rigidbody2d does not follow physical rules

Hi Guys,

I´ll facing a problem, which I can´t handle since days (I am a beginner in Unity). What I managed and was working to draw a line and adding an EdgeCollider2D with script. (It´s working fine (as soon the ball hit´s the line it´s moving it´s direction)).

Now I wanted the line to fall down (some kind of gravity). I did this with adding an Rigidbody2D.

So and this is my problem: The line falls down and hit´s the ground (my ground is for example a BoxCollider2D). As soon it hits the ground it´s moving around with no physical rules (look´s like it´s dancing ). Sometimes it´s just thrown through the screen. I want the line to stay on the ground.

For example: if I draw a triangle it should fall down to the boxCollider2D and should simply stay on the ground (currently it´s slightly moving in the x-axis) (see picture)

Does anybody know what´s my fault, or what to do?

Thanks in advance. Tobi.