Elliptical oil drops

[G.Daniels]

elliptical oil ring on the road.. celestial bodies not a member of the set of all stone houses bi cy
cl e s?..................................................... l l l l l l
~~~~~~~~~~~~~~~~~~~~

??

 

[Ken Bessler]

"g.daniels" <[email protected]> wrote in message
news:[email protected]...
> elliptical oil ring on the road.. celestial bodies not a member of the set of all stone houses bi
> cy cl e s?..................................................... l l l l l l
>
~~~~~~~~~~~~~~~~~~~~
>
> ??

I'll take some of what he's having........

 

[Jobst Brandt]

Dan Parks writes:

>> Unfortunately the last drawing in this URL, the drop should have a line across the bottom,
>> showing that it is the cross section of a nearly a complete "soap bubble". Soap bubble leave a
>> wet ring on the surface where they land. If that surface is moving relative to the bubble, the
>> ring will be elliptical.

>> The unanswered question that I have is, why they all have nearly the same aspect ratio of major
>> to minor axis, regardless of size. They range from 20 to 200mm in length. It means that they all
>> have the same velocity to the road when they burst, but why?

> It does seem that the rings might be due to the detritus of bubbles that had burst in the air
> instead of on impact. (If this is what you meant all along, then color me slow.) Seeing as that a
> ring of oil trailing a bubble parachute would be a very unstable thing, it is very possible that
> these bubbles always burst upon attaining about the same velocity. A splatter of small spherical
> droplets then form the ring patterns seen.

Not so. A soap bubble leaves a wet ring on the floor when it makes contact and bursts. The raindrop
picture is not complete because the ring at the neck of the forming bubble with thick cross section
(it is a ring although not correctly drawn) has sufficient surface tension to close the bubble. It
is this bubble (of oil) that strikes the ground, bursts and leaves a ring.

> I can imagine two failure modes of the bubble structure. One is the approximately radially
> symmetric failure of the bubble parachute. This produces a cylindrically symmetric spray of
> droplets. The other is an instability in the ring that results in thinning of one side of the
> ring. This leads to a rupture of the ring and most of the mass ending up in one side of the ring.
> (results in a half ellipse?)

Neither of these scenarios would produce a closed ellipse. Some open ended ellipses are found on
roads, but don't support your incomplete bubble model because it is the trailing end (in direction
of vehicle motion) that is open.

Jobst Brandt [email protected]

 

[Jobst Brandt]

John Albergo <[email protected]> writes:

>> Unfortunately the last drawing in this URL, the drop should have a line across the bottom,
>> showing that it is the cross section of a nearly a complete "soap bubble". Soap bubble leave a
>> wet ring on the surface where they land. If that surface is moving relative to the bubble, the
>> ring will be elliptical.

>> The unanswered question that I have is, why they all have nearly the same aspect ratio of major
>> to minor axis, regardless of size. They range from 20 to 200mm in length. It means that they all
>> have the same velocity to the road when they burst, but why?

> Assuming that most oils have the same surface tension, then I'd guess that most oil drips would be
> about the same size, and "pop" at about the same airspeed (relative wind). Perhaps the size of the
> resulting road ring is due to the "altitude" of the burst?

After thinking about it some more and looking at oil drops on Sierra mountain passes this weekend, I
am convinced by the number of oil splotches and oil mist on roads that the oil bubble forms only in
a narrow range of wind speed. Wind speed being vehicle speed. These ellipses are formed relatively
rarely in the genersal environment of vehicle oil drips. That seems the most reasonable conclusion I
can find. High seed routes have only oil fog. Driveways, only drops.

Jobst Brandt [email protected]

 

[Jobst Brandt]

Tim McNamara writes:

>> The unanswered question that I have is, why they all have nearly the same aspect ratio of major
>> to minor axis, regardless of size. They range from 20 to 200mm in length. It means that they all
>> have the same velocity to the road when they burst, but why?

> Terminal velocity of an oil droplet? If the car is going too fast, the oil atomizes and if going
> too slow, it leaves a blob rather than a ring?

I agree.

Jobst Brandt [email protected]

 

[Jobst Brandt]

Sergio Servadio writes:

> I am not to blame. Because our local connection had problems, I was able to read the beginning of
> this 'story' and a few posts of the thread, but not the whole thread. For me, and benefit of
> others, how about having someone make a resume and play the moderator? Why not you, Jobst?

For those with average computer connections, we seem to be doing just fine. The last thing I want to
do is be moderator in this tech newsgroup because, as you may have noticed, I have little patience
with much of the "technical inaccuracies" put forth here as fact.

