Question

why does spinning a wooden stick between two rocks ignite?//

Answer 1

As friction, heat and pressure are being applied to the wooden stick by the rocks and with your body, the wooden stick will start to generate embers, or smoking powder as it begins to wear out due to the friction with the rocks. As little pieces are generated by friction, it will be easier for them to ignite with the temperature and pressure conditions given by spinning the stick against the rocks. Also, the rocks are good for keeping the temperature generated by the friction.