Voltage can be thought of as the pressure pushing charges along a conductor, while the electrical resistance of a conductor is a measure of how difficult it is to push the charges along. Using the flow analogy, electrical resistance is similar to friction. For water flowing through a pipe, a long narrow pipe provides more resistance to the flow than does a short fat pipe.
Resistance also depends on temperature, usually increasing as the temperature increases.
For reasonably small changes in temperature, the change in resistivity, and therefore the change in resistance, is proportional to the temperature change. The connection between voltage and resistance can be more complicated in some materials. These materials are called non-ohmic. We'll focus mainly on ohmic materials for now, those obeying Ohm's Law. A copper wire has a length of 160 m and a diameter of 1.00 mm.