题型:阅读理解 题类:常考题 难易度:普通
湖南省浏阳一中、攸县一中2016-2017学年高二下学期英语12月联考试卷
Welcome to Marksdale State Park Where fun, fitness, and education come together. Don't miss our new summer classes available during May 23- Aug 5! Swimming lessons: Ages 4—adult. Cost: $ 5 per class or $ 15 for one month. Hiking: Have a state park keeper hike through our paths with you and teach you about the park's wildlife and plants. Soccer: Our youth soccer program is unusual in that it is non-competitive. Different teams are formed every day. The focus is on each player learning to work as a team, not on one team winning it all. Boating: These classes are only for 20-year-olds and above. Fishing is only allowed with a permit. Bicycling: We have special paths built for bicyclists. Signs are posted for self-guided tours of our park. Group cycling is also available with a park guide. Paths range from easy to challenging. A message from the director: Hiking paths! Sport fields! Playgrounds! Campgrounds! Fun activities! Located on McQueeney, Marksdale State Park offers something for everyone. We have a number of plants and animals, which are in danger of dying out, being protected in our park. Sign up for one of our new summer community classes, or take a camping trip with your friends or family! Glen Harwood, Park Director |
Hot Air Balloons
| A hot air balloon is made up of 3 main parts:
The Envelope The actual fabric balloon which holds the air.
The Burner The unit which pushes the heat up into the envelope
The Basket Where the passengers and pilot stand |
The basis of how the balloon works is that warmer air rises in cooler air. This is because hot air is lighter than cool air as it has less mass per unit of volume. Mass can be defined by the measure of how much matter something contains. The actual balloon has to be large as it takes a large amount of heated air to lift it off the ground.
The burner uses propane gas to heat up the air in the envelope to move the balloon off the ground and into the air. The pilot must keep firing the burner at regular intervals throughout the flight to ensure that the balloon continues to the stable. Naturally, the hot air will not escape from the hot at the very bottom of the envelop as firstly, hot air rises and secondly, the floating power keeps it moving up.
To move the balloon upwards, the pilot opens up the propane value which lets the propane flow to the burner which in turn frees the flame up into the envelope. It works in much the same way as a gas grill: the more you open the valve, the bigger the flame to beat the air and the faster the balloon rises.
The “Parachute Valve” at the very top of the balloon is what is used to bring the balloon down towards the ground. It is a circle of fabric cut out of the top of the envelop which is controlled by a rope which runs down through the middle of the envelope to the basket. If the pilot wants to bring the balloon down, he or she simply pulls on the rope which will open the valve, letting hot air escape, decreasing the inner air temperature. This cooling of air causes the balloon to slow its rise.
The pilot can operate horizontally by changing the vertical position of the balloon because the wind blows in different directions at different altitudes. If the pilot wants to move in a particular direction, he or she simply arises and falls to the appropriate level and rides with the wind.
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