transistor
"From our water analogy, the width of a pipe is similar to the resistance in a circuit. If a valve can finely adjust the width of a pipe, then a transistor can finely adjust the resistance between collector and emitter. So, in a way, a transistor is like a variable, adjustable resistor. "
"A transistor is like a valve, but you use electricity to open or close it," explained Arun Majumdar, professor of mechanical engineering at UC Berkeley. "Here, we use a voltage to open or close an ion channel. Now that we've shown you can make this building block, we can hook it up to an electronic chip to control the fluidics."
"A transistor is like a pressure-activated valve. There are three wires into it; if voltage is applied to one of them then current can flow between the other two."
"The transistor is like a relay - a switch which is controlled by another switch. This is the fundamental logic unit."
A nice simple overview of computers
METAMIA is a free database of analogy and metaphor. Anyone can contribute or search. The subject matter can be anything. Science is popular, but poetry is encouraged. The goal is to integrate our fluid muses with the stark literalism of a relational database. Metamia is like a girdle for your muses, a cognitive girdle.