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Temperature and thermal equilibrium Hot Cold
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Temperature is proportional to the kinetic energy of atoms and molecules: T~KE
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Thermometer
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Celsius, Fahrenheit, Kelvin Andres Celsius (1701-1744). Celsius’ scale relates to the freezing temperature of water 0 ° C and the boiling temperature of water 100°C
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Daniel Fahrenheit Daniel Gabriel Fahrenheit (1686-1736) 1709 - invented the alcohol thermometer 1714 - mercury thermometer 1724 - he introduced the temperature scale that bears his name - Fahrenheit Scale. Fahrenheit’s scale places the freezing point of water at 32ºF and the boiling at 212ºF. Exactly 180ºF apart.
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T F =9/5 In Russia schools are closed when temperatures reaches -35ºC What is the temperature in Fahrenheit's?
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Lord Kelvin Kelvin’s scale related to the absolute zero – the point where nothing else can be colder. T (°C) P(Pa) -273.15
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Conversion of T scales:
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Thermal expansion
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As temperature increases, the volume of the object increases as well. The extent of thermal expansion is characterized by the coefficient of volume expansion CVE gases >>> CVE liquids >> CVE solids ?? Why do train wheels rhythmically clink on the rails? ?? Why putting a jar under hot water makes it easier to open it? ?? When do you get more gas for your money: on a cold or a hot day?
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Thermal equilibrium T1T1 T2T2 T 1 <T 3 <T 2 the state in which two bodies in contact with each other have identical temperatures
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HEAT The process by which energy is exchanged between objects because of a difference in their temperatures. SI: [J] – joules » James Joule
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Conduction the process whereby energy is transferred directly through a material without any bulk motion of its particles. Conduction is mostly common in solids. Depending on whether materials conduct heat easily, they are divided into conductors and insulators.
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Convection process in which energy is transferred through a material with any bulk motion of its particles. Convection is common in fluids
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Radiation the process in which energy is transferred by means of electromagnetic waves.
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Internal energy: the energy of a substance due to the random motions of its component particles (atoms and molecules) and equal to the total energy of those particles. U – internal energy 1 2 1) T 1 =T 2 Compare U 1 and U 2 2) U 1 = U 2, Compare T 1 and T 2
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Heat / Energy / Work units
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Conservation of energy KE + PE + Work = const Work – way to change U of the system For an isolated system (no energy is lost ) If a total mass of 11.5 kg falls through 1.3 m and all of the ME is converted into U of water, by how much will U of water change? What will you observe in the apparatus?
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Specific Heat Capacity C p shows how much heat is needed to change the temperature of 1 kg of substance by 1ºC
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Examples: How much heat does it take to heat a 580 g aluminum pot (c p =0.92 J/gK) from 20ºC to 180º C? A lead bullet (c p =0.13 J/gK) going 460 m/s strikes a tree. If all the heat generated remains in the bullet, how much does its temperature rise?
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3 States of
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Phase Change The physical change of substance from one state (solid, liquid, or gas) to another at constant temperature and pressure
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Heat Q(J) T(°C) 0ºC
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Q(J) 0ºC T(°C)
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Q(J) 0ºC T(°C)
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At what point will the temperature stop rising? Q(J) 0ºC T(°C) 100ºC
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Q(J) 0ºC T(°C) 100ºC
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Heat of fusion – the energy per unit mass transferred in order to change a substance from solid to liquid or from liquid to solid at constant temperature and pressure
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Heat of vaporization – the energy per unit mass transferred in order to change a substance from liquid to vapor or from vapor to liquid at constant temperature and pressure
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