题型:阅读理解 题类:常考题 难易度:普通
人教版(新课程标准)高中英语必修5 Unit 5同步练习三
"Depend on yourself" is what nature says to everyone. Parents can help you. Teachers can help you. Others can help you. But all these only help you to help yourself.
There have been many great men in history. But many of them were poor in childhood, and had no uncles, aunts or friends to help them. Schools were few and not very good. They could not depend on them for education. They saw how it was, and set to work with all their strength to know something. They worked their own way till they became wellknown.
One of the most famous teachers in England used to tell his pupils, "I can not make worthy men of you, but I can help you make men of yourselves."
Some young men do not try their best to make themselves valuable to the human beings. They can never gain achievements unless they see their weakpoints and change their courses. They are nothing now, and will be nothing as long as they live, unless they accept the advice of their parents and teachers, and depend on their own honest efforts.
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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