Wordly Wise Lesson 9

The air inside a hot-air balloon is heated. This makes it less ______ than the surrounding cooler air and causes the balloon to rise.

In 1783 a large crowd assembled to watch the Montgolfier brothers' hot-air balloon. Among the ______ were members of the French royal family.

The Montgolfier brothers' hot-air balloon reached a height of 1,500 feet. Its flight _______ after it had been in the air for eight minutes.

Unlike a kite, the Montgolfier brothers' hot air balloon was not attached to the ground. People watched in amazement as the balloon ________ to a great height.

A sheep, a duck, and a rooster were the first airborne creatures. Two months later, the first human flight in a balloon took place, a truly _________ act.

By 1900, there was great competition to build a successful heavier-than-air machine. The first to _______ this goal would be famous.

The Wright brothers made and repaired bicycles for a living. They ________ their work on bicycles to concentrate on building a heavier-than-air machine.

Some early aircraft had as many as six wings, stacked above each other. Such airplanes were too _______ to ever get off the ground.

Modern aircraft have rigid wings. Early attempts to ________ the flapping of birds' wings ended in failure.

The first aircraft designers had a problem in trying to reduce the plane's weight. The lighter the aircraft, the more _______ it was.