As students select and use appropriate units and instruments for measurement to achieve the degree of precision and accuracy required in real-world situations, they also understand and use the tools of data analysis for managing information. Each student describes, analyzes, and generalizes a wide variety of patterns, relations, and functions. Each student uses the scientific processes and habits of mind to solve problems. Each student understands that all matter has observable, measurable properties. Matter is made of minute particles called atoms, and atoms are composed of even smaller components. These components have measurable properties, such as mass and electrical charge. Each atom has a positively charged nucleus surrounded by negatively charged electrons. The electric force between the nucleus and electrons holds the atom together. Atoms interact with one another by transferring or sharing electrons that are furthest from the nucleus.
These outer electrons govern the chemical properties of the element. Chemical reactions may release or consume energy. Some reactions such as the burning of fossil fuels release large amounts of energy by losing heat and by emitting light. Light can initiate many chemical reactions such as photosynthesis and the evolution of urban smog. Reactions involve electron transfer. A large number of important reactions involve the transfer of either electrons (oxidation/reduction reactions) or hydrogen ions (acid/base reactions) between reacting ions, molecules, or atoms. In other reactions, chemical bonds are broken by heat or light to form very reactive radicals with electrons ready to form new bonds. Radical reactions control many processes such as the presence of ozone and greenhouse gases in the atmosphere, burning and processing of fossil fuels, the formation of polymers, and explosions. Catalysts accelerate chemical reactions. Catalysts, such as metal surfaces, accelerate chemical reactions. Chemical reactions in living systems are catalyzed by protein molecules called enzymes.
Experiments determine that the rates of reaction among atoms and molecules depend on the concentration, pressure, and temperature of the reactants and the presence of catalysts. Each Student understands that the total energy in the universe is constant. Energy can be transferred by collisions in chemical and nuclear reactions, by light waves and other radiations, and in many other ways. However, it can never be destroyed. As these transfers occur, the matter involved becomes steadily less ordered. All energy is either kinetic or potential. All energy can be considered to be either kinetic energy, which is the energy of motion, potential energy, which depends on relative position, or energy contained by a field, such as electromagnetic waves.
Energy is quantized. Each kind of atom or molecule can gain or lose energy only in particular discrete amounts and thus can absorb and emit light only at wavelengths corresponding to these amounts. These wavelengths can be used to identify the substance. Electrons flow in materials and, in some materials such as metals, electrons flow easily, whereas, in insulating materials such as glass, they can hardly flow at all. Semiconducting materials have intermediate behavior. At low temperatures, some materials become superconductors and offer no resistance to the flow of electrons. The term for the amount of energy produced by the Sun over a specific area is solar irradiation and it is usually expressed in terms of watts per square meter (Watts/m
2
). One of the ways you can measure this energy is through special instruments called pyranometers or pyrheliometers. A pyranometer measures the Sun's radiation and any extra radiation that has been scattered by particles in the sky. A pyrheliometer measures the direct Sun's radiation. In one project, you will make a pyranometer and pyrheliometer by using a solar cell. You will connect the cell to something that measures current such as a millameter or voltmeter. The first step in understanding solar irradiation begins with understanding the Sun. The Sun is a sphere of intensely hot gasses that is about 150 million kilometers from Earth.[18] The temperature on the Sun ranges from about 5,700 degrees Celsius at the surface to an estimated 14 million degrees Celsius in the center.[18]The amount of energy that reaches earth is an extremely small fraction, only about one-billionth of the energy on the Sun.[20]