However, You could pass the original question on to your colleagues at UniPi; Aerodynamics, Fluids,
Physics and others, without giving any hints to the answer. That would be much more interesting and
exchanging views here on wreck.bike.

Jobst Brandt [email protected]

 

[Sergio Servadio]

On Mon, 15 Sep 2003 [email protected] wrote:
> After thinking about it some more and looking at oil drops on Sierra mountain passes this
> weekend, ...

Let me throw in a couple of thoughts of mine, whether new to you or not.

You say you see them on mountain roads. That might be the clue to the elliptical, rather than the
circular, shape: gravity, independently of the (necessarily slow) speed of the parent vehicle.

Why a circular or elliptical ring, whereas most spots are just full circles or ellipses? I was
thinking of a vehicle dripping oily water from the cooling system or watery oil from the engine.
Then, after getting onto the asphalt, surely thy oil migrates to the rim, survives evaporation of
the inner watery part and there you see it.

Sergio Pisa

 

[Bruce Hollebone]

On 13 Sep 2003, John Albergo wrote:

> Assuming that most oils have the same surface tension...

Parathentically aside: they do. Most oils, inlcuding motor oils and common lubes, have surface
tensions between 25-30 mN/m.

--
Kind Regards, Bruce.

 

[G.Daniels]

III +()+? ..................................................... recent equations suggest vehicle
dynamics.NO? l newton never went to the sea? but newton lived on the river? l Burroughs was an 11
mile hike from stonehenge. l did not walk over.amazing.

l mysteries equal to the post's subject. a metaphor for...? Arnold and the mystery government?
i'm gonna quantify my entry!! and hold up an applewood branch and shout... l g=F/m E=E/q g=F/m
F=Ma F=Ma E=E/q !!!!!!!eeeeeeyah!!!! l l l l

 

[Jobst Brandt]

Sergio Servadio writes:

>> After thinking about it some more and looking at oil drops on Sierra mountain passes this
>> weekend, ...

> Let me throw in a couple of thoughts of mine, whether new to you or not.

> You say you see them on mountain roads. That might be the clue to the elliptical, rather than the
> circular, shape: gravity, independently of the (necessarily slow) speed of the parent vehicle.

I suggest you look at the pictures of such drops that Dave has posted:

http://www.mindspring.com/~darsal/droplets/ell1-med.jpg
http://www.mindspring.com/~darsal/droplets/family.jpg

> Why a circular or elliptical ring, whereas most spots are just full circles or ellipses?

They are all over the roads in your area as well. If you looked at them, you would probably arrive
at a different scenario. However, if you look at the course of this thread, the answers have fairly
well been arrived upon. That is why I suggest you present this to your scientific colleagues for
assessment.

> I was thinking of a vehicle dripping oily water from the cooling system or watery oil from the
> engine. Then, after getting onto the asphalt, surely thy oil migrates to the rim, survives
> evaporation of the inner watery part and there you see it.

These are oil drops. I have seen them in white paint spilling from a painter's truck and in tar from
a hot tar roofing kettle, the kind that is often a trailer with heater. These are probably the best
ones but rare because most roofing companies don't leave their kettle dripping in transit and there
are not too many of them on slow roads.

http://www.reevesequipment.com/EquipCatalog/afterburnernf.htm

Jobst Brandt [email protected]

 

[Dan]

> Not so. A soap bubble leaves a wet ring on the floor when it makes contact and bursts.

Is this a burst upon point contact or after the bubble has settled on the floor? Typically bubbles
that do not burst on point contact settle into a hemisphere configuration and then burst.

> The raindrop picture is not complete because the ring at the neck of the forming bubble with thick
> cross section (it is a ring although not correctly drawn) has sufficient surface tension to close
> the bubble. It is this bubble (of oil) that strikes the ground, bursts and leaves a ring.

Can you point me to a reference? Otherwise this is only true by assertion.

While there may be sufficient surface tension to close the bubble, is there sufficient time? It is
difficult to state what the surface tension really is considering the material is in general a
contaminated oil at an undetermined temperature.

>
> > I can imagine two failure modes of the bubble structure. One is the approximately radially
> > symmetric failure of the bubble parachute. This produces a cylindrically symmetric spray of
> > droplets. The other is an instability in the ring that results in thinning of one side of the
> > ring. This leads to a rupture of the ring and most of the mass ending up in one side of the
> > ring. (results in a half ellipse?)
>
> Neither of these scenarios would produce a closed ellipse.

