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Protozoa That Cause Disease

Diseases caused by protozoan parasites are among the leading causes of death and disease in tropical and subtropical regions of the world. Developing countries within these areas contain three-quarters of the world's population, and their populations suffer the most from these diseases. Controlling parasitic diseases is a problem because there are ...

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ProtozoaThatCauseDisease
Geology

Sedimentary Rock

Sedimentary rock is one of three rock types on earth. Rock types are classified according to how the rock is formed. Igneous rock forms as it cools to a solid from molten rock. Metamorphic rock forms ... Continue reading

SedimentaryRock
Astronomy

Wernher Von Braun

Wernher Von Braun was one of the world's first and foremost rocket engineers and a leading authority on space travel. His will to expand man's knowledge through the exploration of space led to the ... Continue reading

VonBraun
Biology

Yes! We Have New Bananas

Did you know that a plant disease determined what banana variety is in your market? Bananas, which originated in Africa and are now grown in every tropical region, are perhaps the most popular fruit ... Continue reading

YesWeHaveNewBananas
Medicine

Civets Lesson

Recently a Chinese television producer fell ill with Severe Acute Respiratory Syndrome, better known as SARS. He is the first victim in many months, although an epidemic last year claimed nearly 8000 ... Continue reading

CivetsLesson

Big Boom

BigBoomThey sound like thunder, but they're not. They're sonic booms, concentrated blasts of sound waves created as vehicles travel faster than the speed of sound. To understand how the booms are created, look to the ocean.

On the sea, there are small ripples in the water. As a boat slowly passes through the ripples, they spread out ahead of the boat. As the boat moves faster, it breaks through the ripples more quickly, forming waves. If it goes fast enough, the waves can't spread out fast enough, and they form a wake, which is much larger than a single wave. It is formed out of all the little waves that would have spread out ahead of the boat, but couldn't, because of the boat's speed.

Now picture the same thing happening in the air. Instead of a boat, there is an airplane moving through the sky. When a plane travels through the air, it produces sound waves. You can't see sound waves like you can see waves of water, but they're still there. If the plane is traveling slower than the speed of sound, then sound waves can spread out ahead of the plane. If it breaks the sound barrier and flies faster than the speed of sound, it produces a sonic boom when it flies past. The boom is the wake of the plane's sound waves. All the sound waves that would have normally spread out ahead of the plane are combined together, and you hear the boom.