This work describes the investigations on how designers communicate functionality of articulated product concepts through sketching. Sketching has been used by designers to explore concepts in the early phases of design. In articulated product concept sketches, the ideas represented through sketching goes through several iterations before it is realized into physical products. This iterative process increases the overall product development time. One of the primary reasons for a longer product development cycle is that there is a great difficulty in visualizing motions of articulated product concepts through sketching. Designers use annotations to represent motion details which need to be validated for physically realizable ideas. To study this, design experiments were conducted which involved four designers to sketch concepts for an articulated product. Think-Aloud protocol analysis methodology was followed. The sketching activity is video recorded and transcribed with a modified coding scheme for sketch analysis. To quantify the amount of effort in representing motion, a measure of effort metric is introduced which is derived from the coding scheme. The analysis shows that there is considerable amount of effort from the designers in representing the motion in their sketches. It is also observed that conventional paper-based sketching does not support complex motion explorations. These observations form the basis for development of novel sketch-based interfaces to support a variety of explorations of articulated product concepts. © Proceedings of the NordDesign 2020 Conference, NordDesign 2020. All rights reserved.