my player slips on ground

i add force to my character by player.rigidbody2D.AddForce (Vector3.right * 45); every frame .it works but when the player walks and i change his direction to opposite he slips on ground and then he changed his position. i try to add player.rigidbody2D.velocity = new Vector3(0, 0, 0); somehow it work but when the character stops he goes a bit back and forth.and i dont know why.i think i should change physics setting but don't know which should i change.maby friction...