How do telescopic sports car antennas work?

A friend of mine says they are pushed upwards any pnuematically or hydraulically. Is he right? If not, then what is the moving parts?

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Answers:    They are made up of 3 or more pieces of metal shaft inside of each other. Inside specifically a plastic line beside teeth on it. On the bottom of the largest shaft is a motor with teeth as okay. When power is applied to the motor it extends upwards and then reversed when power is taken away.

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They are motorized. Not hydraulic or pnuematic.

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