Use only the attached Pendulum Source Packet and fictional observation sheet. Make a 90-second student explainer about what changes a pendulum’s period. First give four verified facts with source IDs. Explain that the small-angle model depends on length and gravity, not bob mass. Distinguish a complete oscillation from a one-way swing. Label the classroom observations fictional. Do not invent a curriculum code or measurement. Finish with a prediction question, an answer and one model limitation. I will check the facts before generating media.