A roller coaster works the same way as a bicycle coasting down a hill. When you ride your bike to the top of a hill, you pedal to get there. Then, to coast down the hill, you take your feet off the pedals and glide down the other side. If the slope is steep enough, you can go very fast. Similarly, a roller coaster is only powered at the beginning of the ride, when the coaster, or train, is pulled up the first hill. When it goes over the top of the hill, the weight of the train itself, pulled downward by gravity, is what keeps the entire unit moving.
There are no cables that pull the train around the track. This conversion of potential energy (stored energy) to kinetic energy (the energy of motion) is What drives the roller coaster, which often reaches 60 miles (96.5 kilometers) per hour. Running wheels guide the train on the track, and friction wheels control the train’s movement to either side of the track. A final set of wheels keeps the train on the track even if it is upside down. Air brakes stop the car as the ride ends.
The fastest growing hairs on the human body are men’s beard hairs. If the average male never trimmed his beard, it would grow to almost 30 feet (9 meters) long in his lifetime.
“Dog days” are the hot, humid days of summer that usually take place in the Northern Hemisphere in July and August typically between July 3 and August 11. The days get their name from the dog star Sirius of the constellation Canis Major.
At this time of year, Sirius, the brightest visible star, rises in the east at the same time as the Sun in the northern hemisphere. Ancient Egyptians believed that the heat of this brilliant star added to the Sun’s heat to create this hot weather and they blamed the star for everything from withering droughts to sickness.
Scientists don’t really know why we cry when we’re unhappy or hurt (or sometimes, even joyful). But tears help express deeply felt emotions and often release stress and tension from the body. From our earliest days, when we were babies and could not yet communicate through language, crying let the people around us know that we needed something.
Frequently, even after we become older, crying still serves as a wordless signal that something help or comfort is needed. In places all over the world, no matter what language is spoken, crying expresses emotions that are easily understood by all.