(gentle music)
- I've always found these things a little confusing,
glass syringes.
But I discovered something about glass syringes recently
that completely blew my mind.
There's quite a bit of friction between the plunger
and the barrel.
And it needs to be, because it's air tight,
and you can actually hear it,
like if I put it up against the microphone here.
(syringe whirring)
But watch what happens if I give it a spin.
Just keeps going and going.
Isn't that crazy?
All the friction disappears.
Here's a much larger one that I bought
and it does the same thing.
Don't be disheartened by the way,
if you try this with a glass syringe that you have
lying around and it doesn't work to begin with,
sometimes they need a bit of breaking in.
So, give it a spin for a good few minutes first.
Here's another cool thing that it does, watch this.
Boi-oi-oing.
Boi-oi-oing
Boi-oi-oing,
it's a word.
For our completeness, here's a teeny, tiny one.
Even works sideways.
So what's going on here?
Well, to answer that question,
let's look at what makes a glass syringe so remarkable
in the first place.
Compare it to a plastic syringe.
With a plastic syringe, the rubber plunger tip
is manufactured to have a wider diameter
than the internal diameter of the barrel.
So when you push it in, you're squeezing that rubber tip
and it creates a really nice seal making it airtight.
And that's possible because, rubber is elastic.
But glass is hardly elastic at all,
in fact, it's a really rigid substance.
So, the manufacturing tolerance
on these things must be insane.
Like, if you make the plunger just slightly too wide
it won't fit, if you make it slightly too narrow,
it won't be airtight.
And despite those manufacturing demands,
I bought this for about 15 pounds.
And look, it's really airtight,
but also moves really smoothly.
Isn't that amazing?
So for a glass syringe to work,
the plunger needs to be very slightly smaller
than the barrel only by a few microns.
So I suppose, technically, they're not perfectly airtight,
it's just that the gap is so incredibly small
that only a minuscule amount of air could ever escape.
Another criteria is that the cross section of both surfaces
need to be almost perfectly circular.
If you have those conditions,
then when you give the barrel a spin,
something amazing happens,
it turns into a hydrodynamic bearing.
When a hydrodynamic bearing is rotating,
there's actually no contact between the two surfaces
and we could prove that if these parts were made of metal.
Because we could create a circuit
that passes through the syringe
and then show when the bowel is rotating,
that the circuit breaks,
because the surfaces aren't touching.
So I started to ask around to find out,
does anyone have the machining ability
to create something like this in metal
with the kind of tolerance that you need?
Someone called Patrick Herd got in touch and said,
"Actually you can buy components like this off-the-shelf
from the Injection Molding Industry.
He even sent a little video of some of the parts
that he has acting as a hydrodynamic air bearing.
I wish I had an air compressor.
I think I'm gonna buy an air compressor.
I don't know if you've ever tried to buy parts
from Injection Molding on the internet,
it's really confusing.
But fortunately, I came across, eventually,
someone called, Tom Lipton who has a channel called Oxtools.
Tom has this huge workshop and he makes videos
showing you how to use tools, how to make tools.
It's remarkable.
I asked if he'd be interested in collaborating on this,
and he said, "Well, instead of making that thing,
how about we make this thing, that's even more interesting?
It's called a Kingsbury Aerodynamic Bearing."
He made it and he sent it to me in the post.
I'll leave a link in the card and the end screen,
and the description to his construction video.
It's amazing what you can learn from watching someone
build an object like this.
So we've got this rotor plate here.
This thing weighs almost two kilograms.
And it rests on these three tilting pads,
they can tilt on these ball bearings here.
I'm gonna go off on a quick tangent.
Look happens when I lift the rotor off those pads,
the pads stick to the rotor and they eventually fall off,
that's because they're wringing together.
These surfaces are incredibly flat
to a tolerance of around 100 nanometers.
And you could do something similar with gauge blocks.
I've got a couple of gauge blocks here.
They're precision-width blocks of metal.
And so, the end phases are incredibly flat.
When you press them together,
well, they stick.
That's called gauge block wringing,
and we can see something similar here.
No one really knows for sure why gauge blocks
wring together in this way, but I'll link to a 60 symbols
video that goes into a bit more detail.
