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Electric Potential and Voltage

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Overview

Energy is a notion central to physics, chemistry, physiology, and life itself. Neither life nor motion is possible without energy. In physics it is defined as the property of objects or fields, which allows it to perform work on other objects, for example to cause motion. The SI unit for energy is a joule. One joule represents the amount of energy expended while applying a force of 1 newton to a body and moving it for one meter.

Energy in Physics

Kinetic versus Potential Energy

Kinetic energy of a body with mass m moving with the speed v is equal to the work that a force needs to complete in order to accelerate the body from its rest state to the speed v. Here, work is defined as the amount of force needed to move the body over the distance s. In other words it is the energy of a moving body. Potential energy, on the other hand, is the energy of a body at rest. It is the energy needed to keep the body in the current position in space.

For example, when a tennis ball is hit by a racket and stops momentarily, the forces acting upon it (like gravity and the resistance of the racket), make it stay still in that position. At that moment it has potential energy, but not kinetic. Once it bounces off the racket and is moving away, it has kinetic energy. When the body is in motion, it has both potential and kinetic energy, and kinetic energy converts to the potential one or vice versa. For example, when a stone is thrown directly up, as it flies and slows down, kinetic energy is converted to potential. Eventually the potential energy peaks when the stone stops flying up. The stone then falls down, and as it accelerates, kinetic energy increases, while the potential energy decreases. Eventually kinetic energy reaches the maximum at the moment of impact with the Earth, when the stone stops moving.

The law of energy conservation states that the total amount of energy in an isolated system stays constant. The stone in the example above has the changing amounts of potential and kinetic energy throughout its fall, but the sum of the two is constant, because kinetic energy converts to potential energy, and vice versa.

Generating Energy

Potential and kinetic energy can be used to perform work, such as putting objects in motion. Humans have used this principle to accomplish numerous difficult tasks with the help of various devices and machines. For example, the kinetic energy of moving water was used for many centuries to move water mills that produce flour. As more and more people use technology like cars and computers in everyday life, the demand for energy is constantly increasing. Currently, the primary sources of energy are non-renewable. This means that they are from fuels mined from the Earth, and their source is not being replaced at a speed fast enough to meet the oncoming demand. Examples of such fuels are coal, oil, and uranium, used to produce nuclear energy. In recent years renewable energy, or energy from sources that can be renewed by human technology, is on the agenda of most governments and many international organizations such as the UN. A large number of research projects is focused on finding renewable energy. Some of the currently used renewable energy technologies generate wind, solar, and wave energy, among others.

Energy generated for industrial and home use is generally converted into electric energy. Electric power is the speed of energy transfer within the electric circuit. Electric power is generated by batteries or electric generators. The first power plants generated electricity from coal and hydroelectric power, but eventually other sources appeared, such as petroleum, natural gas, solar, and wind energy sources. The main principle behind power generation is to convert energy to the kind easy to transport and to use (mostly electricity). Occasionally large industrial facilities generate their own energy, but more commonly energy production is generally done in power stations on the industrial scale, because it is not logistically or economically feasible to do that in every household. This is especially true for generation of power that heavily relies on expensive technology, or technology that requires constant monitoring and safety measures, such as nuclear, wave, or wind power. One of the reasons that electric energy was chosen as the primary energy source for households and the industry is that it is easy to transport over long distances using power lines, and the losses are minimal.

Electricity can be generated from mechanical, thermal, and other forms of energy. Mechanical power includes energy generated by turbines that are moved by water, steam, hot gas, or air. Steam is created by burning fossil fuels or from nuclear reactions. Fossil fuels are fuels excavated from the earth, such as petroleum, natural gas, or coal. Because their sources are limited, they are called non-renewable sources. Renewable sources include solar, ocean, geothermal energy, and biomass.

In areas where due to infrastructure and economic problems power supply is not constant or it is not possible to access the grid, backup or portable systems are used. Many individuals, businesses, and organizations, such as hospitals, use small generators to produce electricity. These are usually reciprocating engines, which burn fossil fuels and convert the pressure generated into mechanical motion. Some areas with plentiful sunshine also use photovoltaic panels as backup.

