Temperature and Thermal Energy

1. Temperature and Thermal Energy Section 12.1 Physics

2. 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.

3. 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.

4. 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.

5. 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.

6. Temperature • A hot object has a greater average kinetic energy reading than a cold object.

7. 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.

8. 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.

9. 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.

10. 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

11. 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

12. Temperature Scales http://www.visionlearning.com/library/modules/mid48/Image/VLObject-318-021121021101.gif

13. Practice Problems • 1-4 • Pg. 278

14. 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”

15. 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.

16. Heat and Thermal Energy • Thermal Energy Transfer: • Conduction: through direct contact of particles. • Convection: through currents in a fluid. • Radiation: through electromagnetic waves.

17. 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.

18. 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.

19. Practice Problems • Pg 280 • 5-6