You know that friction also causes heat. Think about when you rub your hands together. It is friction that makes them warm. But why does this happen? Friction causes the molecules on rubbing surfaces to move faster. Faster moving particles have more heat energy. Heat from friction can be useful. Can you think of other places where you might find friction? Friction also lets you light a match. Heat from friction can also cause problems. It can cause a car to overheat. To reduce friction, oil is added to the engine. Oil coats the surfaces of moving parts. This coating of oil makes them slippery. When things are slippery there is less friction. Have you ever seen a sign that says, slippery when wet? This too has to do with friction. Water, like oil, can reduce friction. The wet surface may allow your shoes to slide more easily.

Are you likely to experience more friction walking on a surface covered in oil or water than on a dry surface?

Befitting a lush, tropical island stranded in the middle of the ocean, Madeira's origins are shrouded in mystery and fanciful legend. Some claim that the archipelago is what remains of Plato's lost Atlantis, or part of a landmass that once fused the continents of Europe and America. The Portuguese Step Ashore: Recorded history of the volcanic archipelago begins in relatively recent times: 1418, just as the golden age of Portuguese discovery was erupting. Under the leadership of Henry the Navigator, caravels set out from the westernmost point of the Algarve, in southern Portugal, in search of foreign lands, fame, and wealth. Joao Goncalves Zarco, sailing in the service of Prince Henry, made the first of many famous Portuguese discoveries, which would culminate a century later in Magellan's historic circumnavigation of the globe. Zarco happened upon a small volcanic archipelago 1,000 km from Lisbon. Perhaps Zarco knew precisely where he was heading, having learned of the existence of Madeira from a Castilian source. After all, the waters of the Canary Islands, only 445 km (275 miles) to the south, had occupied busy shipping lanes for very nearly a century, and Genovese maps from the mid-14th century depict both Madeira and Porto Santo. More likely, Zarco was heading for Guinea and storms forced him onto the beach of Porto Santo. If so, then he was extremely fortunate, for he managed to land on the only large, sandy beach for hundreds of miles around. Little wonder he subsequently named it Porto Santo (Holy Port). The following year Zarco returned to claim the larger island he had seen from Porto Santo, and with him went Tristao Vaz Teixeira and Bartolomeu Perestrelo. They officially became the first men to set foot on the heavily forested island, naming it Ilha da Madeira, "Island of Timber. " The Portuguese Crown, delighted with its first important discovery, immediately embarked on a program of colonization. Zarco and Teixeira were appointed co-governors of Madeira, while Perestrelo was awarded Porto Santo.

Officially, Zarco, Perestrelo, and what other man were the first three men to set foot on Ilha da Madeira?

Tuesday, September 11, 2001, dawned temperate and nearly cloudless in the eastern United States. Millions of men and women readied themselves for work. Some made their way to the Twin Towers, the signature structures of the World Trade Center complex in New York City. Others went to Arlington, Virginia, to the Pentagon. Across the Potomac River, the United States Congress was back in session. At the other end of Pennsylvania Avenue, people began to line up for a White House tour. In Sarasota, Florida, President George W. Bush went for an early morning run. For those heading to an airport, weather conditions could not have been better for a safe and pleasant journey. Among the travelers were Mohamed Atta and Abdul Aziz al Omari, who arrived at the airport in Portland, Maine. Boston: American 11 and United 175. Atta and Omari boarded a 6:00 A.M. flight from Portland to Boston's Logan International Airport. When he checked in for his flight to Boston, Atta was selected by a computerized prescreening system known as CAPPS (Computer Assisted Passenger Prescreening System), created to identify passengers who should be subject to special security measures. Under security rules in place at the time, the only consequence of Atta's selection by CAPPS was that his checked bags were held off the plane until it was confirmed that he had boarded the aircraft. This did not hinder Atta's plans. Atta and Omari arrived in Boston at 6:45. Seven minutes later, Atta apparently took a call from Marwan al Shehhi, a longtime colleague who was at another terminal at Logan Airport. They spoke for three minutes. It would be their final conversation.
What were the security rules for CAPPS prescreening system on September 11, 2001?