Rigidbody2d.velocity turn to zero when hit collider?

hi all,i move the rigidbody2d by velocity,but not fall down when hit collider,why?

Vector2 vv=new Vector2(dir.x*force,rigidbody2D.velocity.y);
rigidbody2D.velocity=vv;

Nobody met this problem?

Sounds like you’re pushing the object against a surface which has friction thus resists it moving downwards. Use PhysicsMaterial2D that has zero friction.

but not give physics material 2d to any collider,I think that should no friction

If you don’t assign a physics material to a collider, then the default one is used. If no default is assigned then the defaults are bounce=0 and friction=0.4

ok,got it ,thank u!