雅思考试口语话题 科学课

　　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.