Transcript Exploring Bernoulli’s Principle

Pneumatic and Electro-Mechanical Circuits
Exploring Bernoulli’s Principle – Level 2
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What You’ll Learn…
 Facts about Bernoulli’s Principle and how it relates to air speed
and pressure
 Three fun ways to visually demonstrate Bernoulli’s Principle
using ping-pong balls and golf balls
 What the Venturi effect is and how it has been applied in several
commonly used inventions
 Safety tips when working with your pneumatics kit
Stuff You’ll Need…
 Pneumatics Lab Kit
 3 Ping-pong balls and a golf ball
 Digital camera
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What You Should Know…
Discovering the laws of fluid dynamics…
Today you are going to discover some really fun experiments you can do
demonstrate the scientific principles involved with fluid dynamics, which is
the science of fluids in motion.
In 1738, a Dutch mathematician named Daniel Bernoulli published what
has become known as Bernoulli's Principle. Bernoulli Principle simply
stated, says that the pressure of a fluid decreases when the speed of the
fluid increases. Both liquids and gases are fluids, so this principle applies to
rivers and streams as well as to the flow of air.
About 40 years later an Italian physicist named Giovanni Battista Venturi
discovered that fluids increase their speed as they flow through a narrow
constricted section of a pipe. And sure enough, the pressure decreases in
the constricted section just like Bernoulli said it would. Venturi’s discovery,
known as the Venturi effect, lead to the invention of many different practical
devices that apply this simple principle. The Venturi carbeurator, Venturi
vacuum pumps, and all kinds of sprayers are expamples of tools that use
the Venturi effect.
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What You Should Know…
The Venturi effect is applied to the engineering of products…
Venturi’s discovery, known as the Venturi
effect, lead to the invention of many different
practical devices that apply this simple
principle. When gases like air, or liquids pass
through a narrow spot in a pipe it creates a
lower pressure in that area because the flow
rate speeds up inside the narrow section.
Many products like paint sprayers and
garden fertilizer sprayers utilize this
technology. The test section of the Jet
Stream 500 wind tunnel also forms a Venturi
shape, so the low pressure in the test section
helps secure the side door because of the
vacuum (low pressure) inside.
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What You Should Know…
The Venturi effect is applied to the engineering of products…
This diagram gives you a visual
representation of the pressure difference
between the large diameter section of the
pipe and the narrow Venturi section.
A
B
You must imagine that the purple color is a
liquid like water. If the pressure in both
sections of the pipe were equal, the water in
both stand pipes A and B would be exactly
the same height.
But you can see that the water level in stand
pipe B is lower. It’s lower because the
pressure inside the narrow section is lower.
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What You Should Know…
The Venturi effect is applied to the engineering of products…
The Venturi effect is being used in this example
of a Venturi vacuum sprayer.
2
Compressed air represented in blue is injected
into a narrow orfice that creates a high speed,
low pressure condition.
A canister containing a whatever you want to
spray is connected below the sprayer head,
and the liquid inside represented in red is
pulled by the vacuum into the sprayer head. It
then exhausts out the nozzle of the sprayer.
3
1
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What You Should Know…
Fluid dynamics: The study of fluids in motion…
The video you are about to watch will give you valuable background
information and insigths into the science of fluid dynamics as it discusses
concepts related to Bernoulli’s Principle and the Venturi effect.
This tutorial video will also introduce you to the experiments you will be
performing during this Learning Launcher, so watch carefully so that you will
know how to set up and perform each of the different experiments.
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Caution!
Pneumatic Safety first…
It’s always a good idea to develop safe work habits when working with
equipment like your pneumatics workstation. Following the safety rules
outlined below will help prevent accidents and personal injury.
 Safety glass must be worn when ever the air supply is on.
 ALWAYS turn the air supply OFF when connecting or disconnecting tubing
 NEVER use more than 20 psi from your Air Supply.
20 psi
 NEVER point a blowing air tube at yourself or anyone else
 ALWAYS connect your tubing to your circuit components first, then connect to
the Air Supply last. Loose air tubes will whip violently around as air is
escaping out the end if they are not connected to a pneumatic device.
 ALWAYS keep your hair, hands, and fingers away from moving piston rods
that can pinch, punch and severely hurt you.
 NEVER walk away from a live operating circuit you have built leaving it
unattended. Supervising your pneumatic circuits helps prevent accidents.
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Caution!
Proper operation of the bench-top Air Supply…
NOTE: The air pressure
regulator valve is 2-piece.
The outside of the knob
can be pushed down to
lock it, but must be pulled
up before you can turn it
OFF or ON.
Pull UP to
unlock
It’s best if you NEVER
lock the knob. NEVER
use wrenches or channellocks to turn the knob.
When you turn the
air OFF… do not
tighten the knob in
the OFF position.
STOP turning when
the pressure gage
says zero
Never use
tools to turn
this knob
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Do It!
