I’m primarily talking about stuff like step counters, but also health apps measuring your heart rate, how many stairs you take, the length of your steps, and so on. I’m honest when you tell me to explain it to me like I’m five years old, this one boggles my mind.
B is the magnetic field. Both B and E fields generate measurable forces.
In particular, magnetic forces require the charge to be moving. If v = 0, the term v × B = 0, i.e. it disappears. The equation above is really why magnets are able to do stuff.
Some materials are just naturally “more chill with” having its charges magnetized into motion. These are your permanent magnets. Electromagnets use an external source to generate an electric current, which is charge in motion, which generates the magnetic field.
It’s wildly more complicated than that, like it’s literally several college courses, but IMO that’s the gist of it.