A directed spray of droplets from a cylindrically symmetric source could well produce a closed
ellipse on the ground.

> Some open ended ellipses are found on roads, but don't support your incomplete bubble model
> because it is the trailing end (in direction of vehicle motion) that is open.
>

I didn't say which end would open, trailing or leading. I fail to see how this model is excluded
based solely on the observation that it is the trailing end that is open.

Yes, you are right, this discussion really belongs in a different forum. Perhaps I'll see you there.

 

[Tim McNamara]

In article <[email protected]>, [email protected] wrote:

> Tim McNamara writes:
>
> >>> Otherwise I couldn't descend leaning over near 45 degrees as I often do on smooth roads.
>
> >> Help me understand:
>
> >> Would it be in the right ballpark to say that riding (cornering, right?) at 45 degrees lean is
> >> about the same as riding straight and upright across about a 35 degree tilted surface?
>
> > Track sprinters ride on a 40 to 50 degree banked surface down to walking speeds. Our local
> > velodrome is wood with a 43 degree pitch in the corners and I've ridden that down to about 11-12
> > mph before my nerves took over. Below about 14 mph, pedal strikes become much more likely.
>
> Not true. You can easily disprove that by seeing at what angle your pedal will ground. It is
> nowhere near 40 degrees. This is one of the ways for beginners to crash on a track. They roll into
> the curve at to low a speed.

Hmmm, I don't quite follow this so let me ask for clarification.

One can ride to a standstill on the banking and not fall off (I believe you have posted that you
have done this with a road bike on a velodrome, and I've seen it done by sprinters). Traction isn't
the limiter here. As long as one doesn't hit the uptrack pedal and lift the rear wheel off the
track, one should stick to it just fine.

I have twice been involved in crashes when a rider in front of me struck a pedal and went down,
taking me with them. In both cases this was rolling out for the points race, at an overly slow speed
(about 12 mph) and the leading rider failing to slightly lean the bike to the inside to provide
pedal clearance on the uptrack side. Is that what you were referring to- maximum lean angle being
under 40 degrees relative to the surface?

My track bike, with 165 mm cranks, narrow track pedals and a high bottom bracket comes pretty close
to 40 degrees in terms of lean angle, guesstimating from looking at it. However, the local velodrome
is banked at 43 degrees in the corners, hence the problems with pedal strikes. IME, as the rider
gets above walking pace there is more of a natural inclination to lean to the inside in corners but
at slower speeds the inexperienced track rider tends to ride like they're in a parking lot- vertical
and steering with large handlebar movements.

 

[Jobst Brandt]

Tim McNamara <[email protected]> writes:

>>>> Help me understand:

>>>> Would it be in the right ballpark to say that riding (cornering, right?) at 45 degrees lean is
>>>> about the same as riding straight and upright across about a 35 degree tilted surface?

Yes...

>>> Track sprinters ride on a 40 to 50 degree banked surface down to walking speeds. Our local
>>> velodrome is wood with a 43 degree pitch in the corners and I've ridden that down to about 11-12
>>> mph before my nerves took over. Below about 14 mph, pedal strikes become much more likely.

>> Not true. You can easily disprove that by seeing at what angle your pedal will ground. It is
>> nowhere near 40 degrees. This is one of the ways for beginners to crash on a track. They roll
>> into the curve at to low a speed.

> Hmmm, I don't quite follow this so let me ask for clarification.

> One can ride to a standstill on the banking and not fall off (I believe you have posted that you
> have done this with a road bike on a velodrome, and I've seen it done by sprinters). Traction
> isn't the limiter here. As long as one doesn't hit the uptrack pedal and lift the rear wheel off
> the track, one should stick to it just fine.

Track bikes have no freewheel, so the cranks rotate all the time. With the pedal on your bicycle
(toe-clip pedals) at the bottom of the stroke, lean the bicycle until the pedal touches the ground.
This is the angle of the track at which the rider will fall if traveling at near zero speed.

> I have twice been involved in crashes when a rider in front of me struck a pedal and went down,
> taking me with them. In both cases this was rolling out for the points race, at an overly slow
> speed (about 12 mph) and the leading rider failing to slightly lean the bike to the inside to
> provide pedal clearance on the uptrack side. Is that what you were referring to- maximum lean
> angle being under 40 degrees relative to the surface?

I am referring to the angle, on flat ground, that a bicycle can lean while pedaling, without
grounding a pedal. Leaning the bicycle out from under the rider on a track is a last ditch effort
and does not work reliably for continuous riding on a steeply banked track.

