Chapter 6: Thermal Energy

Section 1: Temperature and Heat What is Temperature and how is it related to heat? In all materials: solids, liquids and gases particles are in constant motion

Temperature -of an object is related to the average kinetic energy of the atoms or molecule the faster the particles move, the more kinetic energy they have, the higher temp of the object Ex: cup of hot tea and glass of ice tea

Thermal Energy The sum of all kinetic and potential energy of all the molecules in an object is its thermal energy When the TEMP of an object increases, avg. kinetic energy increases SO: thermal energy also increases (sum of kinetic and potential energy)

Similarly, if the mass of an object increases, the thermal energy of the the object also increases Ex: beakers w/different water levels

Heat -is thermal energy that flows from something at a higher temp to something at a lower temp Heat is a form of energy, so it is measured in Joules Heat ALWAYS flows from warmer to cooler materials Ex: homemade ice cream

Specific Heat Definition:-the amount of heat needed to raise the temperature of 1 kg of some material by 1 degree C or 1 degree Kelvin Measured in J/kg (joules per kilogram Kelvin)

Water and Specific Heat Water is useful as a coolant since it has a higher specific heat than other substances It can absorb heat w/out a large change in temperature (ex: lakes) Ex: cooling system in cars Change in thermal energy = mass X change in temp X specific heat

To measure specific heat, a CALORIMETER can be used—see pg. 163

Section 2: Transferring Thermal Energy Conduction: the transfer of thermal energy through matter by the direct contact of particles (mostly through solids) Occurs because all matter is made of atoms and molecules that are in constant motion Transfer by collision grabbing a handful of snow

Heat can be transferred by conduction from one material to another or through one material Good Heat conductors: silver, copper and aluminum Poor Heat conductors: wood, plastic, glass and fiberglass

Convection: the transfer of energy in a fluid by the movement of heated particles (in conduction particles collide w/ea other and transfer energy) In Convection: more energetic fluid particles move from one location to another and carry their energy with them

Convection transfers heat from warmer to cooler parts of the fluid As a result, particles move faster, fluids expand and density increases Ex: Lava Lamp—pg. 165

Radiation: the transfer of energy by electromagnetic waves (through air) These waves can travel through space, even when no matter is present Radiant energy: energy that is transferred by radiation ex: when you stand near a fire and feel warm

When radiation strikes a material, some of the energy is absorbed, some is reflected and some may be transmitted through the material In a solid, liquid or gas, radiant energy can travel through the space between molecules and is absorbed and re-emitted by other molecules

Therefore, radiation usually passes more easily through gases than through solids or liquids since particles are farther apart

Controlling heat flow: Insulators: materials that do not allow heat to flow through easily GOOD CONDUCTORS = BAD INSULATORS Gases are usually better insulators than solids or liquids Ex: jacket, fiberglass insulation in buildings, thermos bottle, etc.—pg. 176

Section 3: Using Heat Heating systems: all heating systems require some source of energy Ex: wood, coal, burning fuel, Forced air system: Fuel is burned in a furnace and heats a volume of air A fan then blows the warm air through a series of large pipes/ducts Cool air returns to the furnace through additional vents

Radiator systems: a closed metal container that contains hot water and steam Thermal energy contained in the hot water or steam is transferred to the air surrounding the radiator by conduction Ex: small scale—electric radiators

Electric Heating Systems: uses electrically heated coils placed in ceilings and floors to heat the surrounding air by conduction Convection then distributes the heated air through the room

Solar Heating: In passive solar heating systems, solar energy heats rooms inside a building, but no mechanical devices are used to move heat from one area to another Ex: greenhouse Homes often have a wall of windows on the south side of the house for passive solar heating

In active solar heating, solar collectors absorb radiant energy from the sun The absorbed radiant energy heats water in pipes and a pump circulates the warm water to radiators in rooms of the house Some systems have large, insulated tanks for storing heated water Solar panels absorb heat to heat water in pipes

Heat Engine -an engine that converts thermal energy into mechanical energy Internal combustion engine—burns fuel inside the engine in chambers or cylinders (more cylinders = more power) Some of the power produced is given off as heat, therefore engines need cooling systems

Heat Movers: A device that removes thermal energy from one location and transfers it to another location at a different temperature Ex: Refrigerators use a coolant (liquid that evaporates at a low temperature) to cool the inside of the fridge as it changes state between liquid and gas

HEAT PUMPS: a two-way heat mover Air Conditioners : Operate similar to a refrigerator warm air from the room is forced to pass over tubes containing coolant Works like a heat engine in reverse using mechanical energy supplied by a compressor motor to move thermal energy from cooler to warmer areas. HEAT PUMPS: a two-way heat mover In warm weather, operates like an air conditioner, and in winter, operates like a heater

The Human Coolant Your body uses evaporation to keep its internal temperature constant As you sweat, it evaporates and carries away heat, making you cooler Thermal energy that is lost by your body becomes part of the thermal energy of your evaporated sweat