UNIT 2—LESSON 4
OVERVIEW Describe the adiabatic
process and determine how stability and instability affect the atmosphere.
OUTLINE First Law of Thermodynamics Adiabatic process Stability and Instabiliy ATMOSPHERIC ENERGY There are two basic kinds of atmospheric
First Law of Thermodynamics
Stability and Instabiliy
There are two basic kinds of atmosphericenergy important to AGs—kinetic and potential. Kinetic energy is energy that performs work due to present motion while potential energy is energy that is stored for later action. Kinetic energy is discussed first in relation to its effect on the behavior of gases.
According to the kinetic theory of gases, discussed in Lesson 2-3, the temperature of a gas is dependent upon the rate at which the molecules are moving about and is proportional to the kinetic energy of the moving molecules. The kinetic energy of the moving molecules of a gas is the internal energy of the gas; it follows that an increase in temperature is accompanied by an increase in the internal energy of the gas.
Likewise, an increase in the internal energy results in an increase in the temperature of the gas. This relationship, between heat and energy, is called thermodynamics.
An increase in the temperature of a gas or in its internal energy can be produced by the addition of heat or by performing work on the gas. A combination of these can also produce an increase in temperature or internal energy. This is in accordance with the first law of thermodynamics.
Learning Objective: Describe the adiabaticprocess and determine how stability and instability affect the atmosphere.
FIRST LAW OF THERMODYNAMICS
This law states that the quantity of energysupplied to any system in the form of heat is equal to work done by the system plus the change in internal energy of the system. In the application of the first law of thermodynamics to a gas, it may be said that the two main forms of energy are internal energy and work energy. Internal energy is manifested as sensible heat or simply tempera-ture.
Work energy is manifested as pressurechanges in the gas. In other words, work is required to increase the pressure of a gas and work is done by the gas when the pressure diminishes. It follows that if internal energy (heat) is added to a simple gas, this energy must show up as an increase in either tem-perature or pressure, or both. Also, if work is performed on the gas, the work energy must show up as an increase in either pres-sure or temperature, or both.
An example of the thermodynamic process isa manual tire pump. The pump is a cylinder enclosed by a piston. In accordance with the first law of thermodynamics, any increase in the pressure exerted by the piston as you push down on the handle results in work being done on the air. As a consequence, either the temperature and pressure must be increased or the heat equivalent of this work must be transmitted to the surround-ing bodies. In the case of a tire pump, the work done by the force on the piston is changed into an increase in the temperature and the pressure of the air. It also results in some increase in the temperature of the surrounding body by conduction.
If the surrounding body is considered to be insulated so it is not heated, there is no heat transferred. Therefore, the air must utilize this ad-ditional energy as an increase in temperature and pressure. This occurs in the adiabatic process.