雅思考试口语话题 科学课

　　考生普遍认为这个话题卡是09年5月出现的新题当中，最难的一个。我个人认为它确实有些难度，但并不是可怕到无话可说的地步。科学分为很多种，生物，植物，物理，化学…… 大家从其中某一门学科中挑选一个比较生活化，比较通俗易懂的用英文描述出来就可以了，并不需要说那些深奥的科学问题如：外太空黑洞，磁铁的两极，无机化学命名等等。
　　下面挑选一个科学实验的例子，提供一些素材给大家，其实还有很多可以选择，时间关系，先去上课，晚上回来再给大家补充关于生物和植物方面的口语素材。
　　Describe a science lesson that you had in school or university.
　　You should say:
　　* when you attended this lesson
　　* where you attended this lesson
　　* how you learned it
　　and explain what you learned.
　　Boiling Frog 温水煮青蛙
　　how you learned it
　　* The boiling frog story states that a frog can be boiled alive if the water is heated slowly enough — it is said that if a frog is placed in boiling water, it will jump out, but if it is placed in cold water that is slowly heated, it will never jump out.
　　* If you put the frog in cold water and slowly increase the temperature--slowly boil the water, the frog will be cooked without trying to jump out.
　　* They say that if you put a frog into a pot of boiling water, it will leap out right away to escape the danger. But, if you put a frog in a kettle that is filled with water that is cool and pleasant, and then you gradually heat the kettleuntil it starts boiling, the frog will not become aware of the threat until it is too late. The frog's survival instincts are geared towards detecting sudden changes.
　　explain what you learned
　　* The story is often used as a metaphor for the inability of people to react to important changes that occur gradually.
　　* Life happens gradually. Like the frog, we can be fooled, and suddenly it’s too late. We need to be aware of what is happening.
　　* This is a story that is used to illustratehow people might get themselves into terrible trouble. This parable is often used to illustrate how humans have to be careful to watch slowly changing trends in the environment, not just the sudden changes. Its a warning to keep us paying attention not just to obvious threats but to more slowly developing ones.
　　* An example: Let's say that every year, the local well had an inch less of water in it. A person might realize there's a problem if there's suddenly NO water, but a slowly dropping level might not be an obvious crisis until it's too late!
　　其他素材：
　　Domino Effect 多米诺效应
　　how you learned it
　　* Setting up a chain of dominoes stood on end, and toppling the first domino. That domino topples the one next to it, and so on. In the experiment, however long the chain the dominoes will still fall.
　　explain what you learned
　　* This is because the energy required to topple each domino is less than the energy transferred by each impact, so the chain is self-sustaining. Energy is stored by setting each domino in the metastable upright position, and that energy is what keeps the chain toppling.
　　* The domino effect is a chain reaction that occurs when a small change causes a similar change nearby, which then will cause another similar change, and so on in linearsequence.
　　Coins Turned Green 硬币氧化变绿
　　Materials you will need:
　　Saucer
　　Vinegar
　　A Penny
　　Kitchen/Paper Towel
　　Steps:
　　1. Fold the kitchen/paper towel a few times to get a bit of thickness.
　　2. Lay the kitchen/paper towel on top of the saucer and pour out some vinegar until it is soaked up by the kitchen/paper towel.
　　3. Place the penny on the kitchen/paper towel and leave it there.
　　4. Keep a check on the penny and observe the chemical reaction.
　　5. Leave it for a full day to get the best results.
　　This is very exciting to observe! What happened to the penny? It turned green.
　　Coloured Flower 变色的花
　　Materials you will need:
　　Water
　　Scissors
　　Food Colouring
　　Jar, Plastic Cup or Test Tube
　　A Flower (light coloured-white carnation) or Celery Stalk (with leaves)
　　This is a colour changing experiment.
　　Steps:
　　1. Fill the cup with water.
　　2. Add a few drops of food colouring
　　3. Cut the end off the stem (stalk)
　　4. Put the flower in the water
　　Watch and in time the food colouring will be sucked up the stem along tiny tubes (called vessels) and the petals of the flower will start to change in colour.
　　Another way to try this experiment is to get a flower with a long, thick stem (or a celery stalk with leaves) and slit it carefully from the bottom and put one end in separate test tubes (with different food colourings). Your flower (or celery) should have petals (or leaves) in two different colours.
　　Did you know that plants need water to live? As well as absorbing water from the atmosphere (air) through their leaves, they suck water up through their stems. If you used the celery stalk for the above experiment you could cut the stalk and see that the little holes inside are coloured.