> My track bike, with 165 mm cranks, narrow track pedals and a high bottom bracket comes pretty
> close to 40 degrees in terms of lean angle, guesstimating from looking at it. However, the local
> velodrome is banked at 43 degrees in the corners, hence the problems with pedal strikes. IME, as
> the rider gets above walking pace there is more of a natural inclination to lean to the inside in
> corners but at slower speeds the inexperienced track rider tends to ride like they're in a parking
> lot- vertical and steering with large handlebar movements.

The concept of lean angle in cornering, whether on foot, roller skates or motorcycle is well
understood. The angle from the vertical is ATN(R*w^2) [R: turn radius, w: angular velocity in
radians]. The track is banked so that the angle between a rider and the track, at full speed, is
near perpendicular. The idea is to offer the effects of a straight infinitely long track while
remaining in the confines of the oval. This is the same for running tracks.

Jobst Brandt [email protected]

 

[Rick Onanian]

On Wed, 17 Sep 2003 21:21:29 -0500, Jim Adney <[email protected]> wrote:
> I thought sure that I found it last night, but, if so, that post has expired off my newsreader
> by today.

groups.google.com is your friend.

> So someone marketed elliptical chainrings under the tradename Thetic? What era was this? I'm
> already aware that elliptical chainrings have

1930s, I think.

> gone periodically in and out of style for over 100 years. I just never heard the Trade name Thetic
> used before.

Me neither.

> -
> -----------------------------------------------
> Jim Adney [email protected] Madison, WI 53711 USA
> -----------------------------------------------
--
Rick Onanian

 

[Tim McNamara]

In article <[email protected]>, [email protected] wrote:

> The track is banked so that the angle between a rider and the track, at full speed, is near
> perpendicular. The idea is to offer the effects of a straight infinitely long track while
> remaining in the confines of the oval

Yes, this was of course noticeable when riding the track. And I think you just explained why the
headsets on my track bike developed indents much more quickly than my road bikes.

 

[Mike Murray]

<[email protected]> wrote: " The track is banked so that the angle between a rider and
the track, at full speed, is near perpendicular. The idea is to offer the effects of a straight
infinitely long track while remaining in the confines of the oval."

Actually this is not correct. A track that is banked so that it makes the rider perpendicular at
full speed will be banked too steeply most of the time. The bank needs to be constructed so that it
is steep enough that the rider will be able to ride at full speed without hitting an inside pedal or
having significant force sliding them up track but they should not be perpendicular at full speed.
Alpenrose Velodrome has a steep bank, probably steeper than is needed, but the rider will be
perpendicular at only 23 mph.
--
Mike Murray

 

[Jobst Brandt]

Mike Murray writes:

>> The track is banked so that the angle between a rider and the track, at full speed, is near
>> perpendicular. The idea is to offer the effects of a straight infinitely long track while
>> remaining in the confines of the oval.

> Actually this is not correct. A track that is banked so that it makes the rider perpendicular at
> full speed will be banked too steeply most of the time.

"near perpendicular" means NOT perpendicular. The variation from perpendicular depends on rider
speed. Cruising in a team race or at maximum speed puts the lean angle either side of perpendicular,
the bias of the track angle being toward the higher speed, since this is the important one.

Jobst Brandt [email protected]

 

[John Albergo]

--------------060007010502090105080204 Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Transfer-Encoding: 7bit

[email protected] wrote:

>John Albergo <[email protected]> writes:
>
>
>
>>>Unfortunately the last drawing in this URL, the drop should have a line across the bottom,
>>>showing that it is the cross section of a nearly a complete "soap bubble". Soap bubble leave a
>>>wet ring on the surface where they land. If that surface is moving relative to the bubble, the
>>>ring will be elliptical.
>>>
>>>
>
>
>
>>>The unanswered question that I have is, why they all have nearly the same aspect ratio of major
>>>to minor axis, regardless of size. They range from 20 to 200mm in length. It means that they all
>>>have the same velocity to the road when they burst, but why?
>>>
>>>
>
>
>>Assuming that most oils have the same surface tension, then I'd guess that most oil drips would be
>>about the same size, and "pop" at about the same airspeed (relative wind). Perhaps the size of the
>>resulting road ring is due to the "altitude" of the burst?
>>
>>
>
>After thinking about it some more and looking at oil drops on Sierra mountain passes this weekend,
>I am convinced by the number of oil splotches and oil mist on roads that the oil bubble forms only
>in a narrow range of wind speed. Wind speed being vehicle speed. These ellipses are formed
>relatively rarely in the genersal environment of vehicle oil drips. That seems the most reasonable
>conclusion I can find. High seed routes have only oil fog. Driveways, only drops.
>
>

After further reflection I think the error is in thinking of these in terms of soap bubbles. From
the diagram presented earlier, the air-buffeted droplet forms a ring, with a thinner "parachute"
at the back that provides cohesion and pulling force against the ring closing. This is unlike a
soap bubble that has relatively uniform thickness because it has escaped the turbulence that
formed it and claimed a spherical shape. I think the oil bubble in question is not allowed to
complete the sphere.

