AEROGRAPHER'S MATE 3 & 2 



without forming new compounds. Their atoms 

 do not combine. This is known as a mixture. 

 Air is a familiar mixture. Every sample of air 

 contains several kinds of molecules which are 

 chiefly molecules of the elements oxygen, 

 nitrogen, and argon, together with the com- 

 pounds of water vapor and carbon dioxide. 

 Ocean water, too, is another mixture, made 

 up chiefly of water and salt molecules, with 

 a smaller number of molecules of many other 

 compounds as well as molecules of several 

 elements. 



STATES 



Matter is found in one or more of the 

 following three states: 



1. Solid. Solids are substances which have 

 a definite volume and shape and will retain 

 their original shape and volume after being 

 moved from one container to another: An ex- 

 ample is a block of wood or a bar of metal. 



2. Liquid. A liquid has a definite volume, 

 because it is almost impossible to pack it into 

 a smaller space. However, when a liquid is 

 moved from one container to another, it will 

 retain its original volume, but will take on the 

 shape of the container into which it is moved. 

 For example, if a glass of water is poured 

 into a larger bucket or pail, the volume remains 

 unchanged but the liquid will occupy a different 

 space in that it conforms to the walls of the 

 container in which it is poured. 



3. Gas. Gases have neither a definite shape 

 nor a definite volume. They will not only take 

 on the shape of the container into which they 

 are placed but will expand and fill it, no matter 

 what the volume of the container. 



Since gases and liquids flow easily, they are 

 both called fluids. Moreover, many of the laws 

 of physics which apply to liquids apply equally 

 as well to gases. 



PHYSICAL PROPERTIES OF 

 METEOROLOGICAL SIGNIFICANCE 



From our definition of matter (anything that 

 occupies space and has weight), it can be said 

 that all kinds of matter have certain properties 

 in common. These properties are inertia, mass, 

 gravitation, weight, volume, and density. These 

 properties are covered briefly in this section 

 and are called the general properties of matter. 



Inertia 



This property of matter is perhaps the most 

 fundamental of all attributes of matter. In 

 short, it is the tendency for an object to stay 

 at rest if it is in a position of rest, or to 

 continue in motion if it is moving. Inertia makes 

 bodies hard to start and hard to stop. 



Mass 



Mass is the quantity of matter contained 

 in a substance. This property does not vary 

 unless matter is added to or subtracted from 

 the substance. For example, a sponge can be 

 compressed or allowed to expand back to its 

 original shape and size, but the mass does not 

 change. The mass will remain the same on 

 the earth as on the sun or moon, or at the 

 bottom of a valley or the top of a mountain. 

 Only if something is taken away or added to 

 it is the mass changed. Later in the chapter 

 its meaning will have a slightly different 

 connotation. 



Gravitation 



Every body attracts or pulls upon other 

 bodies. In other words, all matter has gravi- 

 tation. One of Newton's laws states that the 

 force of attraction between two bodies is 

 directly proportional to the product of their 

 masses and inversely proportional to the square 

 of the distance between their two centers. 

 Therefore, a mass will have less gravitational 

 pull on it at the top of a mountain than it would 

 at sea level because the center is displaced 

 farther away from the gravitational pull of the 

 center of the earth. However, the mass remains 

 the same even though the gravitational pull is 

 different. Gravity also varies with latitude, 

 being slightly less at the Equator than at the 

 poles due to a greater distance from the center 

 of the earth. 



Weight 



The weight of an object is a measure of 

 gravitational attraction and depends upon the 

 mass or quantity that it contains and the 

 amount of gravitational attraction the earth has 

 for it. Weight is a force, and as such it should 

 be expressed in units of force. 



258 



