Bernoulli’s Principle
To understand Bernoulli’s
Principle, think about what
happens when a a fluid such as
air or water moves.
Think about what happens if you
hold a plastic spoon in a stream
of running water.
You might predict that the spoon
would be pushed away by the
water. But it is not. Surprisingly,
the spoon is pushed toward the
stream of water. The behavior of
Daniel Bernoulli
 The Swiss scientist Daniel Bernoulli found that the
faster a fluid moves, the less pressure the fluid
exerts.
 Bernoulli’s principle states that the pressure exerted
by a moving stream of fluid is less than the pressure
of the surrounding fluid.
 The water running along the spoon is moving but
the air on the other side of the spoon is not.
The moving water exerts less pressure than the still
air.
 The result is that the greater pressure of the still air
on one side of the spoon pushes the spoon into the
stream of water.
Another Example
If you blow above a sheet of
tissue paper, the paper rise.
Moving air blown over the tissue
paper , the paper will rise.
Moving air blown over the tissue
paper exerts less pressure than
the still air blown the paper.
The greater pressure below the
paper pushes it upward.
Objects in Flight
Bernoulli’s principle is one factor
that can help explain flight - from
a small bird to a huge airplane.
Objects can be designed so that
their shapes cause air to move at
different speeds above and
below them.
If air moves faster above the
object, pressure pushes the
object upward.
But if air moves faster below the
object, pressure pushes it
Bernoulli’s Principle at
Home
Bernoulli’s principle can help you
understand many common occurrences.
For example, you can sit next to a
fireplace enjoying a cozy fire thanks in part
to Bernoulli’s principle.
Smoke rises up the chimney partly
because hot air rises, and partly because it
is pushed.
Wind blowing across the top of the
chimney lowers the air pressure there.
The higher pressure at the bottom then
Take a look…
Turn to page 99 and lets
read Exploring Wings and
how Bernoulli’s principle
helps explain how air moving
around a wing produces a
force.
Figure 20
Turn to page 100 and lets
read how Bernoulli’s principle
helps us understand how an
atomizer works.