this, in the script that controls the ball:

 void Start()
 {
     Rigidbody2D rb = GetComponent<Rigidbody2D>();
 }
 
 OnCollisionEnter2D(Collision2D collision)
 {
     Vector2 velocity = collision.relativeVelocity;
     rb.velocity = Vector2.Reflect(velocity,Vector2.right/*make this a Vector2 pointing 90 degrees from your paddle surface*/);
 }


Also make sure you have a Rigidbody2D on at least the ball and probably both paddles as well, with the appropriate colliders for their shapes. I believe you will need to freeze the rotation and position in all directions of the Rigidbodies. Hopefully this helps!

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avatar image Reaverb0t · Sep 04, 2021 at 04:57 PM 0
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I have never heard of Reflect before. Can you explain what this means from the manual? https://docs.unity3d.com/ScriptReference/Vector2.Reflect.html


public static Vector2 Reflect(Vector2 inDirection, Vector2 inNormal);


What is inDirection and what is inNormal? Thank you.

avatar image ahsen35813 Reaverb0t · Sep 05, 2021 at 03:01 PM 0
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inDirection would be the velocity vector of the object co$$anonymous$$g into the collision, and inNormal would be the vector pointing perpendicular to the surface of the collision (also known as the normal)

avatar image AlbieMorrison Reaverb0t · Sep 05, 2021 at 03:31 PM 0
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Vector2.Reflect() takes a vector and reflects it around the isNormalvector, using the inDirection vector as the vector to reflect. So effectively, whatever the angle between the two vectors, it takes that and returns a new vector with the same angle away from isNormal only on the opposite side.

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