NATS From the Cosmos to Earth Law of Conservation of Energy Energy can be neither created nor destroyed. It merely changes it form or is exchanged between objects. This principle (or law) is fundamental to science. The total energy content of the Universe was determined in the Big Bang and remains the same today.

NATS From the Cosmos to Earth Conversion of Energy Throwing a baseball Nuclear energy (nuclear fusion on sun) - Radiative energy (sunlight) - Chemical energy (photosynthesis) - Chemical energy in pitcher’s body (from eating plants) - Mechanical kinetic energy (motion of arm) - Mechanical kinetic energy (movement of the baseball). Thus, ultimate source of KE in baseball is mass energy stored in hydrogen of Sun - created in Big Bang. Hydroelectric dam Gravitational - mechanical - electrical Nuclear reactor Nuclear - thermal - mechanical - electrical Car Chemical - thermal - mechanical

NATS From the Cosmos to Earth Temperature and Thermal Energy Why does water burn your skin so much quicker than air? Why is falling into a 32º F lake more dangerous than standing outside naked on a 32º F? Temperature - measure of the average kinetic energy of the particles in a substance - particles in box on right have higher temperature - higher velocity = more KE = higher temperature Both boxes have same temperature - particles have same average velocity/KE - box on right has more thermal energy - energy contained in a substance - more particles

NATS From the Cosmos to Earth This diagram compares three common temperature scales. The Fahrenheit scale is used in the United States, but nearly all other countries use the Celsius scale. Scientists prefer the Kelvin scale because O K represents absolute zero, the coldest possible temperature.

NATS From the Cosmos to Earth Conversion Between Celsius and Fahrenheit ºF = ºC x 9/5 + 32º ºC = (ºF - 32) x 5/9

NATS From the Cosmos to Earth STATES OF MATTER: Gas — fixed quantity Liquid— fixed quantity and size, shape conforms to container Solid— fixed quantity, size and shape

NATS From the Cosmos to Earth The state of matter is determined by its temperature. Consider water: Below 32º F - ice - relatively low KE - each molecule tightly bound to it neighbors - solid At 32º F molecules have enough energy to break solid bonds of ice - remain together but move relatively freely - liquid At 212º F water boils and turns to gas - molecules break free of all bonds with neighbors - move independently of other molecules - gas

NATS From the Cosmos to Earth Size VirusSmallest Living Thing10 millionth of 1 cm cm Molecule1/100 of a Virus10 -7 cm Atom 1 1/10 of a Molecule10 -8 cm Nucleus1/100,000 of an Atom cm Proton Neutron 1/10 of a Nucleus cm QuarkMuch smaller than a Proton ??? 1 size of atom = 1 cm 1 cm 1000 km 1000 km = 600 miles, the distance from Dallas to El Paso Structure of Matter

NATS From the Cosmos to Earth Atom nucleus electrons e-e- protons neutrons p+p+ n Atom - comes from Greek word for “indivisible”. Named by Democritus (c B.C.) - believed that if a piece of matter, e.g., a rock, could be broken into pieces small enough that nothing smaller could be possible.

NATS From the Cosmos to Earth Charge Electrical charge is a fundamental physical property that is always conserved - like energy. The proton is positively charged - 1 positive basic unit of charge. The electron is charged negatively - 1 negative basic unit of charge. The neutron is neutral. Like charges repel and unlike charges attract - electromagnetic force. Electron bound to atom by electromagnetic bonding - positive charge of nucleus - negative charge of electrons. In natural state - equal number of electrons and protons - atom has neutral charge. Nucleus bound by strong nuclear force - stronger than repellent electromagnetic force of protons that tries to break nucleus apart.

NATS From the Cosmos to Earth The “size” of an Atom Although it is the smallest part of the atom, most of the atom’s mass is contained in the nucleus. The electrons do not “orbit” the nucleus; they are “smeared out” in a cloud which give the atom its size. Solids made up of almost completely empty space - solidity comes from electric interactions between charged particles in its atoms and the strange quantum laws governing electron behavior. One drop of water contains atoms - more than stars in the universe

NATS From the Cosmos to Earth Hydrogen e-e- p+p+ 1 electron 1 proton 0 neutrons

NATS From the Cosmos to Earth Helium e-e- p+p+ n e-e- n p+p+ 2 electrons 2 protons 2 neutrons

NATS From the Cosmos to Earth Hydrogen e-e- p+p+ n Deuterium isotope 1 electron 1 proton 1 neutron An isotope of an element has the same number of protons but a different number of neutrons.

