hem to buoy them up.
Cork would be all right, but it isn't as light as air; so air
would be the best thing to fill them with."

Which way would the floats have worked best?

_APPLICATION 7._ A little girl was telling her class about
icebergs. "They are very dangerous," she said, "and ships are
often wrecked by running into them. You see, the sun melts
the top off them so that all there is left is under water. The
sailors can't see the ice under water, and so their ships
run into it and are sunk." Another girl objected to this; she
said, "That couldn't be; the ice would bob up as fast as the
top melted." "No, it wouldn't," said a boy. "If that lower
part wasn't heavier than water, it never would have stayed
under at all. And if it was heavier at the beginning, it would
still be heavier after the top melted off."

Who was right?

INFERENCE EXERCISE

Explain the following:

11. When you wash dishes, a cup often floats on top of the
water, while a plate made of the same sort of china sinks to
the bottom of the pan.

12. If you put the cup in sidewise, it sinks.

13. The water in the cup, when lying on its side, is exactly
as high as the water in the dish pan.

14. If you put a glass into the water, mouth first, the water
cannot get up into the glass; if you tip it a little, there
are bubbles in the water and some water enters the glass.

15. If you let a dish slip while you are wiping it, it crashes
to the floor.

16. It is much harder to hold a large platter while you are
wiping it than it is to hold a small butter plate.

17. If you set a hot glass upside down on the oilcloth table
cover, the oilcloth bulges up into it when the hot air and
steam shrink and leave a partial vacuum within the glass.

18. If you spill any of the dishwater on the floor, it
flattens out.

19. You may use a kind of soap that is full of invisible
little air bubbles; if you do, the soap will float on top of
the water.

20. When you drop a dry dishcloth into water, it floats until
all the pores are filled with water; then it sinks.

SECTION 5. _How things are kept from toppling over: Stability._

Why is it harder to keep your balance on stilts than on your
feet?

Why does a rowboat tip over more easily if you stand up in it?

In Pisa, Italy, there is a