Measured in Ohms W
Measured with a ohmmeter.
Need to push electrical current through a resistor. The more current you want the greater the push. This can be expressed mathematically as V=IR where V is the voltage, I is the current and R is the resistance.
Modeled by imagining a resistor as a bottleneck for flow. Experiment with different size straws. The harder you blow the more air you can push through the straw and the smaller the straw opening the harder it is to blow air through it.
Ideal component that serves as a resistor has the diagrammatic representation: