Anatomical parahomology "Let the waters", it is said, "bring forth abundantly moving creature that hath life and fowl that may fly above the earth in the open firmament of heaven. Because there is, so to say, a family link between the creatures that fly and those that swim. In the same way that fish cut the waters, using their fins to carry them forward and their tails to direct their movements round and round and straightforward, so we see birds float in the air by the help of their wings. Both endowed with the property of swimming, their common derivation from the waters has made them of one family.
Paradigms[ edit ] There is no unique paradigm for establishing this analogy. Two paradigms can be used to introduce the concept to students using pressure induced by gravity or by pumps.
In the version with pressure induced by gravity, large tanks of water are held up high, or are filled to differing water levels, and the potential energy of the water head is the pressure source. This has the advantage of associating electric potential with gravitational potential.
A second paradigm is a completely enclosed version with pumps providing pressure only and no gravity. This is reminiscent of a circuit diagram with a voltage source shown and the wires actually completing a circuit. This paradigm is further discussed below.
Other paradigms highlight the similarities between equations governing the flow of fluid and the flow of charge. Flow and pressure variables can be calculated in both steady and transient fluid flow situations with the use of the hydraulic ohm analogy. The pressure and volume flow variables are treated as phasors in this definition, so possess a phase as well as magnitude.
In this paradigm, a large cavity with a hole is analogous to a capacitor that stores compressional energy when the time-dependent pressure deviates from atmospheric pressure. A hole or long tube is analogous to an inductor that stores kinetic energy associated with the flow of air.
Hydraulic analogy with horizontal water flow[ edit ] Voltage, current, and charge[ edit ] Hydraulic pressure difference In general, electric potential is equivalent to hydraulic head. This model assumes that the water is flowing horizontally, so that the force of gravity can be ignored.
In this case electric potential is equivalent to pressure. The voltage or voltage drop or potential difference is a difference in pressure between two points.
Electric potential and voltage are usually measured in volts. Electric current is equivalent to a hydraulic volume flow rate ; that is, the volumetric quantity of flowing water over time. Usually measured in amperes.
Electric charge is equivalent to a quantity of water. Basic circuit elements[ edit ] Conducting wire: Node in Kirchhoff's junction rule: A pipe tee filled with flowing water.
A relatively wide pipe completely filled with water is equivalent to conducting wire. When comparing to a piece of wire, the pipe should be thought of as having semi-permanent caps on the ends.
Connecting one end of a wire to a circuit is equivalent to un-capping one end of the pipe and attaching it to another pipe. With few exceptions such as a high-voltage power sourcea wire with only one end attached to a circuit will do nothing; the pipe remains capped on the free end, and thus adds nothing to the circuit.
A resistor is equivalent to a constriction in the bore of the pipe which requires more pressure to pass the same amount of water.The cell is the basic unit of a living organism. In multicellular organisms (organisms with more than one cell), a collection of cells that work together to perform similar functions is called a tissue.
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Interactive animation showing how ATP functions like a rechargeable battery in the transfer of energy. Analogy: A kind of extended metaphor or long simile in which an explicit comparison is made between two things (events, ideas, people, etc.) for the purpose of furthering a line of reasoning or drawing an inference; a form of reasoning employing comparative or parallel cases..
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