ight?

_APPLICATION 18._ James McDougal lived in a hilly place. He
was going to buy a bicycle. "I want one that will take the
hills easily," he said. The dealer showed him two bicycles.
On one the back wheel went around three times while the pedals
went around once; on the other the back wheel went around
four and a half times while the pedals went around once. Which
bicycle should James have chosen? If he had wanted the bicycle
for racing, which should he have chosen?

_APPLICATION 19._ A wagon stuck in the mud. The driver got out
and tried to help the horse by grasping the spokes and turning
the wheel. Should he have grasped the spokes near the hub,
near the rim, or in the middle?

[Illustration: FIG. 33. With this arrangement the pail travels more
slowly than the hand. Will it seem heavier or lighter than with the
arrangement shown in Figure 32?]

INFERENCE EXERCISE

Explain the following:

71. When you turn on the faucet of a distilled-water bottle,
bubbles go up through the water as the water pours out.

72. A clothes wringer has a long handle. It wrings the clothes
drier than you can wring them by hand.

73. You use a crowbar when you want to raise a heavy object
such as a rock.

74. Sometimes it is almost impossible to get the top from a
jar of canned fruit unless you let a little air under the edge
of the lid.

75. It is much easier to carry a carpet sweeper if you take
hold near the sweeper part than it is if you take hold at the
end of the handle.

76. You can make marks on a paper by rubbing a pencil across
it.

77. A motorman sands the track when he wishes to stop the car
on a hill.

78. On a faucet there is a handle with which to turn it.

79. Before we pull candy we butter our fingers.

80. You can scratch glass with very hard steel but not with
wood.

SECTION 11. _Inertia._

Why is it that if you push a miniature auto rapidly, it will
go straight?

Why does the earth never stop moving?

When you jerk a piece of paper from under an inkwell, why does
the inkwell stay still?

When you are riding in a car and the car stops suddenly, you are
thrown forward; your body tends to keep moving in the direction in
which the car was going. When a car starts suddenly, you are thrown
backward; your body tends to stay where it was before