Energy (physics)
Energy, in the realm of physics, is a fundamental property of matter that embodies the capacity of a physical system to do work or induce change. It exists in various forms, such as kinetic energy, which is the energy of motion, and potential energy, which is stored energy based on an object's position or configuration. The principle of energy conservation states that energy cannot be created or destroyed, only transformed from one form to another. For instance, in a swinging pendulum, potential energy is maximized at the extremes of the swing and converts to kinetic energy as it moves through the center, demonstrating the interplay between these two energy forms.
Energy can also manifest as thermal energy, which relates to the temperature and motion of particles within a substance. Other notable forms include elastic energy, electrical energy, and chemical energy, each relevant in various physical contexts. The transfer of energy plays a critical role in enabling work, described in physics as the movement of an object caused by a force. In everyday scenarios, energy conversion can be observed in activities like playing billiards or using springs, where energy is transferred and transformed, illustrating the dynamic nature of energy in our world. Understanding energy is not only essential for grasping physical principles but is also vital for various applications in technology and the sustenance of life itself.
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Energy (physics)
In physics, energy is a property of matter. Broadly speaking, the term "energy" refers to the capacity of a physical system to do work or to otherwise bring about a change in the system. Energy may not always be available to do work, but the potential always exists for it to be converted into a form that is able to do so.
Energy has a few important properties. For one, energy cannot be created or destroyed, only converted from one form to another. This property is defined by the law of conservation of energy.
Background
Energy comes in a variety of different forms, including mechanical energy (made up of kinetic and potential energy), elastic energy, and thermal energy. While energy can change forms, the law of conservation of energy states that it cannot be created or destroyed.
The process of energy conversion can be illustrated with a common example involving potential and kinetic energy. Think of the pendulum of a clock. At the extremes of each swing, the pendulum is momentarily still as it changes direction. In that moment, its potential energy is at a maximum and its kinetic energy is at a minimum, because it is at its maximum attainable height and it is not moving. When the pendulum starts to move again, its potential energy is converted into kinetic energy so that in the middle of its swing, when its speed is the greatest, the pendulum’s kinetic energy is at a maximum and its potential energy is at a minimum. Once the pendulum passes the midpoint, it starts to slow again as it approaches the opposite extreme of its swing, and the kinetic energy is once again converted to potential energy. This process repeats until the pendulum stops swinging.
Energy is related to work in the sense that work, as it is understood in physics, describes the transfer of energy from one system to another. When a force acts on a body to make it move, work is said to have been done. The amount of work done is equal to the magnitude of the force applied to the body multiplied by the distance the body moves in the direction of the applied force.
Overview
Kinetic energy is the energy an object possesses as a result of its motion. It is a product of the mass of the object and the velocity at which it is traveling. The amount of kinetic energy possessed by a given object is equal to the amount of work required to accelerate it to its current velocity. One object can transfer kinetic energy to another by exerting force to do work on it. Consider a billiards table. When a person uses a billiards cue to strike the white cue ball, they are doing work by applying force to the ball and causing it to move, thus transferring kinetic energy from the cue (and the person holding it) to the ball. If the cue ball strikes another ball, the kinetic energy will transfer from the cue ball to the second ball, causing the second ball to move while the cue ball comes to a halt.
Potential energy is most commonly discussed in relation to kinetic energy, but there are a number of different forms of potential energy, including gravitational potential energy, electric potential energy, and chemical potential energy. Potential energy is simply the energy an object possesses due to its position relative to other objects or to a force field. The potential energy described in the pendulum example above is gravitational potential energy, a type of mechanical potential energy, because it is Earth’s gravitational field (assuming that the pendulum is on Earth) that causes the pendulum to fall back down from each extreme of its swing. Similarly, electric potential energy is the potential energy that an electric charge possesses due to its position relative to an electric field, and chemical potential energy is the potential energy that atoms or molecules possess due to their arrangement relative to other atoms or molecules, or the arrangement of particles within the atom or molecule.
Elastic energy is another form of potential energy. Another way to think of potential energy is as the difference in energy between an object’s current position and a given reference position, a concept that can easily be illustrated by the elastic energy of a spring. If an object is attached to a spring, the reference position of that object, in which it has zero potential energy, is its position when the spring is in its natural, unextended or uncompressed state. If the spring is displaced from its reference point by extension or compression, it will exert a force that is proportional to the amount of displacement so that, when it is released, it will return to its reference position. This type of force, known as a restoring force, is characteristic of elastic materials. While the spring is being extended or compressed, the object attached to it has elastic potential energy; when the spring is released, the elastic potential energy is converted into kinetic energy as the object returns with the spring to the reference position.
Thermal energy is the internal energy contained in a system due to its temperature. According to the kinetic theory of matter, the thermal energy of an object or system is the sum of the kinetic energies of all of its component particles, while the temperature of that object or system is the average kinetic energy per particle. All matter particles are constantly moving; the higher the temperature of the matter, the faster the particles move and the greater their kinetic energy—and, thus, the greater the thermal energy of the matter made up of those particles. Consider particles in a gas. At any given moment, some of the gas particles will be moving faster than others, but the particles are constantly colliding with each other, resulting in the transfer of kinetic energy as one particle speeds up and the other slows down. As a result, the overall kinetic energy of the gas particles—both the sum and the average—remains constant. However, if thermal energy is added to the gas, the average kinetic energy of the gas particles, and thus the temperature of the gas, will also increase. One might think of this as adding heat to the gas, but heat, in the context of physics, is not itself a form of energy; rather, it refers to the transfer of thermal energy from one system to another, much like work is the transfer of mechanical energy.
These are just a few of the many different forms that energy can take. Other forms include electric energy, chemical energy, electromagnetic or radiant energy, and nuclear energy, among many others. Whatever its form, energy is essential not just to civilization but to the existence of life itself.
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