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Physics and Early Theories Help

By — McGraw-Hill Professional
Updated on Sep 5, 2011

Introduction to Physics and Early Theories

The idea that matter exists in the form of particles, rather than as a continuous mass, is many centuries old. How do we explain the fact that some substances are more dense than others, that some retain their shape while others flow freely, and that some are visible while others are not? The many ways in which matter can exist are difficult to explain in any other way than by means of a particle theory . This was the reasoning ancient alchemists used when they hypothesized that matter is comprised of tiny, invisible particles, or atoms .

All atoms are made up of countless smaller particles whizzing around. These subatomic particles are dense, but matter is mostly empty space. Matter seems solid and continuous because the particles are so small that we can’t see them, and they move so fast that their individual motions would appear as a blur even if the particles themselves could be seen. However, the spaces within atoms are vastly greater than the particles that comprise them. If we could shrink ourselves down to the subatomic scale and also slow down time in proportion, a piece of metal would look something like a huge, hysterical swarm of gnats. Did the first chemical and physical scientists realize that the atoms they had dreamed up actually consisted of smaller particles, that these particles in turn consisted of tinier ones still, and that some people in future generations would come to believe that the particle sequence extends down to smaller and smaller scales ad infinitum?

The Smallest Piece

Millennia ago, scientists deduced the particle nature of matter from observing such things as water, rocks, and metals. These substances are much different from each other. However, any given material—copper, for example—is the same wherever it is found. Even without doing any complicated experiments, early physicists believed that substances could only have these consistent behaviors if they were made of unique types, or arrangements, of particles.

It was a long time before people began to realize how complicated this business really is. Even today, there are plenty of things that scientists don’t know. For example, is there a smallest possible material particle? Or do particles keep on getting tinier as we deploy more and more powerful instruments to probe the depths of inner space? Either notion is difficult to comprehended intuitively. If there is something that represents the smallest possible particle, why can’t it be cut in half? However, if particles can be cut into pieces forever and ever, then what is the ultimate elementary particle? A geometric point of zero volume? What would be the density of such a thing? Some mass divided by zero? This doesn’t make sense! A literal and conclusive answer to this puzzle remains to be found. We may never know all there is to know about matter. It may not even be possible to know everything about matter.

The Elements

Until about the year 1900, there were respected people who refused to believe the atomic theory of matter. Today, however, practically everyone accepts it. The atomic theory explains the behavior of matter better than any other scheme. Some people still think that matter is continuous; a few folks still believe that our planet Earth is flat, too.

Eventually, scientists identified 92 different kinds of fundamental substances in nature and called them elements . Later, more elements were made artificially. This process of discovery is still going on. Using machines known as particle accelerators , sometimes called atom smashers , nuclear physicists have fabricated human-made elements that can’t exist in nature, at least not under conditions resembling anything we would imagine as normal.

Every Element Is Unique

Atoms of different elements are always different. The slightest change in an atom can make a tremendous difference in its behavior. You can live by breathing pure oxygen but you cannot live off of pure nitrogen. Oxygen will cause metal to corrode, but nitrogen will not. Wood will burn furiously in an atmosphere of pure oxygen but will not even ignite in pure nitrogen. However, both look, smell, and feel exactly the same at normal temperature and pressure. Both are invisible gases, both are colorless, both are odorless, and both are just about equally heavy. These substances are so different because oxygen and nitrogen consist of different numbers of otherwise identical particles.

There are many other examples in nature where a tiny change in atomic structure makes a major difference in the way a substance behaves.

Practice problems of these concepts can be found at: Particles of Matter Practice Test

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