Thermal Energy and Heat Notes

Temperature   Temperature is a measure of the average kinetic energy of the individual particles in matter.   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.

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

Temperature   Absolute zero – 0 Kelvin (-273 o C) - the temperature at which no more energy can be removed from matter  Do you think it is possible to achieve a temperature of Absolute Zero?

Thermal Energy   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.

Specific Heat Specific heat – the amount of energy required to raise the temperature of 1 kilogram of a material by 1 Kelvin. 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 foam for coolers instead of steel or copper?

Heat Transfer Heat can be transferred in three ways: Conduction Convection Radiation

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.

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.

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 By the way, heat travels in only one direction – away from the warmer object or substance to the cooler object or substance. From a hot bowl of Irish Stew to the surrounding air or From the surrounding air to a cold bowl of ice cream

Conductors and Insulators Substances that transfer thermal energy well are called conductors : SilverStainless SteelGold Copper Other metals Dense Materials Insulators do not allow the transfer of heat energy well: Wood Wool Straw PaperGases Low Density Materials

Conductors and Insulators Remember the three states of matter ? Solid – particles packed tightly together Liquid – particles close, but not held in the same position Gas – fast moving particles distant from each other And, what about Phase Changes ? Freezing – liquid becomes a solid Melting – solid becomes a liquid Boiling – liquid becomes a gas What state of matter would make the best insulator?

Changes of Phase Remember this lab on freezing, melting and boiling points? When substances are heated and a phase change occurs, thermal energy increases while temperature stays the same. So, what’s happening during the flat section?

Thermal Expansion As the thermal energy of matter increases, its particles spread out and the substance expands. This is called thermal expansion – like that copper sphere Mr. Thurston is trying to force through the loop. 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.

Heat Engines Heat has been used for many years to make machines move. A heat engine transforms thermal energy to mechanical energy. An external combustion engine burns fuel outside the engine, like a steam engine used to power steam locomotives. 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.

Heat Engines 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.