For questions regarding the physics relevant to fictitious worlds. General physics may be off-topic.
Physics is the study of observable things of all scales from a single elementary particle to the entire universe. This tag is often used for questions regarding events that may break the 'normal' laws of physics, and could be used in conjunction with reality-check to determine whether or not an event violates said laws. It can also be used to refer to new laws of physics created for a fictional world. Consider also the science-based or hard-science tags.
Be careful if asking about the laws of physics as they exist in our current universe: such questions, if posed without a clear worldbuilding aspect, are off topic and may be migrated to Physics.SE.