Further, the relative wind experienced by the droplet is coming from the direction of travel. So I
can see the resulting ring oriented more nearly vertical to the road. If this object settles with
some forward velocity you get an eliptical ring. The thin film forming the parachute would either
break and retreat to the ring from surface tension, or perhaps deposit on the road but its much
lower mass would leave a much fainter mark. I'd guess that parachute breakage at impact would be
common. The ring itself would last longer under those conditions, perhaps long enough to deposit the
elipse. On those occasions where the ring lost cohesion before complete deposition, you would get
the open-ended elipse you've observed with the opening in the direction of travel.

Instead of my altitude-burst hypothesis I now think the various sizes are simply caused by the
amount of inflation of the object prior to contact. The previous idea was based again on soap
bubbles and the idea that an equivalent mass of soapy water would yield bubbles of about the
same size. however, with the object we're talking about, the predominant mass can be contained
in the annular ring, and more can be pulled into the parachute, and the ring opening expanded to
various sizes.

finally, the uniform ratio of length and width suggests *settling* at a fairly uniform forward
speed, and this should be caclulable by assuming a reasonable fall height for the drop, giving the
vertical acceleration. It seems that would be a fairly low forward speed. The forward speed will
have degraded significantly once the drop hits the oncoming wind. It is probably the initial
encounter with the airstream that determines whether the drop is volatized, remains a drop, or
forms the ring/parachute. Figuring that initial airspeed from the elipse I KNOW takes more math
than I have.

Now that I've hedged my bets with contradictory hypotheses some testing is in order. I don't know if
I can generate enough windspeed with my household fans though I'll probably give it a shot. Perhaps
someone with a leafblower would like to try. My other option would seem to be deliberately dripping
oil from a moving vehicle, which would probably get me a citation as opposed to the millions of
"honest" oil drippers. My preference would be a stationary test and try to get some images or at
least some oil rings on a newspaper.

>
>

--------------060007010502090105080204 Content-Type: text/html; charset=us-ascii
Content-Transfer-Encoding: 7bit

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta
http-equiv="Content-Type" content="text/html;charset=ISO-8859-1"> <title></title> </head> <body>
<br> <br> <a class="moz-txt-link-abbreviated"
href="mailto:[email protected]">[email protected]</a> wrote:<br>
<blockquote type="cite" cite="[email protected]"> <pre wrap="">John
Albergo <a class="moz-txt-link-rfc2396E"
href="mailto:[email protected]"><[email protected]></a> writes:

</pre> <blockquote type="cite"> <blockquote type="cite"> <pre wrap="">Unfortunately the last
drawing in this URL, the drop should have a line across the bottom, showing that it is the cross
section of a nearly a complete "soap bubble". Soap bubble leave a wet ring on the surface where
they land. If that surface is moving relative to the bubble, the ring will be elliptical. </pre>
</blockquote> </blockquote> <pre wrap=""><!----> </pre> <blockquote type="cite"> <blockquote
type="cite"> <pre wrap="">The unanswered question that I have is, why they all have nearly the
same aspect ratio of major to minor axis, regardless of size. They range from 20 to 200mm in
length. It means that they all have the same velocity to the road when they burst, but why? </pre>
</blockquote> </blockquote> <pre wrap=""><!----> </pre> <blockquote type="cite"> <pre
wrap="">Assuming that most oils have the same surface tension, then I'd guess that most oil drips
would be about the same size, and "pop" at about the same airspeed (relative wind). Perhaps the
size of the resulting road ring is due to the "altitude" of the burst? </pre> </blockquote> <pre
wrap=""><!----> After thinking about it some more and looking at oil drops on Sierra mountain
passes this weekend, I am convinced by the number of oil splotches and oil mist on roads that the
oil bubble forms only in a narrow range of wind speed. Wind speed being vehicle speed. These
ellipses are formed relatively rarely in the genersal environment of vehicle oil drips. That seems
the most reasonable conclusion I can find. High seed routes have only oil fog. Driveways, only
drops. </pre> </blockquote> <blockquote type="cite"
cite="[email protected]"> </blockquote> <pre wrap="">