Ping-Pong Ball verses Gravity…
Your first experiment with Bernoulli’s Principle is a challenge to
see if you can balance a ping-pong ball on the top end of a
pneumatic air tube with air blowing out the end. Can you do it?
Regulate the air flow with the air supply regulator. If you are
successful with this challenge, explain why it is possible and how
this relates to Bernoulli’s Principle.
NEVER let go of the
air tube while air is
blowing out the end.
If you do, the tube
will being whipping
around in a very
dangerous manner.
Air Supply Regulator
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Do It!
Ping-Pong Ball verses Gravity…
This is a fun experiment, but can you
explain what is happening?
The blast of fast moving air from your
air tube is creating a low pressure
column that your ping-pong ball gets
trapped in. The surrounding air
molecules are holding the ball in place.
Air Supply
The little blue bubbles
represent the invisible
air molecules that
surround us.
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Do It!
Ping-Pong Ball verses Gravity…
With enough air pressure you can even
hold the floating ping-pong ball pretty
close to horizontal before it falls.
Do you think this experiment would
work with other geometric shapes like
squares for example?
Air Supply
The little blue bubbles represent the invisible
air molecules that surround us. The stagnant
air molecules outside the blast zone are denser
or closer together than the molecules in the
stream of air coming from your air tube.
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Do It!
Ping-pong ball canon challenge…
Now that you’ve had some experience
using the bare end of an air tube to
balance a ping-pong ball, try using a PVC
cap on the end of the tube to turn it into a
ping-pong ball canon. How far do you think
you can blast the canon (ping-pong) ball?
Ping-Pong
Ball Canon
What difference does the size of the PVC
cap make? If you have two different sizes,
try them both and see how the ball
responds to each different size.
You can also use a
plastic bottle cap for
this experiment.
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Do It!
Ping-pong ball canon becomes a vacuum…
Well the canon idea didn’t work very well,
did it. Why do think the PVC cap holds on
to the ball like a vacuum cleaner?
Try holding it straight upside down to see if
the ball drops out. Can you explain why the
cap with air blowing out can act like a
vacuum?
Ping-Pong
Ball Vacuum
Can you pick up a flat
sheet of paper with your
new vacuum machine?
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Do It!
Ping-pong ball pendulum Challenge…
So far each of your experiments seems to
defy common sense. The invisible forces
exerted by air pressure are tricky to
comprehend and understand, aren’t they?
Let’s try a new experiment. You saw it in
the tutorial video, but this time you are
going to do it for yourself.
You need two ping-pong balls hanging from
a string. You can carefully glue the end of a
string with Super glue, hot-melt glue, epoxy,
or whatever you have.
Your goal is to find out which way the
ping-pong balls move when you blow
a jet of air between them.
You need to find a place to
suspend the ping-pong balls.
The edge of your workstation
bench top will work, with a heavy
book to hold the strings.
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Do It!
Ping-pong ball pendulum Challenge…
So which way did they move?
Explain the results of your
experiment with the help of
Bernoulli’s Principle?
Make sure you are
capturing your test with
still shots to be
included in your Word
document.
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Do It!
Spinning a ping-pong ball in the palm of your hand…
You watched this experiment in the
tutorial video also. So now it’s your
turn to do it yourself.
The challenge is to aim the air tube
near the bottom of the ball in order to
make it spin in the palm of your hand.
If you do it just right, the ball will spin
faster and faster until it appears to hit
its maximum speed.
If the ball gets away from you while it is
spinning, it really takes off because of
the spinning motion.
See if you can do it…
and make sure you
capture it.
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Do It!
Spinning a ping-pong ball in the palm of your hand…
Now try the same experiment with a golf
ball like you saw in the tutorial video. This
experiment makes a really cool sound as
the speed of the ball increases.
If you ever have a dentist drill on your teeth
with a pneumatic drill, you may recognize
the similarity of the sound.
Why doesn’t your hand get
burned from friction heat
while the ball is spinning?
Do you think it is possible to
make an air powered motor?
Dentist Drill
Air Motor
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Do It!
Reflecting on what you have learned…
You have completed five different experiments
designed to demonstrate with Bernoulli’s
Principle in action. What have you learned from
your observations?
Would you have expected the results you got if
you hadn’t seen the tutorial video first? Are you
prepared to explain Bernoulli’s Principle to
people who don’t know what it’s about?
Congratulations on your
accomplishments.
Summarize what you learned in
your Word document.
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Do It!
The Bernoulli Family Tree Challenge…
The Bernoulli family is world
famous for their mathematical skills
and numerous contributions to the
world of science.
Daniel Bernoulli
Go online and find out how many
famous members of the Bernoulli
family there are and what they did
to become famous.
Discover for yourself how much
impact the Bernoulli’s had on the
things you study in math and
science classes today.
Who knows, maybe you will
become famous for a
worthwhile contribution you
will some day make to the
world we live in.
The Bernoulli Family Tree
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