(c) 2009 -2014 by Ed Seykota
Radial Momentum is a property of fluid that explains lift
in the levitator and in other devices.
The Bernoulli Principle is a statement of conservation of energy.
Although it is correct, it does not explain lift
in the levitator and other devices.
On this site, I present some cool toys
including a levitator, a paper cone
and some fancy squirt guns.
You can make a levitator
from a spool of thread and a card.
When you blow air down onto the card
the card sticks to the bottom of the spool!
This is a diagram of how the air flows
down the tube and out across the card.
High School and College science books
try to explain how this curious device works
by using Bernoulli's Equation.
They say that Bernoulli's Equation says
that fast-moving air has low pressure.
From that, they say that since the air moves faster
over the top of the card than under the bottom of the card
the pressure above the card is lower
and the greater pressure below pushes the card up.
I claim that Bernoulli's Equation
says nothing of the kind.
If it were true that fast air has lower pressure,
you could take a big old jar of air,
put an altimeter in the jar, screw on the top,
take the jar out for a fast ride in your car,
and see the pressure in the jar drop.
I claim that using Bernoulli's Equation
as an explanation for lift
constitutes out-and-out Bernoulli Abuse.
Stop Bernoulli Abuse
To prove my point, I run some experiments
Collapsing Cone Experiment
Non-Collapsing Tube Experiment
If fast air goes with low pressure,
both tubes would collapse
when you blow air through them.
Actually, only the cone shape collapses,
indicating the pressure drop
has something to do with the air
fanning out into a larger volume.
Levitator Table Setup
To get some precise measurements,
I build a levitator table, complete with instruments
to measure air pressure and air flow.
Cavitation Ring Experiment
I also predict the existence of a cavitation ring
and sure enough, I find one.
The Point of it All
This site presents the case
that levitation has to do with Radial Momentum,
not with fluid velocity.
The High School Physics Hoax
If you look in high school physics books
you may find a couple standard diagrams
Airplane Wing Cross Section
This diagram is part of a goofy theory
that since air flows faster over the top of the wing
and slower under the bottom of the wing.
the pressure on the top is lower
and therefore the wing rises.
You may recall seeing this diagram in high school.
You may also recall a feeling of confusion
about something being not quite right.
Large to Narrow Pipe Diagram
The same people who bring us the wing diagram
also bring us the large-to-narrow pipe diagram
to show how it all works.
They try to use this diagram to try to prove
that high velocity and low pressure go together.
Here's how their song goes:
I Claim this Math Represents Bernoulli Abuse.
First, the math is true only for self-containing systems.
Second, it is true only for constant density.
From #1: the only system for which you can use this math
is a self-containing hollow donut containing air.
From #2: the donut cannot have a fan in it to motivate the air to move.
In such a donut, there is nothing to move the air around the loop
so it comes to rest with zero velocity.
In this case, the math is, actually correct, since 0 = 0.
For cases involving air that actually moves around,
trying to use Bernoulli's Principle
to show that fast air goes with low pressure
is just plain goofy.
By the way,
the assumption about constant density is particularly goofy,
density change is the explanation for the levitator.
Radial Momentum Offers a Better Explanation
The Radial Momentum explanation is that
as the air fans out radially, from the center of the device
it expands into larger and larger volumes
and so it becomes less and less dense.
It is this lower density that explains the lower pressure.
To test this, I design the Tube and Cone Experiment .
The cone collapses and the tube does not collapse.
This indicates that air fanning out goes with pressure drop
and that fast air makes little difference.
The Cone Collapses
The Tube does not Collapse
To further test this out, I make a levitator table
that is basically a big plastic see-through version
of the spool of thread levitator
in which I can measure the air flow and pressure.
Fancy Levitator Table
The flow meter is on the left
and the pressure meter is on the right.
View from Underneath
The air flows through a 1/8" hole in the table.
I try my levitator table with various kinds of cards
Cards are easy to come by here in Nevada.
I find they all stick to the bottom of the table
when I blow air down the hole onto the cards.
Next I try my levitator table with smooth plastic disks.
The disks stick too.
Then I build some special disks - ones with channels.
The point of the channels is to force the air
to flow in different ways.
Detail of Hourglass Channel Disk
I then try these disks with my levitator
to see what happens.
All the disks stick to the levitator
when I put the smooth side up.
When I put the channel sides up,
all except one sticks.
The one that does not stick
is the one with the parallel channel.
This is the only one that does not allow
radial expansion of the air.
So this is further evidence
that Radial Momentum, not air speed
is the explanation for lift.
The Professor and His Business Card
I show my results to a professor from a nearby college.
He specializes in fluid dynamics
and he says he thinks I'm crazy.
He says I am going up against 300 years of science
and that there is no way I'm right.
Furthermore, he shows me a pile of exam papers.
They are the final exams for his graduating college seniors.
The exam question has to do with, of all things, the levitator.
I point out the errors in the exams,
that are the same errors they have from his teaching them.
We are not really off on a good foot.
He tells me he has a way to prove he is right
about high velocity going with low pressure.
He suggests I build a table with a slit in it
rather than a hole in it.
The slit would broadcast air in a linear ribbon
that does not expand radially.
