One popular advanced technology nowadays is smartphone. Smartphones allow various functions beyond the traditional function of mobile phones as communication devices. The technology in smartphones has potential applications in many areas including education. In this study, we report our research which aims to: (1) produce a smartphone app as media for learning Impulse-Momentum; (2) determine the appropriateness and quality of the app; and (3) describe the effectiveness of the smartphone app to help students in learning the concept of Impulse-Momentum. We use developmental research method within 4D (define, design, develop, disseminate) model. The smartphone app is reviewed by physics education expert and teacher. The field testing involves a group which consists of 26 high school students. The students are given pre- and post-tests before and after they use the developed learning media, respectively. It aims to investigate the impact of the media to students' conceptual understanding. The normalized gain (N-gain) score of their pre- and post-tests is 0.74 which can be categorized as high improvement.