Energy
Energy is the ability to do work, and work results when a force causes displacement or movement. Combining these concepts, we can say that energy is the ability to move “stuff.” It is the essence that drives a planet’s processes – actually, all processes in the universe. No biggie. Nothing would ever move or change without it, and life would not exist since all forms of life need energy.
Waves get their kinetic and potential energy from the kinetic energy of the wind.
But luckily, we do have energy in the universe. On Earth, the Sun provides relatively consistent radiation that drives many of our surface processes.
Energy flows are the transformation of energy from one form to another. For example, we eat food that has chemical energy. Our body changes the chemical energy into a variety of types:
- Kinetic energy (from walking to pumping blood through the body),
- Electrical energy (which allows us to think and coordinate and process sensory information and muscle movement), and
- Thermal energy (we maintain near-constant body temperature despite constantly losing energy – thermal energy, radiation, and sound – to our surroundings).
Energy cannot be created or destroyed; it just changes from form to form.
Main Types of Energy
Potential Energy: an object’s stored energy based on its position relative to others, stresses within itself, its electric charge, or other factors. Common types of potential energy are gravitational energy, electric energy, magnetic energy, elastic energy, chemical energy, and nuclear energy.
Kinetic Energy: an object’s energy due to its motion. Common types of kinetic energy are thermal energy, sound energy, and electromagnetic radiation.
Our approach in Earth systems focuses on how energy creates and sustains the matter cycles in which materials in various chemical forms are transported around the globe. The matter cycles and energy flows sustain the dynamic life webs found on Earth.
Connections between Energy and Matter
Matter is anything that consists of atoms and molecules. An atom is the fundamental component of matter since it cannot be broken down by any chemical process. Molecules are two or more atoms that are chemically bonded to each other by intramolecular forces, so in a sense, the bonds are within the molecule. Separate molecules may also bond with each other to form a solid or liquid by weaker intermolecular forces where the bonds are between two or more molecules. Intramolecular bonds influence the molecule’s chemical properties, while intermolecular bonds determine its physical properties.
Energy and the Phase of Matter
All matter is moving, but there are constraints on how atoms and molecules move based on their phase or state. In a gas, molecules vibrate and move freely past each other. In a liquid, molecules vibrate and slide past each other since they are closer together than when a gas. Molecules in a solid vibrate about a fixed position.
What causes these constraints of motion? Intermolecular bonding! The strength of an intermolecular bond depends on the electrical attraction between the molecules (recall, opposite electrical charges attract) and inversely proportional to the square of the distance between the charges of the molecules. So the IMF increases rapidly as the molecules become closer together.
When a substance’s average energy of intermolecular attraction is greater than the average kinetic energy (read: at lower temperatures), its molecules are held tightly together to form a solid. At higher temperatures where the material’s average kinetic energy exceeds the average energy of intermolecular attraction, its molecules move freely past each other in a gaseous state. Liquids exist at temperatures between those that form a solid and those that produce gas. The two energies are similar to allow for the molecules to be held closely, but they are moving fast enough to slide past each other. Since liquids and gases flow from one place to another, they are referred to as fluids.
Above is a video illustrating the motion of molecules for the three states of matter. The video is from https://www.youtube.com/watch?v=s-KvoVzukHo.
Transfer of Thermal Energy in Earth Systems
Thermal energy is the energy contained within a system that is responsible for its temperature, which is a measure of the average kinetic energy of the atoms within a material. The primary driver of Earth’s matter cycles involves the transfer of thermal energy (known as heating) between matter with different temperatures. The fundamental heating mechanisms in Earth’s systems are conduction, radiation, advection, convection, and latent heat.
Conduction is the transfer of thermal energy through molecular collisions. If two molecules collide and they have different kinetic energies (KE), the molecule with the most KE transfers some to the particle with the least. When a region is hotter than another, the more vigorous collisions in the warmer region conduct heat toward the colder area.
Radiation is the emission and transmission of photons, which are massless packets of energy. “Light” is radiation that we see with our eyes. When an object emits a photon, it gives up energy, and when an object absorbs a photon, it gains energy. This energy may be converted to heat, but it could also be transformed into other forms. For example, during photosynthesis, radiation is converted to chemical energy in the form of intramolecular bonds.
Advection is the horizontal movement of fluids with different temperatures. Examples of this phenomenon include a cold wind from higher latitudes or the warm Gulf Stream in the Atlantic Ocean.
Convection is the vertical movement of fluids with different temperatures. In our atmosphere, convection is responsible for creating most of our clouds and precipitation.
Rarely in Earth processes does the adage “What comes up must come down” is not precisely correct. Instead, it usually goes, “What goes up must go sideways before coming down.” Convection and advection typically occur together, creating convection cells.
Latent heat is the heat required to create a phase change (solid, liquid, or gas) without change of temperature. Humans cool by secreting sweat onto our skin, which evaporates and cools the skin.
Collectively, we will refer to these five mechanisms as CRACL (Conduction, Radiation, Advection, Convection, Latent heat). Explore each process separately in the submenus of the Energy menu and then collectively in the CRACL submenu.
How CRACL Came to Be
CRACL is not a term used in the scientific community. Still, when I was finishing up heating mechanisms that drive our atmospheric motion while teaching my first high school meteorology course, one of my students looked at the board and said, “CRACL.” I found the acronym helped people remember that there is usually more than one heating process involved, and the term provided a quick checklist for what they were.
Big Ideas
- Energy is the ability to move “stuff.”
- Energy flows, meaning it transforms from one form to another.
- Thermal energy is the energy contained within a system that is responsible for its temperature.
- Temperature is a measure of the average kinetic energy of the atoms within a material.
- Heating is the transfer of thermal energy between matter with different temperatures.
- There are five primary heating mechanisms in Earth’s systems, and collectively these processes will be referred to as “CRACL” in the Science Pickle website:
- Conduction
- Radiation
- Advection
- Convection
- Latent Heat
Explore the heat transfer mechanisms separately:
Or explore how they work together: CRACL.
Next, after exploring Energy topics above: Sun-Earth Connection
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