Heat and Temperature

Temperature A measure of average kinetic energy of the molecules in a substance. In open air water cannot reach temperatures above boiling because the fastest moving water molecules leave through evaporation. In open air water cannot reach temperatures above boiling because the fastest moving water molecules leave through evaporation. Absolute zero occurs when there is no energy in a substance. The molecules are stationary or there are no molecules present. The molecules are stationary or there are no molecules present. Vacuum is the absence of matter.

Temperature Scales Fahrenheit Freezing 32 o F Freezing 32 o F Boiling 212 o F Boiling 212 o F Fahrenheit to Celsius conversion Fahrenheit to Celsius conversion o C = 5/9( o F ) + 32 Kelvin Absolute zero Absolute zero Celsius to Kelvin conversion Celsius to Kelvin conversion K = o C Centigrade (Celsius) Freezing 0 o C Freezing 0 o C Boiling 100 o C Boiling 100 o C Celsius to Fahrenheit conversion Celsius to Fahrenheit conversion o F = 9/5( o C - 32)

Feel The Heat Heat is the transfer of energy between two substances of different temperatures. Energy travels from warmer to cooler substances. There are three forms of heat transfer Convection Convection Conduction Conduction Radiation. Radiation.

Energy Transfer Convection: Heat transfer through fluids Includes gases. Includes gases. Convective Cells Convective Cells Hot air or fluids rise because they are less dense. Colder denser air or fluid flows in from underneath to take its place. Heat transfer through the atmosphere responsible for weather patterns. Heat transfer through the atmosphere responsible for weather patterns. How thunderstorms are created. Responsible for currents in the ocean essential for life. Responsible for currents in the ocean essential for life. Evaporative cooling occurs due to convection

Energy Transfer Conduction: Heat transfer through the contact of two substances. As molecules gain kinetic energy they transfer that energy to other molecules and set them in motion. As molecules gain kinetic energy they transfer that energy to other molecules and set them in motion. Conduction can lead to convection Conduction can lead to convection Consider boiling a pot of water on a stove. The molecules of a metal pot transfer their kinetic energy to the water molecules.

Heat Transfer Radiation: Transfer of heat through electromagnetic waves. Unlike convection and conduction no molecules are necessary for heat transfer. Unlike convection and conduction no molecules are necessary for heat transfer. Can travel through a vacuum. This is infrared energy. Infrared images can locate tumors or see it circulation is restored in damaged limbs. Infrared images can locate tumors or see it circulation is restored in damaged limbs.

Conductors Conductors are substances that are that can transfer heat. Metals are good conductors of heat. Metals are good conductors of heat. Gases are poor conductors of heat because the particles are too far apart. Gases are poor conductors of heat because the particles are too far apart. Contact between molecules are necessary for heat conduction. Liquids are better conductors of heat than gases but do not conduct heat as well as solids because they are not as compact. Liquids are better conductors of heat than gases but do not conduct heat as well as solids because they are not as compact.

Insulators Insulators Insulators do no conduct heat well. Conductors are poor insulators. Conductors are poor insulators. Some good insulators are Air Air Foam Foam Rubber Rubber Wood Wood Insulation is used in houses to prevent heat loss. R value is a number that builders use to rate how effective an insulating material is. R value is a number that builders use to rate how effective an insulating material is. The higher the R value the better the insulation material. SubstanceR Value Flat glass 0.89 Flat glass 0.89 Insulating Glass 1.54 Dry wall 0.45 Dry wall 0.45 Fiberglass 10.90

Specific Heat Refers to the amount of energy necessary to raise the temperature of a substance. The amount of energy in joules to raise 1 kg of substance 1 degree Kelvin. The amount of energy in joules to raise 1 kg of substance 1 degree Kelvin. Substances with a high specific heat require a lot of energy to change its temperature. Substances with a high specific heat require a lot of energy to change its temperature. Water has a high specific heat Rubbing alcohol has a low specific heat. Specific Heat Equation Specific Heat Equation Energy = specific heat x mass x temperature change E c m T

Air Conditioners Remember, when a substances turns from a liquid to a gas, energy is absorbed. When gas condenses into a liquid energy is released. Air conditioners absorb energy from the air in you house making the air in your house cooler by using a liquid that evaporates easily. The liquid condenses with temperature of the air out side releasing energy.

Central Heating Systems A furnace heats steam, water or air in pipes or ducts that are circulated throughout the house. Because the pipes are hotter than the surrounding air heat leaves the pipe to warm the surrounding air. Solar panels collect heat from the suns energy and it is stored and then transferred to pipes or ducts much like a central heating system.