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- Absolute Pressure - A pressure at absolute zero can only exist in a total vacuum and any pressure above this is called absolute pressure.
- Amount of Substance - The quantity of a substance present, measured in terms of the number of particles (atoms, molecules, ions, etc.) that the substance contains. The unit of measurement for amount of substance in the International System of Units (SI) is the mole (mol).
- Atomic Mass - ,A measure of the average mass of the atoms in a chemical element. The atomic mass of an element takes into account the masses of the protons, neutrons, and electrons in its atoms. Protons and neutrons are found in the atomic nucleus, while electrons orbit around the nucleus. Since the mass of an electron is much smaller compared to the mass of protons and neutrons, it is often neglected when calculating atomic mass.
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- Ion - An electrical charge on an atom or group of atoms. They are either a [[cation]] (positive charge) or an anion (negative charge). Knowledge of the type of charge allows for theoretical prediction of possible compounds which can be formed by the oppositely charged ions.
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- Nuclear Energy - The energy released from the nucleus of an atom during a nuclear reaction. The energy released during a nuclear reaction is equal to the change in mass multiplied by the speed of light squared. The change in mass represents the difference between the mass of the reactants and the mass of the products. Nuclear reactions can release enormous amounts of energy, which makes nuclear energy a very powerful source of energy.
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Nuclear Reaction - A process in which the nucleus of an atom is altered, resulting in a change in the atomic number or mass of the nucleus. Nuclear reactions can be either spontaneous or induced, and can release or absorb large amounts of energy. Nuclear reactions can have both beneficial and harmful effects on the environment and human health.
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- Planck Energy - A fundamental unit of energy in the context of Planck units, which is a set of natural units that arise from combining fundamental physical constants in a way that simplifies various equations in theoretical physics.
- Planck Length - A fundamental unit of length in the system of natural units known as Planck units. It is denoted by and is derived from fundamental physical constants such as the speed of light, the gravitational constant, and the reduced Planck constant. It is thought to be the smallest possible length in a section on spacetime.
- Planck Mass - A unit of mass in the system of natural units known as Planck units. It derived from fundamental physical constants such as the speed of light, the gravitational constant, and the reduced Planck constant.
- Planck Temperature - A unit in the system of Planck units. This temperature is the highest theoretically possible temperature in the universe according to current physical theories. It is derived from fundamental constants such as the speed of light, the gravitational constant, and the reduced Planck constant.
- Planck Time - The unit of time in the system of natural units known as Planck units. It is defined as the time it would take a photon traveling at the speed of light to cross a distance equal to the Planck length. Planck time is denoted by and is calculated using fundamental constants such as the speed of light, the gravitational constant, and the reduced Planck constant.
- Planck's Law - A physical constant that relates the energy of one photon of electromagnetic waves to the frequency of that wave used in classic mechanics and quantum mechanics. Planck units are based on physical constants rather than human scales. The law states that the spectral radiance (the amount of radiation emitted per unit area, per unit solid angle, per unit frequency) of a black body at a specific wavelength and temperature is proportional to the product of the frequency of the radiation and the temperature, raised to the power of -1, and multiplied by a constant known as the Planck constant.
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