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Lecture 7: Matter and Energy

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Last Time… forms of energy: forms of energy: kinetic potential radiative Law of Conservation of Energy Law of Conservation of Energy energy is not created or destroyed, only transformed

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Temperature and Thermal Energy Temperature measures the average kinetic energy of molecules or atoms in a material (independent of mass) Temperature measures the average kinetic energy of molecules or atoms in a material (independent of mass) Thermal energy or heat measures the total amount of energy in a material (depends on mass) Thermal energy or heat measures the total amount of energy in a material (depends on mass)

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Temperature Scales

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Mass as Potential Energy Einstein showed that mass and energy can be converted from one to the other Einstein showed that mass and energy can be converted from one to the other the amount of energy obtained from converting a given amount of mass to pure energy is given by the famous formula the amount of energy obtained from converting a given amount of mass to pure energy is given by the famous formula E = m c 2 where m is the mass and c is the speed of light, c = 3 x 10 8 m/s

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Using Einstein’s Equation How much energy (in Joules) is released by a 1-megaton H-bomb that converts 0.1 kg of mass into energy? How much energy (in Joules) is released by a 1-megaton H-bomb that converts 0.1 kg of mass into energy? E = m c 2 = 0.1 kg x (3.0 x 10 8 m/s) 2 = 9 x 10 16 kg m 2 /s 2 = 9 x 10 16 J

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What is Matter? all matter is made of atoms all matter is made of atoms each different kind of atom corresponds to a different chemical element each different kind of atom corresponds to a different chemical element atoms can also be combined to form molecules atoms can also be combined to form molecules

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Atoms are not indivisible… protons (massive, positive electric charge) protons (massive, positive electric charge) neutrons (massive, neutral electrically) neutrons (massive, neutral electrically) electrons (light, negative electric charge) electrons (light, negative electric charge)

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Atomic mass and number the identity of an element is determined by the number of protons (atomic number) the identity of an element is determined by the number of protons (atomic number) the atomic mass of an element is the mass of the protons plus neutrons (electrons have negligible mass) in units of the proton mass the atomic mass of an element is the mass of the protons plus neutrons (electrons have negligible mass) in units of the proton mass an element with the same number of protons but a different number of neutrons is called an isotope an element with the same number of protons but a different number of neutrons is called an isotope

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Ways to convert mass to energy nuclear fusion nuclear fusion two atoms are combined to produce a heavier atom, releasing energy process that stars use to produce light nuclear fission nuclear fission the nucleus of an atom is split apart, releasing energy used in nuclear power plants

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Fission and Fusion

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Radioactive Decay

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Energy Comparisons 1.0 x 10 6 J burning 1 liter of oil 1.2 x 10 7 J fusion of hydrogen in 1 liter of water 7 x 10 13 J Annual output of the Sun 10 34 J 10 34 J metabolism of a candy bar

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Fusion: the perfect energy source Suppose that we could build a power plant fueled by fusion of the Hydrogen in water. How much water per minute would we need to meet the entire energy demand of the USA? Suppose that we could build a power plant fueled by fusion of the Hydrogen in water. How much water per minute would we need to meet the entire energy demand of the USA?

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Phases of Matter solid solid liquid liquid gas gas plasma plasma Increasing temperature

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sublimation evaporation molecular dissociation ionization solid liquid gas plasma 100 K 10 3 K 10 4 K 10 6 K

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Density mass density = mass per unit volume mass density = mass per unit volume units g/cm 3 or kg/m 3 density of water is 1 g/cm 3 energy density = energy per unit volume energy density = energy per unit volume units J/ m 3

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What phase is dominant? on Earth? on Earth? in our Solar System? in our Solar System? in our Galaxy? in our Galaxy? in clusters of Galaxies? in clusters of Galaxies? in the Universe? in the Universe?

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Coma Cluster

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