Aerial robots have been widely used as sensor carrying platforms in a wide range of application, mainly because using this type of systems for physical interaction seems to be an unsuitable operation. This is not only due to the risk of collision and damage of the platform, but also because it is unclear whether a consumer-grade UAV can withstand physical contact with the environment. In this paper, we address the issue of performing physical interaction with the environment by a multirotor UAV implementing a basic cascaded position-attitude controller, typical of most of consumer-grade multirotor systems. Precisely, we identify mathematically the boundaries where the system can safely be used to perform physical interaction with the environment. The theoretical approach is finally validated through experiments showing that physical contact can only be achieved within a predefined region of control inputs.