Multiple representations are valuable tools used to help students learn how to think like physicists and understand physics concepts. Generally, in case of teaching students’ understanding of collisions, one of the available options is using the momentum bar charts. They can clearly represent the magnitude of the momentum before and after collision but they cannot be used to represent directions. This work shows a new but conventional and important representation—the momentum vector diagrams—teachers can use to help students apply conservation of momentum in two-dimensional collision. The momentum vector diagrams were used to teach grade-10 students at a school in Bangkok in 2015. The other group of students at the same school was taught traditionally using conservation of momentum equations without drawing any momentum vectors. The post-test results revealed that the former group performed better in solving two-dimensional collision problems. In addition, students who learned with momentum vector diagrams realized more that the situation in the problem was two dimension.
Keyword: momentum vector diagram, two-dimensional collision, conservation of momentum.