Power Generated by Burning Fossil Fuels

Fossil fuels have formed over millions of years from the remains of plants and animals, under conditions of extreme pressure and heat within the Earth’s crust. They are usually high in carbon. These fuels release energy when burned, but they also release carbon dioxide (CO₂), one of the greenhouse gases. At the moment, fossil fuels are the major source of energy for power generation across the globe. However, greenhouse gas emissions, which they cause, contribute to global warming. An additional problem with fossil fuels is that they are not renewable and are being depleted faster than the new fossil fuels are being created. If we mostly rely on fossil fuels, we will one day run out of energy sources.

Nuclear Energy

Nuclear energy is one alternative to fossil fuels. It is generated through a controlled nuclear fission reaction,where a nucleus of an atom splits into smaller parts and releases energy. The energy heats water and produces steam, which, in turn, moves the turbines.

It poses safety concerns, especially after a number of nuclear power plant accidents, the most infamous and disastrous being the Chernobyl one in Ukraine, Three Mile Island one in the USA, and the f*ckushima one in Japan. After the f*ckushima disaster, a number of countries started to re-evaluate their use of nuclear power, and some, such as Germany, are now working on closing down their nuclear power plants in the near future.

An additional problem is the storage of spent nuclear fuel. Fuel is needed for the fission reaction to occur, and it can be reused, but eventually it has to be replaced. Some of the byproducts of nuclear power production can be reused in other industries such as medicine or weapon production, but most of the material has to be stored as radioactive waste. Currently each country has their own storage systems for the spent fuel. They include repositories in geological structures or the ocean floor, as well as storage in spent fuel pools or casks. This poses problems and risks such as costs, leakage, running out of storage, and hostile attacks on the storage facilities.

A safer alternative that is currently being researched is to produce power from nuclear fusion, a reaction that releases energy when several nuclei collide at high speed and join into a new nucleus. This happens because when two nuclei are at a very close proximity to each other, the forces that repel the nuclei are weaker than the forces that attract them together. 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.

Renewable Energy

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

Solar energy experiments started in 1873, 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 1980s. 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

Wind energy has been used by humans for a long time. The first major use was in sailing, as far as 7000 years ago. Windmills have also been in use for hundreds of years. The first wind turbines were created in the 1970s.

Marine Energy

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. Currently, wave farms exist in Portugal, the UK, Australia, and the USA, but some of them are in the experimental stages. Marine energy has a great potential to provide energy for large populations.

Biomass Energy

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.

Geothermal Energy

The Earth stores energy in its core in the form of heat. Earth’s crust has been hot since its original formation, and additional heat is constantly generated from radioactive decay of minerals. 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

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 1.2 million people have been displaced, and industrial areas as well as cities have been flooded. 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 2011 the Chinese government has acknowledged some of the problems with this project, including the increased frequency of earthquakes.

Energy in Nutrition and Exercise

Calories in Nutrition

Energy in nutrition and exercise is usually measured in kilojoules or food calories. One food calorie is equivalent to one kilocalorie or 1000 calories in the scientific notation. This is about 4.2 kilojoules. 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 1000 calories per day. The daily needs are calculated using formulas that are based on a person with average metabolism. The body’s strategies for storing and using energy are not linear, and eating fewer calories than expending may not immediately result in weight loss if the body adjusts to calorie deficiency by slowing down metabolism and needing less energy. 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 504 calories in 100 grams of chocolate (just a little less than half a cup), which is about the same as in 320 grams (1.5 cups) of cooked lean skinless white meat of turkey, or about 63 cups (about 6.3 kg) of cucumbers. 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 6.3 cups of cucumbers. 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.

Calories in Exercise

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. The excess of lactic acid results in pain, and if the activity is continued disregarding pain, then one may even become unconscious. Aerobic exercise, in contrast, uses endurance and is more long-term, such as marathon running. It trains muscles of the heart and the respiratory system, burns fat, and improves circulation.

