Phys. Teach. 59, 683 (2021); https://doi.org/10.1119/5.0025840 59, 683 © 2021 Author(s). Using Math in Physics: 4. Toy models Cite as: Phys. Teach. 59, 683 (2021); https://doi.org/10.1119/5.0025840 Published Online: 19 November 2021 Edward Redish