The Internet of Things (IoT) is a paradigm where real-world entities can be connected to the Internet and provide services with the help of attached devices. With the development of IoT technologies, the number of devices deployed around the world as well as their services are increasing rapidly. Thus, selecting an appropriate service which satisfies a user's requirements from such many services becomes a time consuming challenge. Therefore, to address this issue we propose a Physical Service Model (PSM) to describe heterogeneous IoT physical services. PSM contains three core concepts (Device, Resource and Service) and specifies their relationships. Based on PSM, we define four quality of service (QoS) attributes and rate candidate services according to user requirements. In order to dynamically aggregate individual QoS ratings and select physical services, we propose a Physical Service Selection (PSS) method which takes a user preference and an absolute dominance relationship among physical services into account. Finally, experiments are conducted to evaluate the performance of the proposed method.