Now that we have definitions of current and voltage, we can see how, when we vary the voltage across a circuit element, how the current in that circuit element changes. We tested a couple of different resistors and the long bulb from the CASTLE kit:
Most of us saw nice, straight lines for resistors and the long bulb, but once we realized that, when the voltage is zero, the current has to be zero, it made sense that not every circuit element could be represented by a straight line that went through (0,0). So now we have Ohm's Law.