Work, Energy and Power
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If the force is in the opposite direction as the displacement, then the angle is degrees. If the force is up and the displacement is to the right, then the angle is 90 degrees.
This is summarized in the graphic below. Power Power is defined as the rate at which work is done upon an object. Like all rate quantities, power is a time-based quantity.
Power is related to how fast a job is done. Two identical jobs or tasks can be done at different rates - one slowly or and one rapidly. The work is the same in each case since they are identical jobs but the power is different. The equation for power shows the importance of time: Special attention should be taken so as not to confuse the unit Watt, abbreviated W, with the quantity work, also abbreviated by the letter W. Combining the equations for power and work can lead to a second equation for power.
A few of the problems in this set of problems will utilize this derived equation for power. Mechanical, Kinetic and Potential Energies There are two forms of mechanical energy - potential energy and kinetic energy. Potential energy is the stored energy of position. In this set of problems, we will be most concerned with the stored energy due to the vertical position of an object within Earth's gravitational field. Kinetic energy is defined as the energy possessed by an object due to its motion.
An object must be moving to possess kinetic energy. The amount of kinetic energy KE possessed by a moving object is dependent upon mass and speed. The total mechanical energy possessed by an object is the sum of its kinetic and potential energies. Work-Energy Connection There is a relationship between work and total mechanical energy. The final amount of total mechanical energy TMEf possessed by the system is equivalent to the initial amount of energy TMEi plus the work done by these non-conservative forces Wnc.
The mechanical energy possessed by a system is the sum of the kinetic energy and the potential energy. Positive work is done on a system when the force doing the work acts in the direction of the motion of the object.
Negative work is done when the force doing the work opposes the motion of the object. When a positive value for work is substituted into the work-energy equation above, the final amount of energy will be greater than the initial amount of energy; the system is said to have gained mechanical energy. When a negative value for work is substituted into the work-energy equation above, the final amount of energy will be less than the initial amount of energy; the system is said to have lost mechanical energy.
There are occasions in which the only forces doing work are conservative forces sometimes referred to as internal forces. These are complex models and demand — as a minimum — a well documented geographic information system GIS of the city.
For this reason, models are not yet much in use, but this is a field of research which should be prioritised so that townships can avail themselves of relatively simple simulation tools.
FSC (Field Studies Council) - Urban ecosystems
They could then improve planning and interaction between the two major areas of public policy which can direct urban growth along sustainable paths: They are summed up in Figure 7 which describes the "pincer movement" of complementary policies capable of controlling transport emissions in emerging cities.
The urban passenger transport emission reducing policies"pincer". Transport policies 63Progressing from the most superficial to the most deep-rooted urban transport-related emission determinants, i.
Improving vehicles and economic instruments 64The main measures that can be taken to improve the environmental efficiency of vehicles are the following: Improving the quality of road infrastructure which has a direct effect on the energy consumption per kilometre of the various types of road vehicles.
Improving fuel quality and introducing low-pollution fuels natural gas, LPG, ethanol, methanol, etc. An example of a t They are of course advisable but they can lead to a significant increase in the cost of urban transport, for the poor in particular who are intensive users of highly polluting and dilapidated shared taxis, buses and rickshaws.
Unless there is some alternative means of transport, cleaner but just as cheap, this kind of policy may be good for the environment but not so good for the poorer citizens, hence a dilemma. It does however turn out well in some cases, as exemplified by the relative success obtained in Delhi when buses and rickshaws transferred to gas. In a study at the request of GTZ, Assmann and Sieber discuss these measures and demonstrate that, with a few exceptions, their efficiency in fighting greenhouse effects is limited, even when the price of oil is high.
The promotion of Mass Rapid Transit MRT 68The urban structure of many cities in the South is, fortunately, still well suited to transport systems based on transit corridors. Urban development is often channelled by the major roads and not too scattered over the whole urban area.
Even severely congested cities are more often car-saturated than morphologically dependent on cars, as yet. Contrary to car-dependent cities with highly scattered activities, in this context major passenger flows can be organised and it is therefore possible to develop Mass Rapid Transit systems. MRTs have a greater capacity than traditional public transport buses, vans, "busetas", shared taxis, etc. MRTs are always provided with infrastructure to allow integration with other transport modes.
Metro systems, heavy or light are still fairly rare in cities of the South, but there is currently general enthusiasm in favour of BRT technology, particularly since it was rediscovered successfully in the capital of Colombia, Bogota. Experience has shown that it is possible to cover the cost of operating heavy rail systems in high density urban areas, but they generally need large public subsidies.
Because of its high cost, heavy rail does not meet the needs of rapidly expanding cities of the South 7. LRTs generally include tramways, although these often run among other traffic without the benefit of exclusive corridors.
