Pertanyaan

Tornados occur when the conditions that cause thunderstorms are unusually violent. Winds blow in opposite directions around a strong updraft start a narrow, violent whirl. Centrifugal force effectively throws the air away from the center, leaving a core of very low pressure. This is much like stirring water in a cup, thus forming a vortex-like dip in the surface. This low-pressure core acts as a partial vacuum, sometimes helping to lift the roofs off houses. Most of the damage, though, results from the force of the wind itself. Around the edges of the whirl, wind speeds may reach 300 miles (480 kilometers) per hour. At first, the tornado’s funnel is whitish-gray because it is composed of minute water droplets formed as the air in the funnel expands and cools. After touching down, the funnel becomes dark because of all of the debris it has picked up. This debris can include soil, tree limbs, and parts of buildings; tornados have been known to pick up automobiles, horses, and whole trees. . A tornado usually moves toward the east (or often northeast in the Northern Hemisphere and southeast Hemisphere) at 25 to 40 miles (40 to 65 kilometers) per hour. Fortunately, most tornados are less than half a mile (800 meters) wide; the edge of one may destroy all of the houses on one side of a street while leaving those on the other side completely undamaged. Deaths from tornados in the United States averaged roughly 100 per year over the last century. However, they have dropped somewhat in recent decades as better forecasting and warning systems have been implemented. Why have deaths from Tornado in the United States decreased in the recent decades?