A
It is easier to float in the ocean than it is to float in a swimming pool. Do you know why?
Ocean water is full of salt and salt water can hold up more weight than fresh water. See for yourself!
You Will Need:
●3 cups of warm water
●Measuring cup
●Wide-mouthed jar
●Salt
●Spoon
●Raw potato
You Will Do:
1. Pour 1. 5 cups of warm water into the jar.
2. Add 1/3 cup of salt.
3. Stir(搅拌) until the salt is completely dissolved.
4. Add another 1. 5 cups of water. Pour it slowly over the back of the spoon into the jar so that the two liquids will not mix together.
5. Gently place the potato into the jar. Do not drop it.
What Will Happen:
The potato will sink— but only halfway!
Why?
Salt water is heavier than fresh water, so it will stay on the bottom. The fresh water will remain on top.
The potato is heavier than the fresh water, but it is lighter than the salt water. That is why the potato will sink halfway down.
【文章大意】在海洋中漂浮比在泳池更容易, 因为海洋中富含盐分, 盐水比淡水承载更多的重量。
21. In which step of the experiment do you add the salt?
A. Step 1. B. Step 2. C. Step 3. D. Step 4.
【解析】选B。细节理解题。根据文中You Will Do: . . . 2. Add 1/3 cup of salt. 可知在第二步中你需要加入盐, 故选B。
22. In Step 4 of the experiment, why do you pour the water over the spoon “slowly”?
A. Because it is easier to see what you are doing.
B. Because it pushes the fresh water to the bottom.
C. Because it will keep the water from coming out.
D. Because it will keep the liquids from mixing together.
【解析】选D。推理判断题。根据实验第四步Pour it slowly over the back of the spoon into the jar so that the two liquids will not mix together. 可知, 缓慢加入水, 是为了不让两种液体混合在一起。
23. In the experiment, what should you do right after you pour the water over the spoon?
A. Add the salt to the water.
B. Stir the salt into the water.
C. Place the potato in the jar.
D. Pour warm water into the jar.
【解析】选C。细节理解题。根据实验第五步 5. Gently place the potato into the jar. Do not drop it. 可知注入水以后要轻轻地把土豆放入广口瓶, 故选C。
