It was a simple principle. And it worked.The little red plastic car had a magnet in it. Another magnet was molded in the hand-held piece shaped to fit two fingers. Two tiny fingers.“Remember how I showed you,” I recall her telling me. “Do it the way you’re supposed to, and it will work.”I sighed and tried it again. The way she had told me to do it in the beginning. And just like magic, when I waved my hand over the toy car, it rolled across the tabletop. Propelled by the scientific principle of opposing magnetic fields.My dad’s mom spent ...