Lesson 11: Measurement by Comparison to a Known (Standard)

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Law of Conservation of Energy

by: Michael Hamilton

The Steps to Understanding Law of Conservation of Energy:

  1. The force of energy applied (work and frequency) must match. The orientation of energy must be applied in the same direction that both systems are going. (Polarity, voltage, frequency)

  2. The energy and components must match before the transfer of energy can take place. If they do not match, the transfer of energy will not occur.

  3. The systems energy must be matched with the system.
    Example: You do not put diesel fuel in a gasoline engine, because the energy (diesel fuel) does not match the system (gasoline engine) and the system will not perform.

  4. The energy must be converted adjacent to where it is needed, so as not to lose any energy while being transferred to a less efficient system.
    Example: You would not burn coal in a furnace in Virginia (for heat) and pipe it to Tennessee to warm a building. Heat would escape during this process.

  5. Minimize the number of conversions within the system, so the loss of energy is minimized.

  6. Make sure that the source that is needed is available.

  7. To make sure that the energy is used effectively, look at the entire process as a whole.


Even though the meaning is always the same, the law of conservation of energy can be stated in many different ways. Examples are: the total energy of an isolated system remains consistent; energy can neither be created nor destroyed; in the changing from one form to another, energy is always conserved.

The conservation of energy, as stated above: The total energy of an isolated system remains constant. Thus, even though energy may be changing from one form to another, energy is not lost from the system. A system is something wrapped up within boundaries, which may be real or imaginary, and isolated means that nothing from the outside affects the system (and vice versa).

For instance, the student in a classroom might be considered a system. The student may move around in the room, but if no one left or entered, the number of students would be conserved ("law of conservation of students"). We often say that the total energy of the universe is conserved. That is, the universe is the largest isolated system we can think of, and all the energy in the universe is in some form.

Energy in a system may take on various forms (e.g. kinetic, potential, heat, light). The law of conservation of energy states that energy may neither be created nor destroyed. Therefore the sum of all the energies in the system is a constant.

The law of conservation of energy is the first law of thermodynamics. A simple statement of the first law is that energy cannot be created or destroyed but only transferred from one body to another and changed from one form to another, that is, the energy of the universe is constant.

According to the second law of thermodynamics, every spontaneous change increases the entropy of the universe. The second law does not mean that local decreases in entropy cannot take place. However, if the energy of a system decreases, the energy of the surroundings must increase more. The second law makes possible predictions of the direction of change.

The first two laws are based on observations of properties of macroscopic samples of matter such as temperature, pressure, and volume. Thermodynamics was developed in the second half of the nineteenth century and the beginning of the twentieth century and, at that time, some scientists still did not believe in atoms. Therefore, the first two laws of thermodynamics are not based on any model of the microscopic nature of matter.

The third law was not stated in its modern form until 1923 (after the atomic theory was accepted and the quantum theory had been invented). The third law of thermodynamics says that the entropy of perfect crystalline substances (those with no disorder) is zero at the absolute zero of temperature (0°K); however, it is impossible to reach absolute zero.

When a piece of copper metal is heated in air, it comes together with oxygen in the air. Then if it is weighed, it is found to have a greater mass than the original piece of metal. If, however, the mass of the oxygen of the air that combines with the metal is taken into consideration, it can be shown that the mass of the product is within the limits of accuracy of any weighing instrument, equal to the sum of the masses of the copper and oxygen that combine. This behavior of matter is in accord with what is called the Law of Conservation of Matter. During an ordinary chemical change, there is no detectable increase or decrease in the quantity of matter. Conversion of one type of matter into another is always accompanied by the conversion of one form of energy into another. Usually heat is leveled or absorbed, but sometimes the conversion involves light or electrical energy instead of, or in addition to, heat. Many transformations of energy, of course, do not involve chemical changes. Electrical energy can be changed into either mechanical, light, heat or potential energy without chemical changes. Mechanical energy is converted into electrical energy in a generator. Potential and kinetic energy can be converted into one another. Many other conversions are possible, but all of the energy involved in any change always appears in some form after the change is completed.

 

The Law of Conservation of Energy states that energy cannot be created or destroyed, but can change its form. The total quantity of matter and energy available in the universe is a fixed amount and never any more or less.

 

Energy

Energy is the ability or capacity to do work. Several forms of energy include heat, chemical energy, and, according to the theory of relativity ad mass, other forms of energy are associated with the transmission of light, sound, and electricity. Energy and work are measured in the same units: joules, ergs, electron-volts, calories, foot-pounds, or some other, depending on the system of measurement being used. When a force acts on a body, the work performed (and the energy expended) is the product of the force and the distance over which it is exerted. Potential energy is the capacity for doing work that a body possesses because of its position or condition. For example, a weight lifted to a certain height has potential energy because of its position in earth's gravitational field. Kinetic energy, the energy a body possesses because it is in motion, is equal to (1/2 mv2) where m is its mass and v is its velocity. The average kinetic energy of the atoms or molecules of a body is measured by the temperature of the body. The normal form of wasted energy is heat. Energy (or its equivalent in mass) can be neither created nor destroyed (law of conservation of matter and energy), but it can be changed from one form into another.

Law of Conservation of Energy During Transfer
  1. Right direction.
  2. Matched components.
  3. Matched to energy source.
  4. Minimized transformation.
  5. Convert as close to where it's needed as possible.