https://turbowarp.org/930116954?clones=Infinity Mouse moves magnet. "Iron filings" show magnetic field. You can turn off mouse-controlled.
Faraday noticed iron filings line up to form "magnetic lines of force" around magnets. This led to today's concept of "magnetic field lines." To overcome Scratch's limit of 300 clones (iron filings): https://turbowarp.org/930116954?clones=Infinity