modals

Slide 1

• Modal Verbs B2 (application/pdf)

Slide 2

• THE ROCKET - FROM EAST TO WEST
• A The concept of the rocket, or rather the mechanism behind the idea of propelling an
• object into the air, has been around for well over two thousand years. However, it wasn’t until the discovery of the reaction principle, which was the key to space travel and so represents one of the great milestones in the history of scientific thought, that
• rocket technology was able to develop. Not only did it solve a problem that had intrigued man for ages, but, more importantly, it literally opened the door to exploration of the universe.
• B An intellectual breakthrough, brilliant though it may be, does not automatically ensure that the transition is made from theory to practice. Despite the fact that rockets had been used sporadically for several hundred years, they remained a
• relatively minor artefact of civilisation until the twentieth century. Prodigious efforts, accelerated during two world wars, were required before the technology of primitive rocketry could be translated into the reality of sophisticated astronauts. It is strange that the rocket was generally ignored by writers of fiction to transport their heroes to mysterious realms beyond the Earth, even though it had been commonly used in
• fireworks displays in China since the thirteenth century. The reason is that nobody associated the reaction principle with the idea of travelling through space to a neighbouring world.
• C A simple analogy can help us to understand how a rocket operates. It is much like a machine gun mounted on the rear of a boat. In reaction to the backward discharge of bullets, the gun, and hence the boat, move forwards. A rocket motor’s ‘bullets’ are minute, high-speed particles produced by burning propellants in a suitable chamber.
• The reaction to the ejection of these small particles causes the rocket to move forwards. There is evidence that the reaction principle was applied practically well before the rocket was invented. In his Noctes Atticae or Greek Nights, Aulus Gellius
• describes ‘the pigeon of Archytas’, an invention dating back to about 360 BC.
• Cylindrical in shape, made of wood, and hanging from string, it was moved to and fro by steam blowing out from small exhaust ports at either end. The reaction to the discharging steam provided the bird with motive power.
• reading

Slide 3