Ohm's law (V=IR) defines the voltage–current–resistance relationship — the foundation of circuit analysis, grasped via the water-flow analogy and used to estimate motor current in the kickboard BLDC.
The law via the water-flow analogy
V is water pressure, I is flow, R is a narrow pipe — that mapping is the entire intuition of V=IR.
12V across 6Ω gives I = 2A; current loops the closed circuit and R sets how much flows.
The supply fixes V, so the designer's knob is R — raise it to limit current.
V=I×R
V
Voltage = pressure
I
Current = flow
R
Resistance = narrow pipe
12V ÷ 6Ω = 2A
Kickboard / STM32 context
Motor coil: estimate max current V/R to judge torque and burnout risk.
Shunt resistor: measure the small voltage across a small R to back-calculate current.
LED protection resistors deliberately add R to cap current; MOSFET heat estimates use the same relation.
Pitfalls & gotchas
Real motor coils also have inductance, so current never changes instantly; at high current even wiring resistance causes voltage drop and heat.