2d physics - get a shot object to bounce back off a wall

Questions & Answers
1

I am trying to implement a 2d physics game where fired projectiles have mass and can move objects when they hit them (like the game Exile on the BBC Micro which is what I’m basing my engine on). Considering the situation below where an object is resting against a wall:

89487-wallprob.jpg
89487-wallprob.jpg726×422 8.06 KB

The red player fires a projectile (along the path of the arrow) at the green box. I would like the wall to ‘absorb’ a certain amount of the impact, but then have the box bounce back off the wall. however no matter what settings I try for the physics material for the wall and/or the box, the box just stays stuck against the wall rather than bouncing back (have tried setting bounciness to 1 + messed with linear & angular drag on the box). The box has freeze Z rotation on, however even with it off it won’t budge. The box and projectile have BoxCollider2d’s (and RigidBody2Ds) on them. The wall has a PolygonCollider2D but no RigidBody2D. The projectile is destroyed as soon as it hits the box.

Is there any way to get the box to bounce back off the wall? Similarly, if the player is standing on the box and shoots at the left corner, it should move left slightly but it also won’t move. Friction doesn’t seem to work as expected or I’m doing something dumb. I’m using AddForce for the initial launch of the projectile.

2

It looks like regular physics to me.
If a real life box was standing against that wall, bouncy as it was, would it bounce off the wall if hit from a small projectile like in your drawing?

So, a couple of things I’d change is:

  1. Move the box away from the wall, allowing it to gather momentum
  2. Raise the mass of the projectile significally
  3. Lower the mass of the box

Also maybe I would try to use a SliderJoint2D on the box. It might give you the effect you’re looking for.