教材文本 Unit 2 Comprehending

Unit 2 Sailing the OceansComprehending1 Read the passage and answer the following questions. 1 What is the use of a beating circle, astrolabe, quadrant or sextant? ( ) What is the use of a compass? ( ) A to set the course of the ship B to measure the position of the ship C to measure the speed of the ship D to tell the time2 Why are speed and time important in working out the longitude of a ship?3 Why is the position of the sun and various stars useful for working out latitude?2 Suppose you were a sea captain aiming to sail round Africa. Discuss in groups: 1 What skills would you seek in your sailors?2 What problems would you anticipate for this journey?3 What would you do if you came across the following problems during your voyage? Read the char below and fill in your plans of action to deal with them. What would you do if:Plan of actionYou were far from land and a storm arose. You knew your latitude but didnt know your longitude. You were blown off-course. You were offshore but you needed more food and water. You wanted to keep a straight course. You were lost with no land in sight. 4 Read the passage again and use the information to analyse the navigational skills. Write the answers in your own words. Using nature1 To find the ships position at sea a sailor used the North Star and the sun. 2 A sailor knew that land was nearby if he saw _3 Sailors used _ to increase their speed. Using instruments4 There were two methods to find longitude: 1 _ 2 _5 Write down the working principles of the following instruments: Bearing circle: _ Astrolabe: _ Quadrant: _ Sextant: _5 Imagine you are on a boat with twenty-nine other people. You have a small box for your personal things but it can only hold ten items. What would you need for a weeks journey across the North Sea to England?CategoryItemsCategoryItemsClothesShoesHygieneToolsBeddingMedicinesDiscuss your list with your partner and combine the two sets of choices to make a third and better list. Be prepared to justify your choices to the class. Answer key for Exercise 1: 1 B A2 Speed and time are important in finding out the longitude of a ship because the earth moves fifteen degrees westwards every hour. If you know your direction, speed and time, you can work out the approximate longitude or change in your position in relation to the stars. 3 The position of the sun and stars are useful for working out latitude because they are fixed points in the sky and their movements in relation to the earth are already known. So they can be used to measure a ships position. Suggested answers to Exercise 2: 1 The sailors would need to be excellent navigators, able to cope with both hot and cold weather, experienced in sailing through very bad weather and able to co-operate in a team. 2 I would anticipate very hot weather （around the equator）, cold weather（around the Cape of Good Hope）, very stormy seas（around the Cape）, and problems with food and water（unless helped by local natives the water may be contaminated and the food scarce）, etc. Answer key for Exercise 3: What would you do if: Plan of actionYou were far from land and a storm arose.wait till the storm is over and then find your new position and return to your original courseYou knew your latitude but didnt know your longitude.Use knots to find your speed and work out your approximate longitudeYou were blown off-courseuse the compass and the astrolabe, quadrant or sextant to find out your position. return to your former courseYou were offshore but you needed more food and water.Follow nesting birds to shore;Look for special cloud formations or fog over streams to find landYou wanted to keep a straight course.use a compassYou were lost with no land in sight.Measure your position using the sun or stars; look for sea birds, cloud formations, fog or seaweed to show that land is nearbyAnswer key for Exercise 4: 2 fresh seaweed, nesting birds returning home in the evening or fog3 sea currents or tides and winds4 1 measuring time and speed 2 compass and complicated mathematical tables5 Bearing circle: to compare the height of the sun now with the position of the sun at midday. Astrolabe: to compare the position of the ship in relation to some stars or the sun. Quadrant: a more precise form of the astrolabe, to measure how high stars are above the horizon, and compare that measurement with previous measurements（using the ship as one of the fixed points to find its position）. Sextant: an updated version of the quadrant and so it was more accurate, to measure the angle between two fixed points outside the ship（using two mirrors to find the ships position）. Suggested answers to Exercise 5: Note: Do not include food an