Summary
Vibrations and Waves
Visualisations
Vibrations and waves is one the topics that first year students find the most difficult, as it is the first new bit of physics they see that wasn't covered in school.
To help build an intuition on this topic, and to answer the question “What exactly are normal modes?”, I've written an online worksheet that guides students through the topic step by step, and at every point letting them interact with the system.