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General Properties of Matter

Suppose you received a gift and wanted to tell your friend about it. Only, you wanted to describe the gift without actually naming the object. What are some of the characteristics you would use?

You might start with the size and shape of the object. Next, you might describe how the object feels to your touch. Is it soft, hard, spongy, or fluffy? Is it smooth or rough? Is it solid or hollow? If it is hollow, does it contain other objects? Would the object float, sink, or perhaps even swim in water?

The words you use to describe the object are its characteristics. All objects have certain characteristics that help you identify them. And although most of the objects around you have different characteristics, they share one important quality. They are all forms of matter. Matter is what the world is made of. All objects consist of matter.

Figure 3-1 What characteristics would you use to describe this sunset?

Your senses of smell, sight, taste, and touch help you become familiar with the variety of matter that surrounds you. Some kinds of matter are easily recognized. Plants, animals, rocks, soil, water, salt, and silver are examples of matter that are easily observed. Less easily observed, but still matter, are oxygen, carbon dioxide, nitrogen, ammonia, and air. Are these different kinds of matter similar in some ways? Is glass anything like ammonia? Do silver and oxygen have anything in common?

In order to answer these questions, you must know something about the properties, or characteristics, of matter. Properties describe an object. Color, odor, shape, texture, and hardness are properties of matter. They are very specific properties of matter, however. Specific properties make it easy to tell one kind of matter from another.

Some properties of matter are more general. Instead of describing the differences between forms of matter, general properties describe how all matter is the same. General properties of matter include mass, weight, volume, and density.

MASS

The most important general property of matter is that it has mass. Mass is the amount of matter in an object. The mass of an object is constant. It does not change unless some matter is added to the object or removed from the object. This means that the mass of an object does not change when you move the object from one location to another.

Scientists define mass in another way. Mass is the measure of the inertia of an object. Inertia is the resistance of an object to changes in its motion. Objects that have mass resist changes in their motion.

The more mass an object has, the greater is its inertia. The force that must be exerted to overcome that inertia is also greater. Which would be harder to pull up a hill, an empty wagon or a wagon occupied by two of your friends?

Mass is measured in units called grams (g) and kilograms (kg). One kilogram is equal to 1000 grams. The mass of small objects is usually expressed in grams. A nickel, for example, has a mass of about 5 grams. The mass of this book is about 1700 grams, or 1.7 kilograms. The estimated mass of the sun in kilograms is 2 followed by 30 zeros.

Mass is measured on an instrument called a balance. The mass of an object is determined by comparing its mass on the balance to the known masses of standard objects.

WEIGHT

Another general property of matter is weight. An object has weight because it has mass. Weight is the response of mass to the pull of gravity.

Figure 3.2 This is a scale used for measuring weight.

The force of attraction between objects is called gravity. You probably have noticed that a ball thrown up in the air soon falls to the ground. And you know that an apple that drops off a tree falls down, not up. The ball and the apple fall to the earth because of gravity, the earth's force of attraction for all objects.

All objects exert a gravitational attraction on other objects. Gravity is not a property of the earth alone. Your two hands attract each other, and you are attracted to books, chairs, and trees. But you are not pulled toward these objects as you are toward the earth because the attraction in these cases is too weak for you to notice it.

The earth's gravity is greater because the earth has a large mass. The greater the mass of an object, the greater its gravitational force.

Sharpen Your Skills Demonstrating Inertia You can demonstrate that objects at rest tend to remain at rest by using a drinking glass, playing card, and coin. 1. Place the glass on a table. 2. Lay a flat playing card on top of the glass. Place the coin in the center of the card. 3. Using either a flicking motion or a pulling motion of your fingers, quickly remove the card so it flies out from under the coin. Can you remove the card fast enough so the coin lands in the glass? You might need to practice a few times.

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