User talk:Paul Wormer/scratchbook: Difference between revisions
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'''Energy''' is a property of a system that produces action (makes things happen) or, in some cases, has the "potential" to make things happen. For example, energy can put objects into motion, it can change the temperature of objects and it can transform matter from one form to another, | '''Energy''' is a property of a system that produces action (makes things happen) or, in some cases, has the "potential" to make things happen. For example, energy can put objects into motion, it can change the temperature of objects and it can transform matter from one form to another, for instance it turns ice (solid) into water (liquid). Quantitatively, energy is a measurable physical quantity of a system that has the dimension <font style="font-family: sans-serif"> M(L/T)<sup>2</sup></font> (mass times length squared over time squared). The corresponding [[SI]] (metric) unit is [[joule]] [kg(m/s)<sup>2</sup>]; other measurement units are ergs, calories, watt-hours, Btu, etc. Energy lights our cities, powers our vehicles, and runs machinery in factories. It warms and cools our homes, cooks our food, plays our recorded music, and gives us pictures on television. It is difficult, or maybe impossible, to give an all-embracing definition of energy exactly because it exists in so many forms, such as kinetic or mechanical energy, potential energy, thermal energy or heat,<ref>Strictly speaking there is a distinction between heat and thermal energy. The distinction is that an object possesses thermal energy while heat is the transfer of thermal energy from one object to another. However, in practice, the words "heat" and "thermal energy" are often used interchangeably</ref> light, electrical energy, chemical energy, nuclear energy, etc. Indeed, it took scientists a long time to realize that the different manifestations of energy are really the same property that rightfully may carry a the same name (energy). From the middle of the 18th to the middle of 19th century scientists became to realize that the different forms of energy can be converted into each other, and moreover that no energy is lost in the conversion processes. | ||
Let us consider as a practical example of the conversion of energy a [[conventional coal-fired power plant]]. Such a plant takes as input coal ([[carbon]]) and air ([[oxygen]]). These two raw materials can combine, i.e., the coal is burned, and combustion energy, a form of heat, is generated. Combustion energy is converted into electrical energy which is transported to cities and factories through high [[voltage]] [[power]] lines. It would be vey nice, and would go a long way in solving the [[energy crisis]], if all combustion energy would be converted into electrical energy. Unfortunately, this is not the case, the laws of physics do not allow it. [[Thermodynamics]] dictates that a large (as much as 60%) amount of the combustion energy is carried off as heat by cooling water. Although the hot water produced by the electricity plant is of little practical use and sometimes a burden to the environment, it still contains (thermal) energy that (theoretically not pracically) can be used to perform work. | Let us consider as a practical example of the conversion of energy a [[conventional coal-fired power plant]]. Such a plant takes as input coal ([[carbon]]) and air ([[oxygen]]). These two raw materials can combine, i.e., the coal is burned, and combustion energy, a form of heat, is generated. Combustion energy is converted into electrical energy which is transported to cities and factories through high [[voltage]] [[power]] lines. It would be vey nice, and would go a long way in solving the [[energy crisis]], if all combustion energy would be converted into electrical energy. Unfortunately, this is not the case, the laws of physics do not allow it. [[Thermodynamics]] dictates that a large (as much as 60%) amount of the combustion energy is carried off as heat by cooling water. Although the hot water produced by the electricity plant is of little practical use and sometimes a burden to the environment, it still contains (thermal) energy that (theoretically not pracically) can be used to perform work. | ||
Revision as of 14:57, 6 March 2009
Energy is a property of a system that produces action (makes things happen) or, in some cases, has the "potential" to make things happen. For example, energy can put objects into motion, it can change the temperature of objects and it can transform matter from one form to another, for instance it turns ice (solid) into water (liquid). Quantitatively, energy is a measurable physical quantity of a system that has the dimension M(L/T)2 (mass times length squared over time squared). The corresponding SI (metric) unit is joule [kg(m/s)2]; other measurement units are ergs, calories, watt-hours, Btu, etc. Energy lights our cities, powers our vehicles, and runs machinery in factories. It warms and cools our homes, cooks our food, plays our recorded music, and gives us pictures on television. It is difficult, or maybe impossible, to give an all-embracing definition of energy exactly because it exists in so many forms, such as kinetic or mechanical energy, potential energy, thermal energy or heat,[1] light, electrical energy, chemical energy, nuclear energy, etc. Indeed, it took scientists a long time to realize that the different manifestations of energy are really the same property that rightfully may carry a the same name (energy). From the middle of the 18th to the middle of 19th century scientists became to realize that the different forms of energy can be converted into each other, and moreover that no energy is lost in the conversion processes.
Let us consider as a practical example of the conversion of energy a conventional coal-fired power plant. Such a plant takes as input coal (carbon) and air (oxygen). These two raw materials can combine, i.e., the coal is burned, and combustion energy, a form of heat, is generated. Combustion energy is converted into electrical energy which is transported to cities and factories through high voltage power lines. It would be vey nice, and would go a long way in solving the energy crisis, if all combustion energy would be converted into electrical energy. Unfortunately, this is not the case, the laws of physics do not allow it. Thermodynamics dictates that a large (as much as 60%) amount of the combustion energy is carried off as heat by cooling water. Although the hot water produced by the electricity plant is of little practical use and sometimes a burden to the environment, it still contains (thermal) energy that (theoretically not pracically) can be used to perform work.
- ↑ Strictly speaking there is a distinction between heat and thermal energy. The distinction is that an object possesses thermal energy while heat is the transfer of thermal energy from one object to another. However, in practice, the words "heat" and "thermal energy" are often used interchangeably