Similar to nuclear fission, this reaction produces radioactive waste, but this waste will cease to be radioactive after about one hundred years, compared to thousands of years with nuclear fission. The materials needed to produce this reaction are also less costly.
At the moment, fusion reactions require high amounts of energy to facilitate, but researchers are working on ways to make this reaction produce more energy than it requires and make it economical.
Other alternatives include using renewable power sources, such as energy from waves, sunlight, and wind. At the moment these alternative sources are not developed enough to replace fossil fuels. However, thanks to the subsidies provided by some governments, and also because these energy sources are much less harmful to the environment than the non-renewable ones, they are becoming more and more popular.
Solar energy experiments started in , but this technology was not widely used until recently. In recent years, solar industry is developing very rapidly due to demand and subsidies from governments and international organizations. Solar farms, which are large areas covered with solar panels, were first built in the s. Most often solar energy is collected and electricity is generated by means of photovoltaic panels.
Sometimes heat engines are used in which solar energy heats water and resulting water vapour rotates the turbines, which in turn rotate generators. Wind energy has been used by humans for a long time. The first major use was in sailing, as far as years ago. Windmills have also been in use for hundreds of years. The first wind turbines were created in the s. Tidal energy has also been used since the time of the Roman Empire, but the energy of waves and currents has only been used recently.
In recent years stations that harvest wave, tidal, and current energy are being built and tested. While the idea of generating energy from marine power is not new, devices that harvest this energy on a large scale need to be further developed and tested. This is mainly due to high costs of building such power stations, and to the lack of advancement in current technologies.
Marine energy has a great potential to provide energy for large populations. Biomass or biofuel generates energy when plant material is burned. During this process solar energy that plants generated through photosynthesis is released as heat.
It is widely used in everyday life, for example to provide warmth for heating and cooking, and also as fuel for transportation. Alcohols and oils can be made from plants, and animal fat-based biofuel is also in use. One variation of biofuel, biodiesel, is used in the automotive industry both as an additive to other diesel fuels, or by itself. The Earth stores energy in its core in the form of heat. Until recently, this energy has been accessible mostly in the areas that lie around the borders of tectonic plates, where hot springs are present.
Now, geothermal wells are created to have access to this energy more widely. This is a costly process, however. Hydroelectric energy is another alternative to fossil fuels. Hydro generated power is considered by many to be clean energy with little negative environmental impact. Indeed, with this energy source greenhouse gas emissions are not a problem as they are for fossil fuels.
Hydroelectric energy is generated by water flow. It has been in use by humans for a long time. A watermill is one example of using this energy. Currently, electricity is generated by harvesting kinetic energy of flowing water of rivers, or potential energy of water in reservoirs.
This energy moves water turbines. The dams use the height difference between the reservoir from which the water flows, and the river into which the water flows. Despite the positive aspects of hydroelectric energy, numerous problems exist with its generation.
For example, displacing and damaging habitats when building dams causes considerable harm to the biodiversity. As a result of building dams plants and animals become cut off from the resources, normally available in their ecosystem. For example, fish may not be able to go upstream to lay eggs, and may be unable to adjust to the new environment. Displacement of people due to dam construction is a humanitarian issue in some countries where construction is not regulated by the public and the government.
One of the most notorious dam projects known for human rights violations and environmental problems is the Three Gorges Dam project in China. While building this dam, over 1. This is a problem because human and industrial waste on the flooded territory polluted the water. Scientists worry that creating a reservoir of this scale threatens increased landslides this is already a problem and potential for earthquakes.
Since the Chinese government has acknowledged some of the problems with this project, including the increased frequency of earthquakes.
Energy in nutrition and exercise is usually measured in kilojoules or food calories. One food calorie is equivalent to one kilocalorie or calories in the scientific notation. This is about 4. One food calorie is formally defined as the amount of energy needed to raise the temperature of one kilogram of water by one degree in the Kelvin scale.
There are 9 food calories, or simply calories per gram in fats, 4 calories per gram in carbohydrates and proteins, and 7 calories per gram in alcohols.
Some other substances also contain calories. This energy is released during metabolism. When dieting, people often calculate calories consumed through food and drink, and expended through exercise to determine whether they eat more or less than their daily calorie needs. The idea behind calorie counting is to eat fewer calories than the daily need, although most dietitians and doctors recommend that it is dangerous to regularly eat fewer than calories per day.
The daily needs are calculated using formulas that are based on a person with average metabolism. Nonetheless, most sources for healthy nutrition and exercise recommend tracking the daily calorie intake. Calorie density or energy density is a useful concept in nutrition.
It refers to the amount of calories per gram of food. Foods low in calorie density often have a high water content. They fill the stomach and give the feeling of fullness with fewer calories than a food high in calorie density would. For example, there are calories in grams of chocolate just a little less than half a cup , which is about the same as in grams 1. Perhaps, it is easier to imagine that one chocolate candy contains about the same amount of calories 50 as a little over a table spoon of turkey, or 6.