After further reflection I think the error is in thinking of these in terms of soap bubbles. From
the diagram presented earlier, the air-buffeted droplet forms a ring, with a thinner "parachute" at
the back that provides cohesion and pulling force against the ring closing. This is unlike a soap
bubble that has relatively uniform thickness because it has escaped the turbulence that formed it
and claimed a spherical shape. I think the oil bubble in question is not allowed to complete the
sphere.</pre> Further, the relative wind experienced by the droplet is coming from the direction of
travel. So I can see the resulting ring oriented more nearly vertical to the road. If
this object settles with some forward velocity you get an eliptical ring. The thin film
forming the parachute would either break and retreat to the ring from surface tension, or perhaps
deposit on the road but its much lower mass would leave a much fainter mark. I'd guess that
parachute breakage at impact would be common. The ring itself would last longer under those
conditions, perhaps long enough to deposit the elipse. On those occasions where the ring lost
cohesion before complete deposition, you would get the open-ended elipse you've observed with the
opening in the direction of travel.<br> <br> Instead of my altitude-burst hypothesis I now think
the various sizes are simply caused by the amount of inflation of the object prior to contact.
The previous idea was based again on soap bubbles and the idea that an equivalent mass of
soapy water would yield bubbles of about the same size. however, with the object we're
talking about, the predominant mass can be contained in the annular ring, and more can be pulled
into the parachute, and the ring opening expanded to various sizes.<br> <br> finally, the uniform
ratio of length and width suggests *settling* at a fairly uniform forward speed, and this should be
caclulable by assuming a reasonable fall height for the drop, giving the vertical acceleration.
It seems that would be a fairly low forward speed. The forward speed will have degraded
significantly once the drop hits the oncoming wind. It is probably the initial encounter with
the airstream that determines whether the drop is volatized, remains a drop, or forms the
ring/parachute. Figuring that initial airspeed from the elipse I KNOW takes more math than I
have.<br> <br> Now that I've hedged my bets with contradictory hypotheses some testing is in order.
I don't know if I can generate enough windspeed with my household fans though I'll probably
give it a shot. Perhaps someone with a leafblower would like to try. My other option
would seem to be deliberately dripping oil from a moving vehicle, which would probably get me a
citation as opposed to the millions of "honest" oil drippers. My preference would be a
stationary test and try to get some images or at least some oil rings on a newspaper.<br> <br> <br>
<blockquote type="cite" cite="[email protected]"> <pre wrap=""> </pre>
</blockquote> <br> </body> </html>

--------------060007010502090105080204--

 

[Jobst Brandt]

John Albergo writes:

>>>> Unfortunately the last drawing in this URL, the drop should have a line across the bottom,
>>>> showing that it is the cross section of a nearly a complete "soap bubble". Soap bubble leave a
>>>> wet ring on the surface where they land. If that surface is moving relative to the bubble, the
>>>> ring will be elliptical.

>>>> The unanswered question that I have is, why they all have nearly the same aspect ratio of major
>>>> to minor axis, regardless of size. They range from 20 to 200mm in length. It means that they
>>>> all have the same velocity to the road when they burst, but why?

>>> Assuming that most oils have the same surface tension, then I'd guess that most oil drips would
>>> be about the same size, and "pop" at about the same airspeed (relative wind). Perhaps the size
>>> of the resulting road ring is due to the "altitude" of the burst?

>> After thinking about it some more and looking at oil drops on Sierra mountain passes this
>> weekend, I am convinced by the number of oil splotches and oil mist on roads that the oil bubble
>> forms only in a narrow range of wind speed. Wind speed being vehicle speed. These ellipses are
>> formed relatively rarely in the general environment of vehicle oil drips. That seems the most
>> reasonable conclusion I can find. High seed routes have only oil fog. Driveways, only drops.

> After further reflection I think the error is in thinking of these in terms of soap bubbles. From
> the diagram presented earlier, the air-buffeted droplet forms a ring, with a thinner "parachute"
> at the back that provides cohesion and pulling force against the ring closing. This is unlike a
> soap bubble that has relatively uniform thickness because it has escaped the turbulence that
> formed it and claimed a spherical shape. I think the oil bubble in question is not allowed to
> complete the sphere.

Hold it. There is no evidence whatsoever that a drop forms a ring. As you see, even a water drop
forms a bubble. This bubble usually breaks and leaves a ring of tiny droplets. With oil (or soapy
water) the bubble does not break and the neck of the bubble closes from surface tension. These
bubbles have been photographed and is on what the rain drop web page is based.

