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Temperature and Thermal Energy. Section 12.1 Physics. Objectives (What we’re shootin’ for). Describe the nature of thermal energy. Define temperature and distinguish it from thermal energy. Use the Celsius and Kelvin temperature scales and convert one to another.
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Temperature and Thermal Energy Section 12.1 Physics
Objectives (What we’re shootin’ for) • Describe the nature of thermal energy. • Define temperature and distinguish it from thermal energy. • Use the Celsius and Kelvin temperature scales and convert one to another. • Define specific heat and calculate heat transfer.
What Makes Something Hot? • Thermodynamics: The study of heat. • Kinetic-Molecular Theory: Based on the assumption that all matter is composed of small particles that are always in motion. • In a warm body, the small particles are moving faster than they are in a cold body.
Kinetic-Molecular Theory in States of Matter • The Kinetic-Molecular Theory holds true in all three states of matter. • Arrangement of Molecules • The overall energy of motion of the particles that make up an object: Thermal Energy.
Thermal Energy and Temperature • Keep in mind that the thermal energy of an object does not mean that all particles are moving at the same speed. • Thermal energy is only the average energy of particles in an object. • Temperature: the measure of “hotness or coldness” of an object.
Temperature • A hot object has a greater average kinetic energy reading than a cold object.
Equilibrium and Thermometry • If you have a fever, and you place a thermometer in your mouth to take your temperature, how is the energy of your body transferred to the thermometer? • Conduction: Particles collide and energy from your body is transferred to the thermometer.
Equilibrium and Thermometry • When the thermometer and your skin are at equal thermal energy transfer, Thermal Equilibrium has been reached. • Once equilibrium has been reached, does energy transfer stop? • No. The rates at which the exchange of thermal energy take place are equal.
Equilibrium and Thermometry • A Thermometer is a device that measures temperature when it is placed in contact with an object and allowed to come to thermal equilibrium with that object.
Temperature Scales • Three temperature scales: Celsius, Fahrenheit, and Kelvin. • Celsius Scale was developed based on the properties of pure water. • Boils at 100°C • Freezes at 0°C
Temperature Scales • Kelvin is the SI unit of temperature. • At 0 Kelvin, Absolute Zero, all thermal energy of matter ceases to exist. • 0 K = -273°C • On the Kelvin Scale, water freezes at 273 K. • On the Kelvin Scale, water boils at 373 K. • TC + 273 = TK
Temperature Scales http://www.visionlearning.com/library/modules/mid48/Image/VLObject-318-021121021101.gif
Practice Problems • 1-4 • Pg. 278
Heat and Thermal Energy • Thermal energy always flows from an area of higher thermal energy to an area of lower thermal energy. • Heat: the energy that flows between two objects as a result of a difference in temperature. • Heat is denoted as “Q”
Heat and Thermal Energy • If Q is a positive value, heat has been absorbed by an object. • If Q is a negative value, heat has left the object. • Heat is measured in Joules, J.
Heat and Thermal Energy • Thermal Energy Transfer: • Conduction: through direct contact of particles. • Convection: through currents in a fluid. • Radiation: through electromagnetic waves.
Specific Heat • When heat flows into an object, its thermal energy increases, and so does its temperature. • The amount of increase depends on: • The size of the object. • The material from which the object is made. • The specific heat of a material. • Specific Heat: the amount of energy that must be added to the material to raise the temperature of a unit mass one temperature unit.
Specific Heat • Specific Heat’s symbol is “C” • Each material has a different value for its specific heat. • The change in thermal energy can be calculated using: • Q = mC(Tfinal – Tinitial) • Measured in Joules, J.
Practice Problems • Pg 280 • 5-6