Megacities
Cities have been around for thousands of years; the first ones appeared in about 3,000 BC....
A tornado is a funnel-shaped cloud. It is made up of winds that rotate at high speeds. The United States has more tornadoes than any other country in the world. About 800 tornadoes are spotted each year. Most tornadoes form between the Rocky Mountains and the Appalachian Mountains. They are usually found from Iowa, south to the Gulf of Mexico. This region is sometimes called "tornado alley." Tornadoes usually pop up at the end of spring and summer thunderstorms. They are rated on a scale from 0 to 5. If the rating is a smaller number, the speed of the wind is lower. About half of all tornadoes have winds less than 100 miles per hour. A few have winds of more than 300 miles per hour. These tornadoes can lift houses off the ground. They can even tear bark off of trees.
Cities have been around for thousands of years; the first ones appeared in about 3,000 BC....
Did you know that some foods that we think of as vegetables are really fruits? Let's t...
Many modern medicines originally came from plants. Aspirin was first made from the willow ...