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
·Glass rod
·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 down the glass rod 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 the 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.
21.In which step of the experiment do you add the salt?
A.Step 1. B. Step 2. C.Step 3. D.Step 4.
22.In Step 4 of the experiment, why do you pour the water down the glass rod “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.
23.In the experiment, what should you do right after you pour the water down the glass rod?
A.Add the salt to the water.
B.Stir the salt into the water.
C.Gently place the potato into the jar.
D.Pour warm water into the jar.