If I try and turn the rotor,
there's a decent amount of resistance,
because it's nearly two kilograms.
But watch what happens when I give it a proper spin.
Isn't that amazing?
This thing will spin over a minute,
because it's floating on a cushion of air.
A cushion of air that's about three or four microns thick,
according to Tom's calculations.
We can actually prove the thing is floating
using this device here.
This is what Tom call his Octo-continuity Checker,
and it's just a little LED light, there's a battery inside
and some cables have been drawn out
so that you can complete the circuit from the outside.
Look, there we go.
The light turns on when we complete the circuit.
So we can feed this through the bearing to see
if the circuit breaks when we spin it.
This is an insulating rod.
So if we connect the LED to the top and the bottom
and the LED turns on, we know that's because the circuit
is being completed through the bearing.
In other words the rotor is touching the pads
when it's at rest.
So let's spin up the rotor and see what happens.
There you go, the LED turns off.
As the rotor slows down, you start to see flashes of the LED
as the rotor occasionally touches the pads.
And those flashes increase as the rotor slows down,
until eventually you get a solid light and the rotor stops.
Hand-held bearings like this were built as a marketing tool
so that sales people could sell much larger versions
for use in industry like, to support a turbine
in a hydroelectric plant that might weigh hundreds of tons.
The Kingsbury Aerodynamic Bearing and the glass syringe
are examples of hydrodynamic bearings
as opposed to hydrostatic bearings.
A hydrostatic bearing involves injecting a fluid
like air into the system.
So for example, an Air Hockey Puck,
it floats on a cushion of air because air is pushed in
through holes in the air hockey table.
A hovercraft is another example.
But, a hydrodynamic bearing is self-starting,
it doesn't need an injection of fluid.
So, how is that possible?
Let's look at the glass syringe first,
and let's suppose that it's resting on its side like this.
Here's an exaggerated view of the cross-section
of the syringe, where the gap between the plunger
and the barrel is exaggerated.
You can see that the plunger is resting
on the bottom of the inside of the barrel.
When the plunger is at rest,
there's a lot of friction between the two surfaces.
But when we spin the plunger, all of that changes.
And that's because air is viscous.
Because air is viscous,
it sticks to the surface of the plunger
and it sticks to itself.
That's hard to imagine in the case of air,
it's easier to imagine in the case of something like honey,
which is a really viscous fluid.
Like, if you pressed honey between two surfaces
and then moved one of the surfaces,
you can imagine the surface dragging the honey with it,
and there'll be some resistance to motion.
Well, the same is true for air,
except that the viscosity of air
is much, much lower than honey.
But anyway, the point is, when the plunger rotates
it drags air with it.
So, as air is pulled down into this gap
by the surface of the plunger, the pressure increases.
And if you can spin the plunger fast enough,
the pressure will get high enough
to lift the plunger off from the surface of the barrel,
and it's now spinning on a cushion of air.
This isn't the intended use of a glass syringe.
And in fact, when you're building a hydrodynamic bearing
for industrial use, you're probably not gonna use air,
you're gonna use an oil or grease.
And actually, it's a balancing act with the viscosity.
You don't want the viscosity to be too low,
because then you don't get that cushion of fluid.
And you don't want the viscosity to be too high either,
because that resists the rotation of the device.
The Kingsbury bearing works in a similar way,
the surface of the rotor drags air in between the rotor
and the pads.
Because the pads are able to tilt,
they form a wedge-shaped cavity,
which I've shown in an exaggerated form here.
And it means that the air that is pulled through,
is forced into an increasingly narrow space.
Hydroplaning or aquaplaning works by a similar principle,
so does ice skating, when an ice skate runs over the ice,
it melts the ice, so you have a layer of water
between the skate and the ice.
It's also the working principle of this playing card
that I've slightly turned the end up of.
The original Hyperloop concept was based on this idea
as well, though, it isn't anymore.
So there you go, the hydrodynamic bearing
crops up in all sorts of strange places.
Thank you to Patrick Herd and a big, big thank you
to Tom Lipton for his help on this video.
Don't forget to watch his video on the subject
and the rest of his channel,
the links are in the description.
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and I'll see you next time.
(upbeat music)