Science Fair Project Encyclopedia
The term "trolley" derives from the trolley pole that collects live power from an overhead wire or cable, sometimes simply strung, sometimes as catenary. The trolley pole in turn derived its name from the "trolley wheel" that was formerly the chief means of contact between car and wire as the wheel "trolled" behind the moving car.
Modern trolleys often do not use a trolley wheel (using a metal shoe with a carbon insert instead) or even a trolley pole, a pantograph being the preferred means of contact. Other streetcars are sometimes called trolleys, even though this may be technically incorrect, as for a cable car or a conduit car that drew power from an underground third rail. Trolleys and trolley lines are also often described as light rail, especially if the line has significant off-street running.
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