1. Thermal Energy and Heat

2. Temperature Temperature is a measure of the average kinetic energy of the individual particles in matter. The higher the temperature, the more kinetic energy the substance has and the faster its particles are moving. We use thermometers to measure temperature or kinetic energy – as the liquid in the thermometer heats up, its particles move faster causing them to spread out – so, the liquid rises.

3. Measuring Temperature There are three common scales for measuring temperature: 1. Fahrenheit – common in the U.S. – water freezes at 32 o F and boils at 212 o F 2. Celsius – common in the world – larger degrees than Fahrenheit water freezes at 0 o C and boils at 100 o C 3. Kelvin – most useful in physics – same degrees as Celsius, 1 o C equals 1Kelvin – water freezes at 273 K and boils at 373 K.

4. Absolute Zero Absolute zero – 0 Kelvin (-273 o C) - the temperature at which no more energy can be removed from matter Can a temperature of ABSOLUTE ZERO be reached? Video Video Clip Video

5. Converting Temperature To convert from Fahrenheit to Celsius, use this formula: o C = 5 / 9 ( o F – 32)

6. Temperature – thermal energy – heat Temperature, thermal energy, and heat are related concepts, but they are not the same: Thermal energy is the total energy of all the particles in an object – however, it depends on the number of particles in the object. On the other hand, heat is the transfer of thermal energy from one type of matter to another – or, thermal energy moving from a warmer object to a cooler object. When objects are heated, their temperatures do not increase at the same rate.

7. Specific Heat Specific heat – the amount of energy required to raise the temperature of 1 kilogram of a material by 1 Kelvin. The SI unit for specific heat is joules per kilogram-Kelvin, or J/(kg-K)

8. Specific Heat Notice that the specific heat of water is pretty high but that of silver is low. There is an inverse relationship between an object’s or substance’s specific heat and density. The higher an object’s density, the lower its specific heat. So, why do we use styrofoam for coolers instead of steel or copper?

9. The Transfer of Heat Heat can be transferred in three ways: Conduction Convection Radiation

10. Conduction When heat is transferred from one particle of matter to another without the movement of the matter it is called conduction.   Fast moving particles in a stove burner’s coil collide with the slow moving particles in a cool pot containing water.   Fast moving particles in a cup of coffee collide with slow moving particles in your tongue giving you a burn.

11. Convection In convection, heat is transferred by the movements of currents within a fluid.   Water heated in a pot on a stove creates currents – convection currents – which transfer heat within the fluid.   In these currents, hot water rises while the cooler water on top flows to the bottom – this creates the circular motion called currents.

12. Radiation Radiation is the transfer of energy by electro- magnetic waves.   You can feel the heat of a fire from several meters away   On sunny days you can feel the rays of the sun and get a tan

13. Heat Travels….. By the way, heat travels in only one direction – away from the warmer object or substance to the cooler object or substance. From the sun to the surface of the earth OR From the surrounding air to a cold bowl of ice cream

14. Conductors Substances that transfer thermal energy well are called conductors: Silver Stainless SteelGold Copper Other metals Dense Materials

15. Insulators Insulators do not allow the transfer of heat energy well: Wood WoolStraw Paper Gases Low Density Materials

16. Three States of Matter States Solid – particles packed tightly together Liquid – particles close, but not held in the same position Gas – fast moving particles distant from each other Phase Change Freezing – liquid becomes a solid Melting – solid becomes a liquid Boiling – liquid becomes a gas Also, remember when liquids become gases, we say they evaporate and when gases become liquids we call it condensation.

17. Phase Changes Remember this lab on freezing, melting and boiling points? During a phase change, thermal energy increases while temperature stays the same.

18. Thermal Expansion As the thermal energy of matter increases, its particles spread out and the substance expands. This is called thermal expansion – watch this video of thermal expansion.

19. Refrigerants Refrigerants can be used to absorb heat in one place and release it in another. Refrigerators use these substances to transfer heat to the outside.

20. Uses of Heat Heat has been used for many years to make machines move. A heat engine transforms thermal energy to mechanical energy. This Steam Locomotive uses steam to transform thermal energy to mechanical energy. Coal is used to heat water, which changes into steam, expanding to push pistons back and forth. An external combustion engine burns fuel outside the engine, like a steam engine used to power steam locomotives.

21. Internal Combustion Engine Internal combustion engines burn fuel inside the cylinders of the engine. This is the most common type of engine used in today’s automobiles. The piston inside the cylinder moves up and down by the combustion of fossil fuels. This motion is then transferred to the wheels moving the car.