![]() An even more abstract view is provided by a description in terms of stores – one that is even less concerned with the how?, and so even more focused on the how much?. Then the device/pathway description provides a useful level of detail for one strategic view of the engineering demands. Use a battery to drive a motor, which is lifting a pallet (perhaps on a fork-lift truck). A perfect motor will switch all of the power – there is no waste. A motor is simply a device designed to switch from an electrical pathway to a mechanical pathway, so it's a kind of a transducer. Nevertheless, if robots are to play any part in the future, there will be a great need for engineers to design motors with a range of precision and rated power.īut there is a simpler view (and physicists like simpler views) that provides guidance for all of this engineering. ![]() Perhaps flash memory players will supersede both hard disks and portable audio cassette players, with their need for very precise motors to draw the tape over the head at 1 7 8 inches per second. The reproduction of music has depended on precise rotation from 78 rpm (revolutions per minute) singles, through the steady high speed for audio CD-ROM, to the steady high speed for hard disk drives (7200 rpm is commonly available at the time of writing). Precision movement is required for the last example – but perhaps not for much longer. Even in the domestic sphere you can find motors designed to agitate clothes in a washing machine, blend soup, grind coffee or to spin the hard disk in your portable music player. There are many working powers for motors. This accumulation can be either positive or negative, thereby augmenting or depleting the energy in the store.įor the electrical pathway, you choose how to make the power larger: set the character of the pathway by using either a larger current or a larger potential difference, or both.Īccumulating over more time, at the same constant rate, also leads to larger quantities of energy being shifted to or from stores. Constant power implies steady rate of accumulationĪ larger constant power in any pathway accumulates energy in a store at a larger steady rate. This is the view that was emphasised in the earlier SPT: Energy and SPT: Electric circuits topics. ![]() In both locations the device will not be perfect – there will be some switching to other pathways, chiefly heating by particles as the water is warmed by churning through the turbine, and the wires in the generator are warmed by the current driven through them, as the air surrounding the lamp is warmed.ĭescribing the process in terms of energy shifted, you end up with an even more abstract picture, as the gravitational store is depleted and the thermal store augmented. The system is designed to optimise the following switches: at the generator, from the mechanical pathway to the electrical pathway at the lamp, from the electrical pathway to the heating by radiation pathway (again, visible radiations only – that is our particular interest because of how we evolved). Then there are only two devices in the circuit – places where pathways are switched. Model the circuit, simplifying as much as possible, with wires of negligible (as near to zero as makes no difference) resistance. This accumulation can be either positive or negative.Īs a starting example, use a simple large-scale electrical loop that does something useful: a hydro-electric generator, deep in the Welsh countryside, lights a domestic lamp in the West Midlands. So a constant power in a pathway leads to a steady accumulation in a store. The power in this pathway shifts energy to or from a store, adding to or subtracting from the energy already in the store.
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