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Structure & Properties of Matter
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Each atom has a charged substructure consisting of a nucleus, which is made of protons and neutrons, surrounded by electrons.
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The periodic table orders elements horizontally by the number of protons in the atom's nucleus and places those with similar chemical properties in columns. The repeating patterns of this table reflect patterns of the outer electron states.
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The structure and interaction of matter at the bulk scale are determned by electrical forces within and between atoms.
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Stable forms of matter are those in which electric and magnetic field energy is minimized. A stable molecule has less energy, by an amount known as binding energy, than the same set of atoms separated; one must provide at least this energy in order to take the molecule apart.
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Attractions and repulsion between electric charges at the atomic scale explain the structure, properties, and transformations of matter, as well as the contact forces between material objects.
Chemical Reactions
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Chemical processes, their rates, and whether or not energy is stored or released can be understood in terms of the collisions of molecules and the rearrangement of atoms into new molecules with consequent changes in total binding energy that are matched by changes in kinetic energy.
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In many situations a dynamic and condition-dependent balance between a reaction and reverse reaction determines the number of all types of molecules present.
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The fact that atoms are conserved together with knowledge of chemical properties of the elements involved, can be used to describe and predict chemical reactions.
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Chemcial processes and properties of materials underlie many important biological and geophysical phenomena.
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When a system has a great number of component pieces, one may not be able to predict much about its precise future. For such systems one can often predict average but not detailed properties and behaviors.
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"Chemical Energy" is generally used to mean the energy that can be released or stored in chemical processes, and "electrical energy" may mean energy stored in a batter or energy transmitted by electric currents. Historically different units and names were used for the energy present in these different phenomena, and it took some time before the relationship between them were recognized.
Nuclear Processes
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Nuclear processes including fusion, fission, and radiactive decays of unstable nuclei, involve the changes in nuclear binding energies.
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The total number of neutrons plus protons does not change in any nuclear process.
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Strong and weak nuclear interactions determine nuclear stability and process.
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Spontaneous radioactive decays follow a characteristic exponential decay law. Nuclear lifetimes allow radiometric dating to be used to determine the age of rocks and other materials from the isotope ratios present.
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All forms of electricity generation and transportation fuels have associated economic, social, and environmental costs and benefits, both short and long term.
Forces & Motion
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Newton's second law accurately predicts changes in motion of macroscopoic objects, but it requires the revision for subatomic scales or for speeds close to the speed of light.
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Momentum is defined for a particular frame of reference; it is the mass times the velocity of the object.
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In any system, total momentum is always conserved.
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If a system interacts with objects outside itself, the total momentum of the system can change; however, any such change is balanced by changes in the momentum of the objects outside the system.
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Systems often change in predictable ways; understanding the forces that drive the transformation and cycles within a system, as well as forces imposed on the system from outside helps predict its behavior under a variety of conditions.
Interaction of Forces
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Newton's law of universal gravitation and Coulomb's law provide the mathematical models to describe and predict the effects of gravitational and electrostatic forces between distant objects.
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Forces at a distance are explained by fields permeating space that can transfer energy through space. Magnets or changing electric fields cause magnetic fields; electric changes or changing magnetic fields cause electric fields.
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Attraction and repulsion between electric charges at the atomic scale explain the structure, properties, and transformations of matter, as well as the contact forces between material object.
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The strong and weak nuclear interactions are important inside atomic nuclei, for example they determine the patterns of which nuclear isotopes are stable and what kind of decays occur for unstable ones.
Energy
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Energy is a quantitative property of a system that depends on the motion and interaction of matter and radiation within a system.
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That there is a single quantity called energy is due to the fact that a system's total energy is conserved even as, within the system energy is continually transferred from one object to another and between its various possible forms.
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At the macroscopic scale, energy manifests itself in multiple ways, such as in motion, sound, light and thermal energy. "Mechanical energy" generally refers to some combination of motion and stored energy in an operating machine.
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These relationships are better understood at the microscopic scale, at which all different manifestations of energy can be modeled as either motions of particles or energy stored in fields which mediated interactions between particles. This last concept includes radiation, a phenomenon in which energy stored in fields move across space.
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Conservation of energy means that the total change of energy in any system is always equal to the total energy transferred into or out of the system.
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Energy cannot be created or destroyed, but it can be transported from one place to another and transferred between systems.
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Mathematical expressions, which quantify how the stored energy in a system depends on its configuration and how kinetic energy depends on mass and speed, allows the concept of conservation of energy to be used to predict and describe system behavior.
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The availability of energy limits what can occur in any system.
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uncontrolled systems always evolve towards more stable states, that is a more uniform energy distribution.
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Any object or system that can degrade with no added energy is unstable. Eventually it will do so, but if energy releases throughout the transition are small, the process duration can be very long.
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The main way in which solar energy is captured and stored on Earth is through the chemical process known as photosynthesis.
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Solar cells are human-made devices that likewise capture the sun's energy and produce electrical energy.
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A variety of multistage physical and chemical processes in living organisms, particularly within their cells, account for the transport and transfer of energy needed for life functions.
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Although energy cannot be destroyed, it can be converted to less useful forms. Machines are judged as efficient or inefficient based on the amount of energy input needed to perform a particular useful task. Inefficient machines are those that produce more waste heat than while performing the task and thus require more energy input. It is therefore important to design for high efficiency as to reduce cost, waste materials, and may environmental impacts.
Forces & Energy
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Force fields contain energy and can transmit energy across space from one object to another.
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When two objects interacting through a force field change relative position, the energy stored in the force field is changed.
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Each force between the two interacting objects acts in the direction such that motion in that direction would reduce the energy in the force field between the objects. However, prior motion and other forces also affect the actual direction of motion.
Waves
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The wavelength and frequency of a wave are related to one another by the speed of travel of the wave, which depends on the type of wave and the medium through which it is passing. The reflection, refraction, and transmission of waves at an interface between two media can be modeled on the basis of these properties.
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Combining waves of different frequencies can make a wide variety of patterns and thereby encode and transmit information.
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Resonance is a phenomenon in which waves add up phases in a structure, growing in amplitude due to energy input near the natural vibration frequency. Strucutres have particular frequencies at which they resonate this phenomenon is used in speech and design of all musical instruments.
Electromagnetic Radiation
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Information can be digitized in this form, it can be stored reliably in computer memory and sent over long distances as a series of wave pulses.
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Electromagnetic radiation can be modeled as a wave of changing electric and magnetic fields or as a particle called a photons.
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Because a wave is not much disturbed by objects that are small compared with its wavelength, visible light cannot be used to see such objects as individual atoms.
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All electromagnetic radiation travels through a vacuum at the same speed, called the speed of light. Its speed in any other given medium depends on its wavelength and properties of the medium
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When light or longer wavelength electromagnetic radiation is absorbed in matter, it is generally converted into thermal energy.
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Shorter wavelength electromagnetic radiation can ionize atoms and cause damage to living cells.
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Photovoltaic materials emit electrons when they absorb light of a high-enough frequency.
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Atoms of each element emit and absorb characteristic frequencies of light, and nuclear transitions have distinct gama ray wavelengths. These characteristics allow identification of the presence of an element even in microscopic quantities.
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Multiple techologies based on the understanding of waves and their interactions with matter are part of everyday experiences in the modern world and in scientific research.
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Knowledge of quantum physics enabled the development of semiconductors, computer chips and lasers, all of which are now essential components of modern imaging, communication, and information technology.
