KFUPM PYP-English Technology 1 Podcasts
Technology 1 Unit 5 Appropriate Technology
Appropriate technology is technology which uses locally available materials and expertise to provide inexpensive solutions to problems in countries in the developing world, particularly in poorer rural areas. The wind pump is a typical example — it is relatively simple to construct and maintain, and does not require fuel. It contains a simple mechanism, a crankshaft, which converts the rotary (round and round) movement of the blades into a reciprocating (up and down) movement which, in turn, is linked to the piston of a pump.
The clockwork radio is a more sophisticated example. It consists of a clockwork motor which drives a small generator. This produces enough power to run the radio. The step-up gears increase the speed of rotation of the motor. The radio is cheap to use because it does not need mains power or batteries, which can be very expensive. The clockwork computer described in the Gadget box uses the same form of power. Its cost is kept low because the computer is not advertised, and it uses open-source software, which is available free to anyone (unlike Microsoft, for example, which requires users to pay for a licence).
Portable generators combine an engine, usually diesel, with an electric generator. They provide power in emergencies or in areas where no mains power is available, but are often very noisy. Noise is measured in decibels (dB) — the higher the number, the noisier the machine. At home, the generator may be used to power domestic appliances such as kettles, freezers, washing machines, and air conditioners. The amount of electricity they use is measured in kilowatts (kW). Lighting uses much less electricity.
Car engines are normally four-stroke. In a four-stroke petrol engine there is a cycle (or series) of events which is completed in four strokes (or movements) of the piston: on the induction stroke, the fuel is drawn into the cylinder, on the compression stroke, the fuel is compressed and ignited by the spark plug, on the power stroke, the piston is driven down the cylinder by the expanding gas from the burning fuel, and on the exhaust stroke, the rising piston pushes the exhaust gas out of the engine.
Two-stroke engines are used in portable devices such as chainsaws. They can be used at any angle. Put simply, in the two-stroke cycle, power and exhaust are combined in one stroke, compression and ignition in the other. There is no requirement for inlet and outlet valves for entry of the fuel or exit of the exhaust gas. This simplifies construction and reduces the cost of two-stroke engines. However, they are noisy and produce more pollution than four-stroke engines.
jeudi 10 mars 2011
podcasst from Oxford English for Careers, Technology 1 Teacher’s Resource Book  Oxford University Press, 2007, by David Bonami; with additional material by Norman Glendinning