Britannica Educational Publishing - Matter

MATTER

INTRODUCTION TO PHYSICS

EDITED BY ANDREA R. FIELD

Published in 2013 by Britannica Educational Publishing
(a trademark of Encyclopdia Britannica, Inc.)
in association with Rosen Educational Services, LLC
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First Edition

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Library of Congress Cataloging-in-Publication Data

Matter/edited by Andrea R. Field.1st ed.
p. cm.(Introduction to physics)
In association with Britannica Educational Publishing, Rosen Educational Services.
Includes bibliographical references and index.
ISBN 978-1-61530-842-2 (eBook)
1. MatterJuvenile literature. I. Field, Andrea R.
QC173.16.M375 2013
530dc23

2011052216

Cover, p. 3 (molecule) Chepe Nicoli/Shutterstock.com; cover (equation) EtiAmmos/Shutterstock.com; pp. iStockphoto.com/Baris Simsek; remaining interior background images iStockphoto.com/Duncan Walker

W hen dealing with physics, the answer to the question Whats the matter? has to be a resounding Everything! The stars in the night sky, rocks found buried deep beneath Earths surface, all creatures great and small (including humans)everything and anything you can think of is composed of matter. This book takes that rather general statement and adds the details that explain the existence of matter, its properties, and, at the risk of stating the obvious, why matter matters.

At the microscopic level, matter is made up of atoms, molecules, and ions. Close to 100 different types of atomsthe smallest pieces of matterexist in nature. Molecules are combinations of atoms, while ions are single or grouped atoms that have an electrical charge. Clustered in the center of each atom are protons and neutrons, around which particles called electrons orbit.

There are three different forms, or phases, of matter: solid, liquid, and gas. Solid matter has a definite size and shape that does not change. The volume of liquids is definite, but their shape is determined by the container they occupy. Gases do not have a definite size or shape; they simply expand to fill a container completely. The phases of matter can change. One example is solid ice melting into liquid water; refreeze the water and you have a phase change in reverse.

Another characteristic of matter is that it is subject to inertia and gravitation. Inertia describes matters resistance to stopping when it is moving and its resistance to moving when it is at rest. The more mass an object hasmeaning the more matter the object is composed ofthe greater the resistance. In other words, the more massive something is, the greater the force required to get it to move or stop moving.

Mass is not as important as weight when it comes to gravitation, or gravity, which is the force that attracts, or draws, all forms of matter to each other. On Earth, gravity pulls all objects toward the planets core. An objects distance from the core determines the strength of this pull. Gravity, not mass, is what gives matter weight. For example, an object experiences a stronger gravitational pull at Earths surface than it does at the top of a mountain. The strength of the pull, in turn, determines the objects weight. Thus, the object weighs more at the surface than it does atop the mountain, even though its mass has not changed.

Physicist John Daltons table of elements, fronted by one of his diagrams of atoms and three atomic models. Science and Society Picture Library/Getty Images

Peoples understanding of matter has grown over the years. For centuries scientists were sure that matter and energy were two separate things. Yet, as Albert Einstein proved with his theory of special relativity (better known as E=mc2), the two are so closely linked that they are said to be equivalent. In fact, matter can be converted to energy, and energy can be converted to matter.

Beyond special relativity, there have been other theories of matter raised in the modern era. The rise of quantum mechanics (the study of matter at the atomic and smaller levels), astronomical observations, and experimentation in particle physics each have revealed plenty about the nature of matter. No doubt more theories will come in the future as scientists continue to investigate the fundamental topic of matter.

A n electron, a grain of sand, an elephant, and a giant star at the edge of the visible universe all have one thing in commonthey are composed of matter, which is the material substance that makes up the physical universe. A beam of light, the motion of a falling stone, and the explosion of a stick of dynamite also have one thing in commonthey are expressions of energy. Together, energy and matter form the basis for all observable phenomena.

Matter is made up of tiny units known as atoms, molecules, and ions. Atoms are the basic building blocks of chemistry. An atom is the smallest piece of matter that has the characteristic properties of a chemical element, such as hydrogen, oxygen, calcium, iron, gold, and neon. More than 90 types of atoms exist in nature, and each one forms a different element. Though elements are made up of only one type of atomgold contains only gold atoms, and neon contains only neon atomsother substances are mixtures of different kinds of atoms. Atoms also join together chemically to form molecules. Ions are electrically charged atoms or groups of atoms. All atoms are roughly the same size. About 50 million atoms of solid matter lined up in a row would measure only 0.4 inch (1 centimeter).