Download Heat Transfer - Madison County Schools

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 (-273.15°C) 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
• A few temperatures to know instantly:
• 0°C = 32°F
• 100°C = 212°F
• -40°C = -40°F
• -273.15°C = 0K
Thermal Energy and
Temperature
• °F = (°C × 1.8) + 32
• °C = (°F − 32) × (5/9)
• °C = K − 273.15
• K = °C + 273.15
Practice Problems
1. 72°F = ____°C
2. 5°F = ____°C
3. 16°C = _____°F
4. 30°C = _____K
5. 4°C = _____°F
6. 112°F = _____K
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 electromagnetic 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.
• 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.