hen dealing with physics the answer to the question What s the matter has to be a resound ing Everything The stars in the night sky rocks found buried deep beneath Earth s sur face 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 mat ter 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 atoms the smallest pieces of matter exist in nature Molecules are combinations of atoms while ions are sin gle or grouped atoms that have an electrical charge Clustered in the center of each atom are protons and neutrons around which par ticles 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
INTRODUCTION or shape they simply expand to fill a con tainer 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 matter s resistance to stopping when it is moving and its resistance to mov ing when it is at rest The more mass an object has meaning the more matter the object is composed of the 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 planet's core An object s 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 Earth's surface than it does at the top of a mountain The strength of the pull in turn determines the object s weight Thus I
INTRODUCTION the object weighs more at the surface than it does atop the mountain even though its mass has not changed People s understanding of matter has grown over the years For centuries scien tists were sure that matter and energy were two separate things Yet as Albert Einstein proved with his theory of special relativ ity better known as E mc 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 mechan ics 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 mat ter No doubt more theories will come in the I future as scientists continue to investigate the fundamental topic of matter