NATS From the Cosmos to Earth The particles in the nucleus determine the element and isotope. = == = = = = = +++ +

NATS From the Cosmos to Earth Periodic Table of the Elements 118 known elements as of occur naturally. Only 111 officially recognized and named. The first man-made element was Technetium in All man-made elements radioactive with short half-lives so that any that were present at the formation of Earth have long since decayed.

NATS From the Cosmos to Earth The periodic table groups elements with similar chemical properties together - largely driven by electron structure of elements. Electrons exist on shells - each shell has a maximum allowable number of electrons. Many chemical properties dependent on number of electrons in outer shell.

NATS From the Cosmos to Earth p+p+ n e-e- n p+p+ atomic number = 2 atomic mass number = 4 What if an Electron is Missing? The atom becomes an ion with a positive charge. He +1

NATS From the Cosmos to Earth Plasma- 4th State of Matter Temperature so high that atoms are ionized - negatively charged free electrons move among positively charged ions - motions controlled by electromagnetic forces (repulsion/attraction) instead of collisions.

NATS From the Cosmos to Earth What if two or more atoms combine to form a particle? p+p+ p+p+ 8p + 8n molecule H 2 O (water)

NATS From the Cosmos to Earth Electron Orbits Electrons can gain or lose energy while they orbit the nucleus - this energy is the electric potential energy - as opposed to the other two energies an atom has - mass energy and kinetic energy. When electrons have the lowest energy possible, we say the atom is in the ground state. When electrons have more energy than this, we say the atom is in an excited state. When electrons gain enough energy to escape the nucleus, the atom is ionized.

NATS From the Cosmos to Earth Electron Energy Levels Electrons can not have just any energy while orbiting the nucleus. Only certain energy values are allowed. Electrons may only gain or lose certain specific amounts of energy. Each element (atom and ion) has its own distinctive set or pattern of energy levels - holds the key to studying of distant objects in the universe. This diagram depicts the energy levels of Hydrogen. 1 eV (electron volt) = 1.6 X J Electron jumps to higher energy levels can only occur with addition of the particular amounts of energy representing differences between possible energy levels. Energy levels are quantized - study of electron energy levels called quantum mechanics. Atom gains this energy either from KE of another atom colliding with it or from absorption of energy carried by light - falls to lower energy level by emitting light or transfer of energy by collision.

NATS From the Cosmos to Earth Nuclear Fission Neutron strikes nucleus - breaks it apart into two separate atoms - different elements - releases another two neutrons + energy - if enough material is present (critical mass) - run away reaction leads to explosion - atomic bomb. Controlled reaction - nuclear reactor. In reactor, fuel doesn’t produce as many neutrons - neutron absorber is also used to absorb some of the neutrons - so reaction doesn’t run away. A nuclear reactor cannot explode!

NATS From the Cosmos to Earth Nuclear Fusion In nuclear fusion - two atoms collide and combine to form single atom/element - tremendous amount of energy released. Velocity or KE of atoms and/or pressure must be large enough to overcome repulsive electromagnetic force of outer cloud of electrons - such as in center of Sun. Mass of resultant atom slightly less (~ 3%) than two original atoms together - mass converted to energy. Note that the fusion reaction in a hydrogen bomb is started by an atomic bomb.

NATS From the Cosmos to Earth Light

NATS From the Cosmos to Earth Four Ways in Which Light can Interact with Matter 1. emission – matter releases energy as light 2. absorption – matter takes energy from light 3. transmission – matter allows light to pass through it 4. reflection – matter repels light in another direction

NATS From the Cosmos to Earth Mirror reflects light at angle equal to incoming angle - Most materials reflect light randomly - scattering. Movie screen scatters light into array of beams that reaches every member of the audience

NATS From the Cosmos to Earth Materials that transmit light are transparent Materials that absorb light are opaque In general - some combination of reflection, absorption, and transmission Red glass transmits red light - absorbs all other colors Green grass reflects green light - absorbs all other colors

NATS From the Cosmos to Earth Light What is light? - A vibration in an electromagnetic field through which energy is transported. Light as a wave Light as a particle E = hf photon f = c The dual nature of light or wave-particle duality: