e is not flat but rounded.

56. It is hard to write on cloth because the ink spreads out
and blurs.

57. If you roughen your finger nails by cleaning them with a
knife, they will get soiled much more quickly than if you keep
them smooth by using an orange stick.

58. When you dip your pen in the ink and then move it across
the paper, it makes ink marks on the paper.

59. If you suck the air out of a bottle, the bottle will stick
to your tongue.

60. You cannot break a thick piece of iron with your hands.

SECTION 9. _Friction._

What makes ice slippery?

How does a brake stop a car?

Why do things wear out?

It would not be such a calamity if we were to turn off friction from
the world. Still, I doubt whether we should want to leave it off much
longer than was necessary for us to see what would happen. Suppose we
imagine the world with all friction removed:

A man on a bicycle can coast forever along level ground. Ships at
sea can shut off steam and coast clear across the ocean. No machinery
needs oiling. The clothes on your body feel smoother and softer than
the finest silk. Perpetual motion is an established fact instead of an
absolute impossibility; everything that is not going against gravity
will keep right on moving forever or until it bumps into something
else.

_But_, if there is no friction and you want to stop, you cannot.
Suppose you are in an automobile when all friction stops. You speed
along helplessly in the direction you are going. You cannot steer the
machine--your hands would slip right around on the steering wheel, and
even if you turn it by grasping the spoke, your machine still skids
straight forward. If you start to go up a hill, you slow down, stop,
and then before you can get out of the machine you start backward
down the hill again and keep on going backward until you smash into
something.

A person on foot does not fare much better. If he is walking at the
time friction ceases, the ground is suddenly so slippery that he falls
down and slides along on his back or stomach in the same direction he
was walking, until he bumps into something big or starts to slip up
a slope. If he reaches a slope, he, like the automobile, stops an
instant a little way up, then starts sliding helplessly backward.

Another man is standing still when the friction is turned off. He
cannot get anywhere. As soon as he starts to walk forward, his feet