If one compares the feeling of fullness after eating 6 cups of cucumbers and one chocolate candy, it is very likely that eating the cucumbers will make the eater feel full, while the chocolate, on the other hand, fuels a desire to eat more. Knowing the calorie density of foods is, therefore, very useful for people who are trying to eat fewer calories.
However, while it is true that most unhealthy foods are high in fat and sugar and are also high in calorie density, anyone on a path to healthy living has to consider not only the calorie content of foods but their nutritional value as well. Nutrient density is a similar concept; it compares the amount of nutritious elements such as vitamins, dietary fiber, antioxidants, and minerals, to the amount of energy in a given food.
Thus, foods high in nutrient density are foods that have a high amount of nutrients per a given unit of energy. The opposite are the empty calorie foods that have little or no nutrition value. Alcohol is one example of such foods. Individuals should minimize consumption of empty calorie foods, especially if they are dieting, because they may not get enough nutrition. Energy used by the human body is needed to maintain the basal metabolic rate BMR , which constitutes the amount of energy needed to support a living body at rest.
This includes supporting the metabolism of the brain, as well as of the other organs and tissues. It is also used to support physical activity. The BMR, and by extension the total energy expended increase as the body looses fat and gains muscle tissue.
Both losing fat and gaining muscle help improve the metabolism and the overall health of the body, therefore it is generally recommended to combine healthy eating with exercise that maintains and develops muscles. The effect of exercise on the energy expended by the body depends on whether the exercise is aerobic or anaerobic.
Aerobic exercise uses oxygen to break down glucose and generate energy, while anaerobic exercise uses phosphocreatine instead to produce the energy needed for the exercise. Anaerobic exercise helps increase the muscle mass. It is more intense and short-term, such as sprinting and lifting weights. It cannot be done for long periods of time because lactic acid enters the bloodstream as a byproduct of the chemical reaction needed to produce energy.
Thus the simpler notation for nuclides is A X, which is sufficient and is most commonly used. We read this backward, saying helium-4 for 4 He, or uranium for U. A variety of experiments indicate that a nucleus behaves something like a tightly packed ball of nucleons, as illustrated in Figure 2. These nucleons have large kinetic energies and, thus, move rapidly in very close contact.
Nucleons can be separated by a large force, such as in a collision with another nucleus, but resist strongly being pushed closer together. This is what would happen if you pack nucleons so closely that there is no empty space between them. Nucleons are held together by nuclear forces and resist both being pulled apart and pushed inside one another.
The volume of the nucleus is the sum of the volumes of the nucleons in it, here shown in different colors to represent protons and neutrons. Substituting the values for r 0 and A yields. The radius of this medium-sized nucleus is found to be approximately 4. The density found here is so large as to cause disbelief. It is consistent with earlier discussions we have had about the nucleus being very small and containing nearly all of the mass of the atom.
One cubic meter of nuclear matter, such as found in a neutron star, has the same mass as a cube of water 61 km on a side. What forces hold a nucleus together? The nucleus is very small and its protons, being positive, exert tremendous repulsive forces on one another. The answer is that two previously unknown forces hold the nucleus together and make it into a tightly packed ball of nucleons. These forces are called the weak and strong nuclear forces. Nuclear forces are so short ranged that they fall to zero strength when nucleons are separated by only a few fm.
However, like glue, they are strongly attracted when the nucleons get close to one another. The strong nuclear force is about times more attractive than the repulsive EM force, easily holding the nucleons together. Nuclear forces become extremely repulsive if the nucleons get too close, making nucleons strongly resist being pushed inside one another, something like ball bearings. The fact that nuclear forces are very strong is responsible for the very large energies emitted in nuclear decay.
The many stable and unstable nuclei we have explored, and the hundreds we have not discussed, can be arranged in a table called the chart of the nuclides , a simplified version of which is shown in Figure 3. Nuclides are located on a plot of N versus Z. Examination of a detailed chart of the nuclides reveals patterns in the characteristics of nuclei, such as stability, abundance, and types of decay, analogous to but more complex than the systematics in the periodic table of the elements.
Figure 3. Simplified chart of the nuclides, a graph of N versus Z for known nuclides. The patterns of stable and unstable nuclides reveal characteristics of the nuclear forces. Numbers along diagonals are mass numbers A. Figure 4. Jensen for the creation of the nuclear shell model. This successful nuclear model has nucleons filling shells analogous to electron shells in atoms. It was inspired by patterns observed in nuclear properties. In principle, a nucleus can have any combination of protons and neutrons, but Figure 3 shows a definite pattern for those that are stable.
For low-mass nuclei, there is a strong tendency for N and Z to be nearly equal. More detailed examination reveals greater stability when N and Z are even numbers—nuclear forces are more attractive when neutrons and protons are in pairs. For increasingly higher masses, there are progressively more neutrons than protons in stable nuclei.
The mass of a proton is 1. The combined mass is calculated: 29 protons 1. Example: Determine the binding energy of the copper atom.
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