> Further, the relative wind experienced by the droplet is coming from the direction of travel. So I
> can see the resulting ring oriented more nearly vertical to the road. If this object settles with
> some forward velocity you get an elliptical ring. The thin film forming the parachute would either
> break and retreat to the ring from surface tension, or perhaps deposit on the road but its much
> lower mass would leave a much fainter mark. I'd guess that parachute breakage at impact would be
> common. The ring itself would last longer under those conditions, perhaps long enough to deposit
> the ellipse. On those occasions where the ring lost cohesion before complete deposition, you would
> get the open-ended ellipse you've observed with the opening in the direction of travel.

Your hypothesis is based on the "ring" theory which is contrary to experimental and logical results.

> Instead of my altitude-burst hypothesis I now think the various sizes are simply caused by the
> amount of inflation of the object prior to contact. The previous idea was based again on soap
> bubbles and the idea that an equivalent mass of soapy water would yield bubbles of about the
> same size. however, with the object we're talking about, the predominant mass can be contained
> in the annular ring, and more can be pulled into the parachute, and the ring opening expanded to
> various sizes.

These bubbles burst when contacting the road.

> finally, the uniform ratio of length and width suggests *settling* at a fairly uniform forward
> speed, and this should be calculable by assuming a reasonable fall height for the drop, giving the
> vertical acceleration. It seems that would be a fairly low forward speed. The forward speed will
> have degraded significantly once the drop hits the oncoming wind. It is probably the initial
> encounter with the air stream that determines whether the drop is volatized, remains a drop, or
> forms the ring/parachute. Figuring that initial airspeed from the ellipse I KNOW takes more math
> than I have.

Well, I disproved that theory recently by finding ellipses with as much as a 6:1 ratio as well as
2:1 ratio although they are not common among oil ellipses.

> Now that I've hedged my bets with contradictory hypotheses some testing is in order. I don't know
> if I can generate enough wind speed with my household fans though I'll probably give it a shot.
> Perhaps someone with a leaf blower would like to try. My other option would seem to be
> deliberately dripping oil from a moving vehicle, which would probably get me a citation as opposed
> to the millions of "honest" oil drippers. My preference would be a stationary test and try to get
> some images or at least some oil rings on a newspaper.

I doubt it. The household fan is to slow and creates too much turbulence. You'll need to build a
laminar wind tunnel. Besides, what you are testing has all been done.

Jobst Brandt [email protected]

 

[Jobst Brandt]

John Albergo writes:

>>> After further reflection I think the error is in thinking of these in terms of soap bubbles.
>>> From the diagram presented earlier, the air-buffeted droplet forms a ring, with a thinner
>>> "parachute" at the back that provides cohesion and pulling force against the ring closing. This
>>> is unlike a soap bubble that has relatively uniform thickness because it has escaped the
>>> turbulence that formed it and claimed a spherical shape. I think the oil bubble in question is
>>> not allowed to complete the sphere.

>> Hold it. There is no evidence whatsoever that a drop forms a ring. As you see, even a water drop
>> forms a bubble. This bubble usually breaks and leaves a ring of tiny droplets. With oil (or soapy
>> water) the bubble does not break and the neck of the bubble closes from surface tension. These
>> bubbles have been photographed and is on what the rain drop web page is based.

> To be clear, I wasn't envisioning a ring such as a smoke-ring, but a 3D representation of what
> appears on the "bad rain" page - an annular ring supported by a "parachute" film, or an unclosed
> bubble, if you will.

As I mentioned, that scenario would leave a different pattern, the open end of the "soap bubble
having a thick ring. When these marks on the road are fresh, they are thin lines, that for the
wetting ability of oil, turns into the blurred fat lines in the pictures. The ellipses are usually
uniform in line width and thin, something the parachute model would not produce in my estimation.

> I'm trying to reconcile these shapes with what has been described and photographed on the road.
> When I allow soap bubbles to settle on a smooth surface (car hood), it results in a wetted area
> that is circular and the entire area is wet, not just the circumference. I can see it forming an
> ellipse if in motion, but why wouldn't this be a filled ellipse? The idea of the unclosed bubble
> appealed since it seemed to provide a better mechanism of concentrating the liquid in an annular
> shape and therefore more promising to yield a ring-shaped stain.

