Imagine that you have been asked to find out what is inside a mysterious package without opening it. What are some things you might do to find out what is inside?
If you do not have instruments of equipment, you might begin by just looking at the package. How big is it? What is its shape? What is the outside wrapping made of ? You might pick up the package and shake it. How heavy is it? Does it rattle? Does any object inside slide around? Do you hear any particular sound? Is the package heavier at one end than at the other? Does the package have a smell? After answering all these questions you might make a guess as to what is inside.
Now suppose you are told that you may use any instruments or equipment you want to test the package. But you still may not open it. You may first want to make your earlier observations more exact. How long, wide, and high is the package? How many pounds or grams does it weight? Then you might want to test the package even more carefully. You might place a sensitive compass nearby. Is the compass affected? You could have some X- ray photographs taken of the package.
By now you might have made a long list of facts. But can you be sure what is in the package? The answer is no. Without opening it and observing directly what is inside, you cannot be absolutely certain. With the facts, you can make a better guess than you could at first. But it will still be a guess.
MATTER AROUND YOU
What are things made of? What makes them behave as they do? What makes thing change? These are some questions men have been asking for thousands of years. Some answers have been found to all these questions.
Scientist have learned that everything in the world is made of matter. Scientist know many facts about matter. They know that because of gravity, all matter has weight. They know that matter takes up space. Two pieces of matter cannot occupy the same place at the same time.
But what is matter? What makes one piece of matter different from another? Why is water wet? Why is lead heavy? Why does water become solid when it is made very cold? Why does iron become rusty? Scientists have not yet answered these questions completely. But they have learned many facts that help to explain how matter behaves and how it charges.
Early scientist spent much time observing different kinds of matter. They watched matter change. But they could not explain the differences and changes they saw.
These men crushed matter to fine powder to study it. But they found that the smallest piece of matter they could make was like the piece with which they started. A fine grain of dust from a crushed stone was still stone. It was just a smaller piece of stone. They decided that matter must be made of particles that were too small to be seen. Scientist still believe this.
Today scientists use Special microscopes to see pieces of matter much smaller than a grain of dust. But the particles that make up matter are still too small to be seen. They are hidden from man’s view because they are so small.
In spite of this, scientists are continuing to gather facts about the particles in matter. They study matter in much the same way that you might have studied the mysterious package that was discussed at the beginning of this chapter. Together, the facts they gather are called indirect evidence. Indirect evidence about the basic particles of matter is gathered by observing directly how large numbers of them behave.