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Temperature in Thermal Systems 1.4.1 Objectives • Define thermal energy. • Name the property of a body that determines its temperature. • Given Celsius or Fahrenheit temperatures and the formula for conversion, find the equivalent temperature on the alternate scale. • Explain the difference between heat and thermal energy. Work and Energy • Work on an object can change its position or speed. • Energy – property that enables an object to do work. • Increasing energy doing work: • hammer by lifting. • gas by compressing. • recharging a battery by forcing electrons in the reverse direction. Forms of Energy • Potential energy – a change in position can cause an body to gain energy resulting in a potential to do work. • Kinetic energy – the energy of motion; an body in motion has the ability to do work. • KE as a model of random motion of atoms and molecules. • Rate of this motion determines state of matter. • Thermal motion – random motion of an objects atoms and molecules. • Thermal energy – total energy of the thermal motion of all particles that make up an object. Temperature Less thermal energy More thermal energy Thermal energy always flows from “hotter” to “colder” bodies. • Temperature – measure of the average kinetic energy of thermal motion in an object. • Size of pie and thermal energy and average thermal motion (KE; see p. 66) Measuring Temperature • Thermal energy, as all forms of energy, is measured in Joules (J). • Temperature is measured in degrees. • Thermometer – device used to measure temperature; uses the expansion and contraction of a liquid, usu. colored alcohol or mercury (Hg). • Thermal equilibrium – when the average KE between to bodies is equal. Temperature Scales To convert from Fahrenheit to Celsius: 5 TC (TF 32) 9 To convert from Celsius to Fahrenheit: 9 TF TC 32 5 Heat • Heat – Q, the energy that flows from one object to another because of a temperature difference. • Again from higher avg. KE to lower avg. KE. • Not another word for thermal energy. • Thermal energy in transit; measured also in Joules (J). • Three ways in which heat is transferred: • Conduction • Convection • Radiation • The greater the temperature difference between two bodies in contact, the greater the heat transferred. • Prime mover in thermal systems. Exercises • Answer 1-12, pp. 76-78.