Temperature and Heat Transfer

Average global temperature of Earth:

59°F 15°C 288K

The solar radiation that reaches Earth is affected in one of the following ways:

- it can be reflected -it can be scattered -it can be absorbed

Reflection

-Clouds reflect about 20% of the incoming solar radiation back to space -On average, Earth's surface reflects about 4% of the incoming solar radiation back to space -The reflectivity or albedo of the Earth's surface varies with the type of material that covers it.

Scattered

-Scattering gives us our blue sky -The small gas atoms and molecules that make up the atmosphere preferentially scatter the shorter wavelengths of light -As the sun gets lower in the sky, the sunlight has to travel through more atmosphere -This gives the orange and red light more of a chance to be scattered.

The Sun

-an average star -about 5 billions years old; will probably shine for another 5 billion years before it enters the next stage of stellar evolution -contains about 98% of the total solar system mass -109 Earths would fit across the Sun's disk -Sun's outer visible layer is called the photosphere -temperature of 6,000°C (11,000°F) -Solar energy is created deep within the core of the Sun. It is here that the temperature (15,000,000° C; 27,000,000° F) and pressure (340 billion times Earth's air pressure at sea level) is so intense that nuclear reactions take place. -The Sun makes energy by the thermonuclear fusion of hydrogen into helium -Every second 700 million tons of hydrogen are converted into helium in the Sun's core -It takes nearly 100,000,000 years for energy created in the Sun's core to get to the surface of the Sun - It takes about 8 minutes for energy leaving the Sun's surface to reach Earth

Convection

-heat transfer that involves the actual movement or circulation of substance (most common form of transfer in the atmosphere) -depends on the fact that, in general, fluids expand when heated and thus undergo a decrease in density As a result, the warmer, less dense portion of the fluid will tend to rise through the surrounding cooler fluid. Convection can occur in liquids or gases The clouds we see in the atmosphere are often the result of convection. 1. Sunlight heats the surface. The warm surface then heats the atmosphere in contact with it via conduction. 2. The warm air in contact with the surface is less dense and rises, while cooler air sinks. This process transports energy via convection. 3. As the warm air rises, it cools, and (depending on the water content of the atmosphere) a cloud may form.

Conduction

-occurs when energy is passed directly from one item to another. -If you stirred a pan of soup on the stove with a metal spoon, the spoon will heat up through conduction. -Metals are excellent conductors of heat energy. Wood or plastics are not. These "bad" conductors are called INSULATORS. That's why a pan is usually made of metal while the handle is made of wood or strong plastic. Conduction can occur in solids, liquids, or gases. However, because the molecules in gases are far apart, gases are much poorer conductors than either solids or liquids.

Wavelengths

-the distance from one crest to the next -Shorter wavelength = higher energy -All types travel at 300,000 km/sec or 186,000 miles/sec

"Rules" of Radiation

1.All things with a temperature above absolute zero emit radiation -Sun emits energy -Earth emits energy -YOU emit energy -EVERYTHING emits energy... - Unless it's at "absolute zero" when molecules stop moving 2. The higher the temperature of the object, the shorter the wavelength of radiation emitted 3. The higher the temperature of the object, the greater the total radiation emitted Sun is 6000 K (10,000 F) Earth is 289 K (59 F) Sun 160,000 times more energy than the Earth This concept is called the Stephan-Boltzman Law

Radiation emitted by the Earth

Earth emits radiation at longer wavelengths than the sun. -Emits considerably less radiant energy than the sun -Over 95% of the Earth's radiation has wavelengths between 2.5 and 30 micrometers (Infrared) NOTE: Earth emits most of its energy in the infrared portion of the spectrum Earth does not EMIT any energy in the visible portion of the spectrum

Energy and Phase Changes

Heat is ABSORBED from the environment Solid to Liquid: Melting Liquid to Gas: Evaporation (COOLING Process) Solid to Gas: Sublimation Heat is RELEASED into the environment Gas to Liquid: Condensation Liquid to Solid: Freezing (WARMING Process) Gas to Solid: Deposition

Record Temperatures

Highest temperature ever recorded 56.7 °C (134.0 °F) Death Valley, California, USA (1913 A very warm summer day in the U.S. 38 °C (100 °F) Average room temperature 20 °C (68 °F) A very cold winter day in the U.S. -18 °C (0 °F) Lowest temperature ever recorded −89.2 °C (−128.6 °F) Vostok Station, Antarctica (July 1983)

The electromagnetic spectrum of our Sun

NOTE: The peak of the Sun's energy is in VISIBLE light

There are three ways by which heat is transferred:

Radiation Conduction Convection

Absorbed

Solar energy that isn't reflected or scattered can be absorbed. Solar energy isn't absorbed equally in the atmosphere. Very short wavelengths of energy are absorbed high in the atmosphere. Most of the energy absorbed at the surface is in visible and longer wavelengths.

Hurricanes

The energy for hurricanes comes from the evaporation of warm ocean water. When this water vapor condenses into clouds in the atmosphere, a tremendous amount of energy is released in the form of latent heat.

Kinetic Energy

The energy within a body that is a result of its motion. KE=1/2mv^2 The particles will not all have the same energy, and the energy of the particles is constantly changing as they undergo changes in speed So, for a given sample of matter, we can only talk about the average kinetic energy of the particles.

Latent Heat

The heat energy required to change a substance from one state to another. Example -Water from solid to liquid -temperature stays constant -Heat is used to MELT the ice does not produce a temperature change

But what do we really mean by "temperature"?

The particles (atoms and molecules) that make up all substances are always in motion We call this energy of motion "kinetic energy"

Temperature Scales

The two temperature scales that you are most likely to see in everyday life are the Fahrenheit and Celsius scales. The Kelvin scale is mostly used in the sciences. The Fahrenheit scale was used in most English speaking countries until the 1960s, when most countries switched to Celsius as part of a process to standardize units of measure to the metric system. Today, the United States, Belize, Palau, Guam, Puerto Rico, and the U.S. Virgin Islands are the primary users of the Fahrenheit temperature scale.

The Electromagnetic Spectrum

Visible light is a very small portion of the electromagnetic spectrum

Temperature

is a measure of the average kinetic energy of the particles in a substance. When we refer to an object as being hot, we mean it has high temperature Temperature is more easily measured and defined than heat content

Absolute Zero

molecules stop moving, no thermal motion.

Radiation

the process by which heat is transferred in wave form at the speed of light -Travels through the vacuum of space -We can feel heat transferred by radiation, even though we are not in direct contact with the hot substance -sunlight energy reaches Earth via radiation - radiation is also the way energy leaves Earth to return to space

0 K

the temperature at which all molecular motion is presumed to cease

Heat

the transfer of energy into or out of an object due to the temperature differences between the objects After heat is transferred it is stored as internal energy - the total amount of energy stored in the particles of an object. When an object is heated up, its particles gain more kinetic energy and hence its internal energy increase. Heat content is a measure of the total molecular energy of a substance. The heat content of an object depends on three characteristics of a substance: its temperature, its mass, and its composition