Heat Transfer Notes
Energy at the Earth’s Surface Remember that only a small percentage of the sun’s energy stays on Earth. Some is reflected back out into space. Also, some of the energy absorbed by the surface of Earth is reradiated BACK into space in the form of infrared radiation.
Greenhouse effect/radiation balance
Thermal Energy and Temperature The temperature of something is the measure of the average kinetic energy of each of its individual particles. Because all particles must vibrate to exist, all particles have a temperature. 0 Kelvin ( °C, °F) is the coldest [theoretical] possible temperature. At this temperature, all molecular motion ceases.
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 °F = (°C × 9/5) + 32 °C = (°F − 32) × (5/9) °C = K − K = °C Deduct 32, then multiply by 5, then divide by 9 Multiply by 9, then divide by 5, then add 32
Practice Problems 1. 72°F = ____°C 2. 5°F = ____°C 3. 16°C = _____°F 4. 30°C = _____K 5. 4°C = _____°F °F = _____K
Thermal Energy and Temperature A few temperatures to know instantly: 0°C = 32°F 100°C = 212°F -40°C = -40°F °C = 0K
How Heat is Transferred Most of the heat you feel from the sun travels to you as radiation. Radiation is the direct transfer of energy by electro-magnetic waves. Remember that EM radiation does not need matter to travel through. It has the ability to transfer energy through a vacuum.
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 how by conduction.
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 Sunlight heats Earth’s surface by radiation. The warm surface then heats the atmosphere by both conduction (touching the air molecules) and radiation. 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. The troposphere is the lowest layer of the atmosphere, where most weather occurs, and contains almost all of the mass of the atmosphere.
How Heat is Transferred Heat is transferred by convection through most of the troposphere. Convection currents move heat throughout the troposphere. The upward mov’t of warm fluids and downward mov’t of cool fluids form convection currents.