Light Rail Transit seems more suitable for prosperous cities. Their capacity is equivalent to that of BRTs, but they seem to be on the wane in cities of the South. It differs from the two metro types because its carriages are heavier, it has longer routes and the tracks are generally part of an older rail system. BRTs operate using high technology buses along exclusive corridors, generally at street level. Their passenger boarding and discharging systems are fast.
They use efficient ticketing methods at the entrance of comfortable stations, on-board technology for monitoring and managing operations, on-line passenger information systems and infrastructure for modal integration. BRTs are much more than a bus service operating along dedicated corridors: Because of their high cost, the new metro systems can only be installed over a limited area and they have neither the same capacity as BRTs to satisfy all the demand, nor enough flexibility to be able to adapt to an expanding and fluctuating urban structure.
The experience of Bogota and Curitiba show that BRTs were able to maintain, or even increase, the share of public transport versus cars. Its infrastructure is relatively lightweight so that the total cost of investment is reduced by as much as a factor of compared to a heavy rail metro system.
As a consequence, for an equivalent investment, the BRT can serve up to times the urban area covered by a metro. Wright and Fjellstrom, But in poor countries, low salaries mean that other components far outweigh labour costs. Bogota built its BRT in the space of 18 months. Elevated or underground metro systems, may take more than three years to build. This time element plays an important role in political terms: An important factor, which determines the capacity of an MRT system, is the technology involved in procedures for passengers to board, alight and pay their fares.
BRTs provide quality service — which means that they are attractive to car owners for whom this point is critical — at an affordable price for the needy, without compromising the profitability of the whole operation. All of this being on offer over a large urban area, so that the less prosperous, living in the suburbs and very dependent on public transport, can still work in the city and enjoy the services it offers.
Although in theory, the most energy-saving MRT is rail transport, load-factor is also a decisive factor. Furthermore, emission also obviously depends on the energy source used to produce electricity. Non-motorised travel must not be left out 82In most cities of the South, walking and cycling are still largely prominent in the modal distribution of travel. And yet, they are more often than not ignored in the city planning process.
Mechanics: Work, Energy and Power
For example, in Bogota, where bicycles were practically extinct, the local authorities built, in just a few years, km of bicycle lanes, i. The modal share of bicycles grew from 0. A consensus was therefore formed to the effect that traditional town planning, European style, based on detailed prior planning, massive public intervention in housing and special funding for construction, was gone for ever — "the fall of the Gods" Haeringer and Goudiard, Because of general economic circumstances re-definition of frontiers between States and markets on the one hand, and on the other hand, very limited public financial resources — particularly in emerging countries, so that direct intervention in housing is a problem, with the price of real estate on the increase or even subject to speculative bubbles in many "global cities" — the "god-like" town planning era is giving way to "anticipation and support", of necessity more attentive to spontaneous forces.
Real estate and property markets, both formal and informal, send signals which are a reflection of urban structuring at work, and that regulators must integrate.
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The first task therefore is to gain a better understanding, in a particular city since the local context is essentialof intensifying forces — concentrations and extensions, dilution of urban forms, the effects of improving accessibility using MRTs as they create new polarities, and altogether to understand the factors which determine where households and activities settle.
In practical terms, public intervention is designed to complement the main thrust of urban production and, if possible, improve it.
These tools can be classified into three categories: This is where the situation is very different North and South. Setting up a land register immediately raises the difficult problem of defining and allocating property rights on land and real estate. In most countries of the South, such rights are very complex. Both traditional and imported systems are in use side by side, together with a wide variety of implementations and interpretations of the theoretical simplicity of Roman Law or even of Common Law.
Naturally, in such cities, there are many examples of occupation and construction with neither traditional nor modern legal justification of any kind, in particular on publicly-owned land. This is certainly true in theory. But in order to do so, land registers must be drawn up and rights defined. In practice however, according to Vincent Renard, land registers and legal systems for the implementation of urban property rights which were gradually put together over many years in rich cities and now proposed as a model by consultants in the cities of the South, are so sophisticated that setting up land registers would take more time than is available before the completion of the current rapid urban expansion phase Renard, As Joseph Comby also emphasises, creating a sophisticated land register can inhibit property development Comby, As regards the legalisation and registering of property ownership, much simpler solutions must be chosen, even at the price of some approximation which can be sorted out later.
For example, the simple "addressing" technique has been developed in a number of countries, in particular in World Bank programmes. Addressing consists in drawing up a register of urban population which starts very simply since the "root information" is just the address.
Later, as needed and depending on data collection capacities, a wide variety of data the authorities might require to formulate and implement their urban policies, can be added gradually, such as type of street or of building, surface area, water meter numbers, etc.