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 (量杯)
● Wide-mouthed jar
● Salt
● Spoon
● Raw (生的)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.
1. 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 thejar.
2. In Step 4 of the experiment, why do you pour the water over the spoon “slowly”?
A. It is easier to see what you are doing.
B. It pushes the fresh water to the bottom.
C. It will keep the water from coming out.
D. It will keep the liquids from mixing together.
3. In which step of the experiment do you add the salt?
A. Step 1 B. Step 2
C. Step 3 D. Step 4
【答案】1. C 2. D 3. B
【解析】
本文介绍了一个证明盐水的浮力比淡水的浮力大的实验。
【1题详解】
C
细节理解题。根据You Will Do:中的5 Gently place the potato into the jar. Do not drop it.可知，在实验中，当你把水倒在勺子上后，你应该把土豆放入坛子中。故选C.
【2题详解】
D
细节理解题。根据Add another 1.5 cups of water. Pour it slowly over the back of the spoon into the jar so that the two liquid will not mix together中的so that the two liquid will not mix together指这两种液体不要混在一起。故选D.
【3题详解】
B
细节理解题。根据You Will Do:中的2 Add 1/3 cup of salt.可知，要在第2步时加盐。故选B。
