Chapter 2 Atmospheric Physics

CHAPTER 2 ATMOSPHERIC PHYSICS The science of physics is devoted to finding, defining, and reaching solutions to problems. It is the basic science that deals with motion, force, and energy. Physics, therefore, not only breeds curiosity of one’s environment, but it provides a means of acquiring answers to questions that continue to arise. Atmospheric physics is a branch of physical meteorology that deals with a combination of dynamic and thermodynamic processes that account for the existence of numerous atmospheric conditions. To understand the weather elements and to analyze meteorological situations you must know how to apply the fundamental principles of physics. This does not mean that you must be able to understand all of the complicated theories of meteorology. It does mean, however, that you should have a working knowledge of elementary physics. You should learn how to apply the rules of physics to understand how the atmosphere works. This is necessary to perform your duties as an Aerographer’s Mate in a creditable manner. MOTION LEARNING OBJECTIVE: Describe the laws of motion and determine how motion is affected by external forces. Any general discussion of the principles of physics must contain some consideration of the way in which mass, force, and motion are related. In physics, the laws of motion state that an object at rest never starts to move by itself; a push or a pull must be exerted on it by some other object. This also applies to weather. Weather has complex motions in the vertical and horizontal planes. To fully understand how and why weather moves, you must have a basic knowledge of motion and those external forces that affect motion. TERMS In dealing with motion several terms should be defined before you venture into the study of motion. These terms are inertia, speed, direction, velocity, and acceleration. Inertia An object at rest never moves unless something or someone moves it. This is a property of all forms of matter (solid, liquid, or gas). Inertia, therefore, is the property of matter to resist any change in its state of rest or motion. Speed Speed is the rate at which something moves in a given amount of time. In meteorology, speed is the term that is used when only the rate of movement is meant. If the rate of movement of a hurricane is 15 knots, we say its speed is 15 knots per hour. Direction Direction is the line along which something moves or lies. In meteorology, we speak of direction as toward or the direction from which an object is moving. For example, northerly winds are winds COMING FROM the north. Velocity Velocity describes both the rate at which a body moves and the direction in which it is traveling. If the hurricane, with its speed of 15 knots per hour, is described as moving westward, it now has velocity—both a rate and direction of movement. Acceleration This term applies to a rate of change of the speed and/or the velocity of matter with time. If a hurricane, which is presently moving at 15 knots, is moving at 18 knots 1 hour from now and 21 knots 2 hours from now, it is said to be accelerating at a rate of 3 knots per hour. LAWS OF MOTION Everything around us is in motion. Even a body supposedly at rest on the surface of Earth is in motion because the body is actually moving with the rotation of Earth; Earth, in turn, is turning in its orbit around the Sun. Therefore, the terms rest and motion are relative 2-1