3.1: Introduction
- Page ID
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)What is Energy? You may hear frequently about “green energy”, “clean energy”, “renewable energy”, and “solar energy” in the media, as energy is currently a hot topic. Power plants, wind turbines, and solar panels may come to mind. The first paragraph in Roland Stull’s Practical Meteorology Chapter 3 discusses several types of energy right off the bat, but first of all, what is energy?
Your intuition will probably tell you that we need energy in order to do things. Energy makes stuff “go”. Your appliances, your car, and your body all need energy. Your body utilizes energy to maintain its various functions even as you read this sentence. You know that energy is a real thing that exists; you see evidence of it everywhere. The heat from your stovetop, the ice melting in your glass, and that thunderstorm rolling in are all evidence of energy at work, on scales both micro and macro.
Energy can be defined as the ability to do work. When you apply a force on an object, it is said that work is done on the object if that object is displaced, meaning it moves from its original location. For example, when you pick up a book, you exert a force against gravity causing the book to change position, and you do work on the book. The higher you lift the book or the further you throw it (should you decide to), the more work you do. However, if you apply a lot of force on a heavy piece of furniture but it doesn’t move from its original place, no work has been done regardless of the amount of effort.
\[\text { Work }=\text { Force } \times \text { displacement } \nonumber \]
\[W=F \times \Delta d \nonumber \]
\(\Delta \) is the Greek letter delta, and denotes a change. Here, \(\Delta d\) is the change in position, or the displacement. The standard unit of force is a Newton (\(N\) = kg·m·s-2), which is defined as the force required to make a mass (\(m\)) of 1 kg accelerate at 1 m·s-2. Force (\(F\)) is equal to the mass (\(m\)) of an object times its acceleration (a): \(F=m \times a .\).
Internal energy is the total amount of energy stored in any object and determines how much work the object is capable of performing. This includes both kinetic energy (energy that an object has when it is in motion) and potential energy (energy that is stored). For example, a bowling ball sitting on a table contains energy despite the fact it is not in motion. It does not have kinetic energy because it is still, but it contains potential energy simply because of where it is situated. Were it nudged off the table, the bowling ball will do work because it will be pulled downward by gravity. This is an example of gravitational potential energy. The potential energy (\(PE\)) due to gravitational pull is given by the following equation:
\[\text { Potential energy }=\text { mass } \times \text { gravitational acceleration } \times \text { height above ground } \nonumber \]
\[PE=m \times g \times h \nonumber \]
Anything that moves contains kinetic energy (\(KE\)), which is given by the following equation
\[K E=\frac{1}{2} m \times v^2 \nonumber \]
where \(m\) is the mass of an object in kilograms (kg) and v is the velocity of an object in meters per second (m·s-1). From this relationship you can see that objects with more mass or objects that are moving faster have more energy.
Energy takes on many forms and often changes forms from one to the other, but the total amount of energy in the universe remains constant. Energy cannot be created or destroyed. This means that the energy lost in a process must be the same as the energy gained in another. This is what the law of conservation of energy means, and this is what is known as the first law of thermodynamics. The first law of thermodynamics frequently comes into play in atmospheric motions and will be discussed further later in this chapter.
In short, energy is the capacity of a system to perform work. Energy is always conserved and cannot be created or destroyed. We begin this chapter with a short review of energy because energy is ultimately responsible for Earth’s weather from temperature changes in the atmosphere to the resulting air motions. Without energy, no weather would occur.