The Relationships These Model
Velocity is displacement over time — and displacement is not distance. This distinction is the whole reason the tool is worth using rather than dividing in your head. Displacement is the straight-line change in position from start to finish, including direction; distance is the total path travelled. Drive 50 miles out and 50 miles back in two hours and your average speed is 50 mph, while your average velocity is exactly zero, because you ended where you started. Velocity is a vector; speed is a scalar. Physics problems that seem to give absurd answers are frequently just enforcing this difference.
Average velocity says nothing about the journey. It describes the net result over an interval, not what happened during it. An object that accelerated, stopped, and reversed can share an average velocity with one that cruised steadily. For anything about the moment rather than the interval you need instantaneous velocity, which is where calculus enters the subject.
Ohm's Law is one relationship with three faces. V = I × R, rearranged as I = V/R or R = V/I depending on what you know. Its practical power is that in any simple resistive circuit, two measured quantities give you the third without further measurement — which is why it is the first thing anyone learns with a multimeter, and why fault-finding usually starts there.
Ohm's Law is a model, and real components disobey it. It holds for ohmic conductors where resistance stays constant. Real resistance rises with temperature in most metals, and semiconductors, diodes and filament lamps are frankly non-ohmic — a bulb's cold resistance is a fraction of its hot resistance, which is precisely why filaments fail at switch-on rather than during steady use. The law is exact for the idealised case and an approximation for the messy one.