If the card sticks to a slit,
it would prove the velocity theory.
The Business Card Levitator Experiment
I build the experiment according to his suggestion.
The Slit Levitator
The air enters through the fitting at the right
and emerges out the slit that holds the card.
In operation, the card sits on the top plate
flat, between the "headboards."
To make it all the more dramatic,
I use one of the professors own business cards
as the levitation card.
I turn on the pump and run the experiment.
The card does not stick to the equipment.
This is further proof that radial expansion
and not air velocity is the correct explanation
for lift in the levitator.
I call the professor with the good news
that he and all his students have it wrong.
He is not happy with the news.
He does not want to discuss the matter further with me.
I assume he is still busy teaching bad science
to his seniors.
Fun with Water
I run further experiments with water.
The results are much more vivid.
Parallel Channel Water Nozzle
Hourglass Channel Water Nozzle
The Hourglass Works as a Levitator
Again, the parallel channel does not levitate.
The effect with water is stronger
since water is less compressible
so pulling it apart, even a little bit
generates a strong vacuum.
The Ring of Air
The Ring of Air
The basic radial Momentum idea is that the air
expands out radially, by momentum,
into larger and larger rings of air.
If the same mass of air occupies a larger volume
its density is less and the pressure goes down with density.
Note: the Ideal Gas Law states: pV = nRT.
(Pressure x Volume = amount x gas_constant * Temperature).
This law is by Emile Clapeyron, 1834
who combines Boyle's Law and Charle's Law.
Therefore pressure is proportional to density (n/V).
I build a computer model, using Radial Momentum as the organizing principle.
Computer Model Output
The model shows the pressure, velocity, density, mass and mass flux
running from the center of the disk (left) out to the edge (right).
The model shows the pressure drops right around center
in a region I call the active zone.
The pressure reaches a minimum in a ring around the central orifice.
This low pressure motivates the air to increase in velocity,
imparting additional radial momentum to the particles.
As these particles continue radiating outward from the center,
the fluid becomes less dense and the pressure falls.
As the particles flow past the minimum pressure ring,
they experience back-pressure and this tends to slow them further.
The velocity continues to fall until the Radial Momentum dissipates,
the pressure rises to slightly above ambient pressure
and the fluid gently drains at the edge of the disk.
The Cavitation Ring
According to the model, the lift effect occurs
in a small active region around the center of the disk.
I begin searching for evidence of this ring.
I take the equipment outside into the back yard
where I can use water to drive it.
Portable Levitator with Water as the Fluid
The jet from house travels about 30 feet.
If you hold your hand in front of it, it deforms your hand
and feels painful.
Close-Up of the Portable Levitator
The water emerges through a small hole in the center of the disk.
Bringing the Disk up to the Levitator
The stream of water hits the disk and sprays everywhere.
The stream is still pushing the disk away.
Note: experimenters sometimes have to subject themselves
to enormous hardships in the pursuit of scientific knowledge.
When the disk comes flush with the levitator, the levitator "captures" it
The disks stick together with several pounds of force.
Consistent with the Radial Momentum model,
the water gently emerges from around the edge of the disk.
Levitation, another View
The author uses his left hand to keep the disk from sliding to the side.
He is applying little or no upward pressure on the disk.
The stream of water from the hose is levitating the disk.
It Works Under Water
I test the effect under water, at the suggestion of a colleague.
The effect works under water.
Without the levitation effect holding the disk to the levitator,
the water jet from the hose would shoot back out of the dish.
Looking for the Ring
Underside of the Levitator (upper left). The disk (lower right) has a handle on it.
I first run the test at low pressure, by crimping the hose.
I notice a faint white ring around the central hole.
This is a ring of tiny air bubbles,
emerging from the water
as the low pressure sucks them out.
Turning up the Flow
I let the hose go a little bit, increasing the flow.
The cavitation ring becomes bigger and whiter.
Even More Flow
The ring gets bigger and whiter.
I let the hose go, full on.
The ring gets even bigger and whiter.
Water on the Back of a Dish
You can see a very thin layer of water
in the "active region" in the center of the dish
and a "hydraulic jump" a couple inches from the center.
This is similar to the pressure profile of the levitator.
Jet Aircraft with Trailing Ring
My guess is that the nose of the craft (and the cockpit)
divert the air into an expanding ring pattern
so the air expands radially around the nose-to-tail axis.
This results in a decrease of pressure and temperature
in the active region - and the humidity in the air
condenses momentarily to produce a visible cloud.
Flow Versus Pressure for a 3.9 oz. Disk Using Air
I take some measurements on the levitator table
to determine the flow versus pressure chart.
For low head pressure (from the pump)
the flow is about 2.5 standard cubic feet per minute.
As the pressure rises, the flow decreases !
This is due to the levitation effect
bringing the disk closer to the levitator
and restricting the flow.
Levitator lift is a function of Radial Momentum.
Fast or Slow air has nothing to do with it.
The Bernoulli equation is an energy balance equation.
It does not apply to the levitator.
Word of Caution
Stop Bernoulli Abuse.
Daniel Bernoulli (1700-1782)
"It would be better for the true physics
if there were no mathematicians on earth."
-- Daniel Bernoulli
The End (for now).