Why does a spring bubble up from the ground?
What makes the water come up through the pipe into your house?
Why is a fire engine needed to pump water up high?
You remember that up where the pull of the earth and the sun balance
each other, water could not flow or flatten out. Let us try to imagine
that water, here on the earth, has lost its habit of flattening out
whenever possible--that, like clay, it keeps whatever shape it is
given.
First you notice that the water fails to run out of the faucets. (For
in most places in the world as it really is, the water that comes
through faucets is simply flowing down from some high reservoir.)
People all begin to search for water to drink. They rush to the rivers
and begin to dig the water out of them. It looks queer to see a hole
left in the water wherever a person has scooped up a pailful. If
some one slips into the river while getting water, he does not drown,
because the water cannot close in over his head; there is just a deep
hole where he has fallen through, and he breathes the air that comes
down to him at the bottom of the hole. If you try to row on the water,
each stroke of the oars piles up the water, and the boat makes a deep
furrow wherever it goes so that the whole river begins to look like a
rough, plowed field.
When the rivers are used up, people search in vain for springs. (No
springs could flow in our everyday world if water did not seek its own
level; for the waters of the springs come from hills or mountains, and
the higher water, in trying to flatten out, forces the lower water up
through the ground on the hillsides or in the valleys.) So people have
to get their water from underground or go to lakes for it. And these
lakes are strange sights. Storms toss up huge waves, which remain as
ridges and furrows until another storm tears them down and throws up
new ones.
But with no rivers flowing into them, the lakes also are used up in
time. The only fresh water to be had is what is caught from the rain.
Even wells soon become useless; because as soon as you pump up the
water surrounding the pump, no more water flows in around it; and if
you use a bucket to raise the water, the well goes dry as soon as the
supply of water standing in it has been drawn.
You will understand more about water seeking its own level if you do
this experiment:
EXPERIMENT 1. Put one end of a rubber tube over the narrow
neck of a funnel (a glass funnel is best), and put the other
end of the tube over a piece of glass tubing not less than
5 or 6 inches long. Hold up the glass tube and the funnel,
letting the rubber tube sag down between them as in Figure
1. Now fill the funnel three fourths full of water. Raise the
glass tube higher if the water starts to flow out of it. If
no water shows in the glass tube, lower it until it does.
Gradually raise and lower the tube, and notice how high the
water goes in it whenever it is held still.
This same thing would happen with any shape of tube or funnel. You
have another example of it when you fill a teakettle: the water rises
in the spout just as high as it does in the kettle.
[Illustration: FIG. 1. The water in the tube rises to the level of the
water in the funnel.]
WHY WATER FLOWS UP INTO YOUR HOUSE. It is because water seeks its own
level that it comes up through the pipes in your house. Usually the
water for a city is pumped into a reservoir that is as high as the
highest house in the city. When it flows down from the reservoir, it
tends to rise in any pipe through which it flows, to the height at
which the water in the reservoir stands. If a house is higher than the
surface of the water in the reservoir, of course that house will get
no running water.
WHY FIRE ENGINES ARE NEEDED TO FORCE WATER HIGH. In putting out a
fire, the firemen often want to throw the water with a good deal of
force. The tendency of the water to seek its own level does not always
give a high enough or powerful enough stream from the fire hose; so a
fire engine is used to pump the water through the hose, and the stream
flows with much more force than if it were not pumped.
_APPLICATION 2._ A. C. Wheeler of Chicago bought a little farm
in Indiana, and had a windmill put up to supply the place with
water. But at first he was not sure where he should put the
tank into which the windmill was to pump the water and from
which the water should flow into the kitchen, bathroom, and
barn. The barn was on a knoll, so that its floor was almost as
high as the roof of the house. Which would have been the best
place for the tank: high up on the windmill (which stood on
the knoll by the barn), or the basement of the house, or the
attic of the house?
[Illustration: FIG. 2. Where is the best location for the tank?]
_APPLICATION 3._ A man was about to open a garage in San
Francisco. He had a large oil tank and wanted a simple way
of telling at a glance how full it was. One of his workmen
suggested that he attach a long piece of glass tubing to the
side of the tank, connecting it with an extra faucet near the
bottom of the tank. A second workman said, "No, that won't do.
Your tank holds ever so much more than the tube would hold, so
the oil in the tank would force the oil up over the top of the
tube, even when the tank was not full." Who was right?
[Illustration: FIG. 3. When the tank is full, will the oil overflow
the top of the tube?]