Physics Education Research (PER). Open questions in PER: What is the nature of student understanding (or misunderstanding) of a particular physics topic? How to measure student understanding? How does understanding evolve with time? What role do general cognitive mechanisms play? What is the most effective way to teach a particular topic? Why are some teaching methods better than others? How to implement instructional methods on a large scale? In the past I have worked more specifically with student understanding and learning mechanisms in relation to physics and in Assessment and Curriculum design.