It's too bad that the rain drop web site didn't have some high speed photography of the bubble
development. I believe the collar closes, there being no more pressure keeping it open once the
bubble is beginning to form. My experience is that a bursting soap bubble leaves a speckled ring on
the floor when it lands. If it does not burst (because the surface is wet) it lands and remain on
the surface as a hemisphere until it bursts.

> I understand that the surface tension in a plain water droplet is too high for a stable bubble,
> and lowering the tension with with soap allows bubble formation.

I think that it is more a function of film strength and that surface tension less important in soap
bubble formation. As you see, bubbles made by a fairly large soap bubble hoop of as much and more
than a four inch diameter produce closed bubbles. The balloon naturally closes as it necks down from
surface tension, It is this mechanism that I see as the way oil bubbles are formed.

> I'm not sure where in between oil lies, and how that influences the evolution of the shape, what
> percentage of drops actually begin to inflate/at what speeds/and the percentage of "successful vs
> unsuccessful" bubbles. When trying to blow a bubble with motor oil (SAE 30), I find I can't get it
> to sustain a film of much more than .5cm within a wire loop. To me this suggests a rather low
> "bubble potential" compared to soap film, which can stretch to areas measured in square meters.

Are you suggesting that these rings are not caused by a bubble mechanism?

> http://www.bubblething.com/

> I haven't tried hot motor oil so perhaps it has better bubble properties.

>>> Instead of my altitude-burst hypothesis I now think the various sizes are simply caused by the
>>> amount of inflation of the object prior to contact. The previous idea was based again on soap
>>> bubbles and the idea that an equivalent mass of soapy water would yield bubbles of about the
>>> same size. however, with the object we're talking about, the predominant mass can be contained
>>> in the annular ring, and more can be pulled into the parachute, and the ring opening expanded to
>>> various sizes.

This does not fit with soap bubble generation. And as you may be aware, such bubbles close naturally
after inflation, especially when there is no hoop ion which it grows.

>> These bubbles burst when contacting the road.

> That seems right, but it's not clear to me that a spherical bubble can leave an annular stain.
> From my observations of small soap bubbles they don't, but the mechanism for breakup of other
> types of bubble material could be different. It would seem that the strength of the surface
> tension would be important. With very large soap bubbles (a la 'bubble thing'), one can actually
> see the film retreating and a large portion of the mass remains contiguous but the resulting shape
> is always chaotic.

With normal soap bubbles made by a one inch wetted ring, the bursting bubble often leaves a ring. I
guess I'll have to get a soap bubble kit at Walgreen's and see what else I can find.

> However the tendency seems to be that the film retreats from the point of rupture and attempts to
> contract all the way to the antipode. A higher surface tension would seem to result in a more
> atomized dispersion as the surface tension would dominate.

> Since we're talking about rough roads I'm thinking maybe my car-hood experiments could be biased
> somehow by other effects. I tried it on rougher surfaces but wasn't able to see much -there's not
> a lot of mass in a bubble. I think I'll try again on some rough material by adding food color to
> the soap so I can see the results. But this leads to another issue I have with the observed
> phenomenon -- I'm having trouble reconciling the size and distinctness of these rings with the
> mass of an oil droplet especially since most roads already have a certain amount of oil already.
> Is it possible the rings grow over time once deposited, accumulate more oil from their
> surroundings, or even that there is some other phenomenon at work altogether? That these are
> described as being more predominant on grades is interesting also. What else other than speed is
> influenced by the grade? Coolant reservoirs overflowing? A drop of hot coolant hits the road, and
> what -- "asphalt chromatography"? Sorry for babbling, but I'm just not satisfied with the
> theories yet.

Have you found any of these ellipses on the road and if so, did you find any fresh ones, ones that
are sharp and thin lined? When you see them, I believe, some of your models will not meet the
challenge of what you find.

>>> Now that I've hedged my bets with contradictory hypotheses some testing is in order. I don't
>>> know if I can generate enough wind speed with my household fans though I'll probably give it a
>>> shot. Perhaps someone with a leaf blower would like to try. My other option would seem to be
>>> deliberately dripping oil from a moving vehicle, which would probably get me a citation as
>>> opposed to the millions of "honest" oil drippers. My preference would be a stationary test and
>>> try to get some images or at least some oil rings on a newspaper.

>> I doubt it. The household fan is to slow and creates too much turbulence. You'll need to build a
>> laminar wind tunnel. Besides, what you are testing has all been done.

> I just can't seem to find any of these photographic images online, though there are some books
> referenced that I might check. Interestingly, one of the researchers did a comparable test on oil,
> and the difference that surface tension made is described

That is a problem. We may have to wait.

Jobst Brandt [email protected]