Heat Transfer Notes
Thermal Energy and Temperature The temperature of something is the measure of the average kinetic energy of each of its individual particles. Kinetic energy is the energy of motion. Because all particles must vibrate to exist, all particles have a temperature. 0 Kelvin (-273.15°C) is the coldest [theoretical] possible temperature. At this temperature, all molecular motion ceases.
Types of Heat Transfer When an object heats up, particles in the object have more energy and move faster. The energy can travel, or transfer from a warmer object to a cooler object. Energy NEVER transfers from cooler to warmer.
Slower Faster
Thermal Energy and Temperature On the other hand, thermal energy is the total energy of motion of the particles of a substance. For example, hot tea in a full teapot has more thermal energy than the hot tea in a teacup. This is because the tea in the pot has more particles, therefore its total energy will be higher.
Thermal Energy and Temperature A thermometer is an instrument that measures temperature. Temperature is measured in units called degrees. There are three temperature scales: Celsius, Fahrenheit, and Kelvin. Scientists use Celsius and Kelvin.
Thermal Energy and Temperature A few temperatures to know instantly: 0°C = 32°F Water Freezes/Melts 100°C = 212°F Water Boils
How Heat is Transferred Radiation is the transfer of energy through space. For example, sunlight travels through space by radiation and warms Earth’s surface. Radiation also explains why your hands get warm when you hold them near a fire.
How Heat is Transferred Conduction is the direct transfer of heat from one thing to another by touching. When you walk on hot sand, your feet get hot by conduction. The troposphere is the lowest layer of the atmosphere, where most weather occurs, and contains almost all of the mass of the atmosphere. Only the first few meters of the troposphere are heated by conduction. The air closer to the ground is usually warmer than the air above it.
How Heat is Transferred Convection is the transfer of heat by the movement of a fluid. A fluid is a liquid or gas (or plasma). The particles of a fluid take heat with them as they move. If you heat the air in one room, the air will heat the next room as the air flows from one room to the next. This is heating by convection.
How Heat is Transferred Heat is transferred by convection through most of the troposphere. Convection currents move heat throughout the troposphere. The upward movement of warm fluids and downward movement of cool fluids form convection currents.
Convection Currents A convection current starts when there are differences in temperature and density of a fluid. Density is the amount of mass in a given volume of a substance (how tightly packed the particles are). A high-density substance feels heavy for its size. soccer ball vs. bowling ball
Convection Currents Which is less dense: hot air or cold air? Which is less dense: hot air or warm air? Because particles move faster when they are warmed up, they also tend to spread out, therefore the warmer a fluid becomes, the less dense it will become as well.
Convection Currents Suppose you put a pot of soup on the stove. The soup at the bottom of the pot will get warm first. Because it is warmer, the soup at the bottom of the pot is less dense than the cooler soup above it. So the warmer soup rises. At the same time, the cooler, denser soup sinks to the bottom of the pot.
Convection Currents The cooler soup now at the bottom gets warmer, and the process repeats. A constant flow of particles begins. Warmer soup keeps rising, and cooler soup keeps sinking. This movement of particles transfers heat throughout the soup. This is the same process that occurs with cooling houses from the ceiling and heating them from the floor.