Thermal Energy Chapter 16

Temperature – related to the average kinetic energy of an object’s atoms or molecules, a measure of how hot (or cold) something is Temperature – related to the average kinetic energy of an object’s atoms or molecules, a measure of how hot (or cold) something is Thermal energy – the sum of the kinetic and potential energy of all the atoms in an object Thermal energy – the sum of the kinetic and potential energy of all the atoms in an object –Thermal energy increases as temperature increases –At constant temperature, thermal energy increases if mass increases

Heat - thermal energy that flows from something at a higher temperature to something at a lower temperature Heat - thermal energy that flows from something at a higher temperature to something at a lower temperature Specific heat – amount of heat needed to raise the temperature of 1kg of a material by 1 degree C or K Specific heat – amount of heat needed to raise the temperature of 1kg of a material by 1 degree C or K Specific Heat Equation energy = (specific heat)  (mass)  (temperature change) energy = cm  t

Fahrenheit and Celsius are common scales used for measuring temperatures. Fahrenheit and Celsius are common scales used for measuring temperatures. On the Fahrenheit scale, water freezes at 32 º F and boils at 212 º F. On the Fahrenheit scale, water freezes at 32 º F and boils at 212 º F. The Celsius scale, which is widely used in science, gives a value of 0 º C to the freezing point of water and a value of 100 º C to the boiling point of water at standard atmospheric pressureThe Celsius scale, which is widely used in science, gives a value of 0 º C to the freezing point of water and a value of 100 º C to the boiling point of water at standard atmospheric pressure

Fahrenheit-Celsius Conversion Equations A degree Celsius is 1.8 times as large as a degree Fahrenheit. Also, the temperature at which water freezes differs for the two scales by 32 degrees. T F = Fahrenheit temperature t = Celsius temperature

The Kelvin scale is based on absolute zero. The Kelvin scale is based on absolute zero. Absolute zero is the temperature at which molecular energy is at a minimum (0 K on the Kelvin scale or – º C on the Celsius scale). Absolute zero is the temperature at which molecular energy is at a minimum (0 K on the Kelvin scale or – º C on the Celsius scale). Celsius-Kelvin Conversion Equation T = t T = Kelvin temperature t = Celsius temperature

Changes in thermal energy can be calculated as change in thermal energy = mass X change in temperature X specific heat Changes in thermal energy can be calculated as change in thermal energy = mass X change in temperature X specific heat –When heat flows into an object and its temperature rises, the change in temp is positive –When heat flows out of an object and its temperature decreases, the change in temperature is negative Calorimeter –used to measure specific heat Calorimeter –used to measure specific heat

Conduction – transfer of thermal energy through matter by direct contact of particles Conduction – transfer of thermal energy through matter by direct contact of particles –Kinetic energy is transferred as particles collide –Solids, particularly metals, are good heat conductors Convection – the transfer of energy by the motion of heated particles in a fluid Convection – the transfer of energy by the motion of heated particles in a fluid –Transfer heat from warmer to cooler parts in a fluid –Create rain forests and deserts over different regions of Earth

Radiation – energy transfer by electromagnetic waves Radiation – energy transfer by electromagnetic waves –Some radiation is absorbed and some is reflected when it strikes a material –Heat transfer by radiation is faster in a gas than in a liquid or solid Most living things control the flow of heat by using special features such as fur, blubber, or scales Most living things control the flow of heat by using special features such as fur, blubber, or scales

Insulator – material that does not let heat flow through it easily Insulator – material that does not let heat flow through it easily –Gases such as air usually make better insulators than liquids or solids –A vacuum layer in a thermos is a good insulator because it contains almost no matter to allow conduction or convection to occur

conductor Any material through which energy can be easily transferred as heat conductor Any material through which energy can be easily transferred as heat Poor conductors are called insulators. Poor conductors are called insulators. Gases are extremely poor conductors.Gases are extremely poor conductors. Liquids are also poor conductors.Liquids are also poor conductors. Some solids, such as rubber and wood, are good insulators.Some solids, such as rubber and wood, are good insulators. Most metals are good conductors.Most metals are good conductors.

Heating systems – warm homes and building Heating systems – warm homes and building –Forced-air system – fuel heats air, which is blown through ducts and vents; cool air is returned to the furnace to be reheated –Radiator system – hot water or steam in a radiator transfers thermal energy to the air –Electric heating system – electrically heated coils in ceilings or floors heat air by conduction

Solar energy – energy from the Sun Solar energy – energy from the Sun –Passive solar heating - does not use mechanical devices to move heat –Active solar heating - use solar collectors to absorb radiant energy, which is circulated through the building Active Solar Heating System

Heat engine – an engine that converts thermal energy into mechanical energy Heat engine – an engine that converts thermal energy into mechanical energy –Internal combustion engine – burns fuel inside the engine in chambers or cylinders –ICE converts only about 26% of the fuel’s chemical energy to mechanical energy

Internal Combustion Engine

Machines operate with two energy principles: Machines operate with two energy principles: The first law of thermodynamics states that the total energy used in any process— whether that energy is transferred as a result of work, heat, or both—is conserved. The first law of thermodynamics states that the total energy used in any process— whether that energy is transferred as a result of work, heat, or both—is conserved. The second law of thermodynamics states that the energy transferred as heat always moves from an object at a higher temperature to an object at a lower temperature. The second law of thermodynamics states that the energy transferred as heat always moves from an object at a higher temperature to an object at a lower temperature.

Air Conditioner One example is an air conditioner. An air conditioner does work to remove energy as heat from the warm air inside a room and then transfers the energy to the warmer air outside the room.

Passive Solar Heating