Rubber is one of our most interesting and most important raw materials. Natural rubber comes from the juice of a tree. Synthetic rubber is manufactured from chemicals.
Rubber is especially useful for several reasons. It holds air, keeps out moisture, and does not readily conduct electricity. But its chief importance to us is that it is elastic. When you stretch a rubber band and let it go, its elasticity makes it quickly spring back to its original shape. A rubber ball bounces because of this same springiness. Your rubber heels absorb shock when you walk because they have elasticity.
We depend so much on rubber that it would be almost impossible to get along without it. This is not the case with most other materials. If we lack one material, we can usually substitute another. A house can be built using such materials as wood, brick, stone, concrete, glass, or metal. Clothes can be made of cotton, silk, wool, or other fibers.
But what about the tires of an automobile, truck, or bus? It is hard to imagine making them of anything but rubber. Only rubber is elastic, airtight, water-resistant, shock-absorbing, and long-wearing.
Manufacturers make between 40,000 and 50,000 rubber products. A typical automobile has about 600 rubber parts. Some cars, of course, use less rubber than this, and some use more. Many trucks and buses even have springs made of rubber instead of steel.