Energy in Weight Modification

As briefly mentioned above, generally weight loss can result from expending more calories than consuming, but it is not always the case that this process occurs, or that it can be sustained over a long period of time. The body uses a range of adaptation techniques to account for the lack of energy, including a slowdown in metabolism. This results in weight loss plateaus: no weight loss despite a continuing diet or exercise routine. In this situation it is recommended to add some variety to the eating and exercise routine, such as trying out a new sport, varying the calorie intake per day, or setting weekly calorie limits instead of daily ones.

One technique is calorie shifting — gradually increasing or decreasing the daily calorie intake for a given period of time, and then resetting it back to the original amount at the end of the period. Some diet plans also suggest varying the types of food and amounts per every meal, for example, eating a small lunch heavy on carbohydrates one day, and a big protein-heavy lunch the next day. The principle behind calorie shifting is to not follow a pattern so that the body does not know how many calories per day to expect and cannot adjust accordingly by slowing down the metabolism. It is also recommended to engage in anaerobic exercises to increase muscle mass and improve metabolism, but a variety with a randomized mix of both aerobic and anaerobic is best to keep the metabolism from slowing down.

It is important to remember that muscle mass is needed for healthy metabolism, and it may help dieters to set goals of lowering total body fat instead of losing weight. Muscle tissue weighs more than fat, so when one is engaging in muscle training, some weight gain may also occur. In this situation it is useful to monitor other body measurements such as total body fat percentage, or tape measurements for different body areas such as waist or hips.

Energy Drinks

The word “energy” is widely used in marketing products. For example, energy drinks are sold as performance-enhancing beverages. They generally contain stimulants like caffeine, sometimes herb extracts, and plenty of sugar. Stimulants increase blood flow, heart rate, blood pressure, and temperature, and produce a feeling of “high,” of being energized and capable. This happens because the increase in blood flow brings more oxygen to the brain. Energy drinks should not be consumed while exercising, because they negatively affect the electrolyte balance in the body. They often contain very high levels of stimulants and provide a brief boost period followed by a withdrawal period. Energy drinks may also have other side-effects such as nausea and vomiting, headaches, high blood pressure, irregular heart rate, and insomnia. It is better not to drink energy drinks at all. Your natural energy is enough for you. If you feel tired, just have a good rest.

References

This article was written by Kateryna Yuri

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Energy and Work Converter

Energy is understood as the ability of a physical system to do work on other physical systems. Since work is defined as a force acting through a distance, energy is always equivalent to the ability to exert pulls or pushes against the basic forces of nature, along a path of a certain length. Energy is a scalar physical quantity.

In SI, energy and work are measured in joules, but in many fields units like kilowatt-hours and kilocalories are often used. The joule (J) is equal to the energy expended or work done in applying a force of one newton through a distance of one meter (1 newton meter or N·m). By another definition, the joule is equal to the energy required to pass an electric current of one ampere through a one ohm resistor for one second. Electrical energy is measured by electricity meters. Thermal energy is measured by heat meters.

Using the Energy and Work Converter Converter

This online unit converter allows quick and accurate conversion between many units of measure, from one system to another. The Unit Conversion page provides a solution for engineers, translators, and for anyone whose activities require working with quantities measured in different units.

You can use this online converter to convert between several hundred units (including metric, British and American) in 76 categories, or several thousand pairs including acceleration, area, electrical, energy, force, length, light, mass, mass flow, density, specific volume, power, pressure, stress, temperature, time, torque, velocity, viscosity, volume and capacity, volume flow, and more.
Note: Integers (numbers without a decimal period or exponent notation) are considered accurate up to 15 digits and the maximum number of digits after the decimal point is 10.

In this calculator, E notation is used to represent numbers that are too small or too large. E notation is an alternative format of the scientific notation a · 10^x. For example: 1,103,000 = 1.103 · 10⁶ = 1.103E+6. Here E (from exponent) represents “· 10^”, that is “times ten raised to the power of”. E-notation is commonly used in calculators and by scientists, mathematicians and engineers.

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