Man's physical universe



Fig. 160. The path of a baseball is

curved by the spin given the ball by

the pitcher.

tion of the balls piles up air on one

side and reduces the pressure on

the other side, as shown in Fig. 161.

The path of the ball is therefore

deflected toward the direction of

least pressure.

A ping-pong ball will be supported

in an air stream or a jet

of water, as shown in Fig. 162,

and is prevented from falling off

the jet.

Figure 163 shows how a card

with a pin projecting up into the hole in a spool is held near the

spool when air is blown through the spool, because the velocity of

. Direction of

Spinning Bail

Direction of Air

Relative to Ball

Fig. 161. Bernoulli's

principle applied to a

"curved" baseball.

Increased Pressure

(Decreased Velocity)

Decreased Pressure

(Increased Velocity)

the air is increased and therefore the pressure is decreased above the

card to a value lower than the atmospheric pressure below it.

The same principle is applied in the automobile

carburetor, where a stream of air flows through a

narrow passage and thus sucks in gasoline from the

jets and mi.xes with it.

The steam-injector, used in forcing water into

boilers at high pressures, is based on this same principle.

Two ships at anchor near each other in a river

current or tide or two ships moving through the water

side by side may be drawn together in the same

way that the tennis balls hung near each other by

long threads will be drawn together when a jet of

air is blown between them.

The Lift

Opposes the Force of Gravity.

The force which lifts the airplane from the earth

and sustains it while in flight is called the lift.

High Velocity

Low Pressure


Fig. 162.

A ball

supported on a

blast of air. — An

illustration of Bernoulli's


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