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 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.  T C = T K

Temperature Scales

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(T final – T initial ) Measured in Joules, J.

Practice Problems  Pg 280  5-6