Saintlysins said:
Tend to agree with the previous posts ... and to add to it ... there is only one force of gravity, and that’s where all objects will eventually end. Our vehicles do not have any natural or mechanical gravity. Any airborne particles a vehicle traveling into will NOT likely impact nor ride along the surface as the immediate rush of air along the surface of the car is significantly greater than both the gravitational force of Earth and the weight of an airborne particle. The air closest to the surface of the car is traveling at a significantly and proportionately greater speed the closer to the surface of the car than further away.
Well, gravity has no bearing on the theory of mine... what you may be talking about is the boundary layer flow of the air rushing past the surface of the car. Because no surface is perfectly frictionless, air moving along a surface will have a curvilinear velocity profile in the direction perpendicular to the surface, with the lowest velocity being near the surface. This is because surface friction is "dragging" the air slower closer to the surface than further away. However, the air velocity is never zero at the surface, and therefore particles which don't stick to the surface can get pushed along.
Saintlysins said:
If you’re to watch testing done in a wind chamber, the vapor never touches the car, and the car (or object) stays dry, at any speed. Respectfully ... using your theory, the vapor would impact the item being tested and get dragged along the surface.
While your observation is correct, the reasoning is not. The smoke particles (often made of vaporised mineral oil) are in fact so small that they are fully entrained in the flow and do not touch the surface of the object. This is why they are used for flow visualization. Particles less than about 10 microns entrained in a moving fluid such as air generally will not touch surfaces it comes across, because the pressure increase as you go towards the surface gets high enough to keep the particles away.
Saintlysins said:
Since water-vapor would certainly have a cling factor greater than a solid particle, and this doesn’t happen, this would make us lean in favor of dust and other ‘airborne contaminants’ are following the same path.
Never heard of the term "cling factor", but I'll assume that what you mean is that a fluid (water) should adhere to a surface more readily than a solid (dust). I'll agree with that, but the ipso facto statement above is not quite correct - even if a fluid or solid particle in moving air is very "sticky", if it's small enough and light enough, it will NOT stick to a surface it's moving past because the pressure gradient across the moving air increases towards the surface, and the particle will be kept away. This is the primary feature of all smoke/flow visualization media.
Saintlysins said:
The ‘dirt’ we see that does collect on the vehicles is stagnate – and adheres chemically to the surface of the car, (moisture, proteins, carbons, etc are sticky). This dirt isn’t going to migrate to the rear of the car as we drive it, as its bond is greater than the force of air going over it.
Two items here that I disagree with:
1. you'll have to show how you're sure that the "dirt" collected on car surfaces is in fact "chemically adhered" to the surface. Carbon by itself has no adhesive property. Moisture cannot be classified as dirt because they tend to evaporate and be gone eventually. Proteins? Where would these come from? Common dust that I'm talking about can be partly wiped off by mouth blowing on it hard enough. You can also experiment with a bicycle pump, and slowly pump air on a dusty car - see whether you can take off any dry dust or not. I can.
There is also a static electricity effect that makes dry dust stick to your car surface, but this is not the same as chemical bonding.
2. you'll also have to show how you are sure whether the "bond" you talk about between dust and car surface is in fact stronger than the force of air going over it - you don't mention how strong the air would be. Will a 75mph gust of air be strong enough?
Saintlysins said:
We may see streaking of filth across a car after a drive through the rain, but this doesn’t affect the paint as the water is lifting the contaminants over the surface and only leaving them behind as the water evaporates where it pooled. There are no scratches along those streaks.
Well, that is contrary to what most of the detailers here say, that dirty water going across your paint without any lubricant (e.g. ONR or car wash shampoo) is terrible for your finish.
Without any surfactants in the water (and rain water doesn't have any), any dirt that gets carried by water will not be emulsified, suspended, and dispersed, hence the dirt particles will drag along the surface and scratch. You can try this out for yourself on a painted surface (not your car!) - get a hose and drip water on the painted surface. Introduce dirt particles in the water drip and see what happens to the surface after a few tens of minutes of this - scratches!
Saintlysins said:
To break that bond we must use a force greater than the compressed wind across our vehicles, and that involves touching it with all the chemicals, tools and ‘force’ required.
I'd like to believe you, but a simple experiment with low compressed air on a dirty car will show the opposite of what you say.
Saintlysins said:
This is the point at which we’re marring, spider-webbing, and as the term implies: swirling our tools over the surface.
I totally agree with this, that touching the car surface is likely to introduce swirls.
Saintlysins said:
None of this is designed to belittle your post or theory. I’m only trying to help with a little perspective and science.
No offence taken at all. I'm happy to talk geek! However, the basis and assumption of my theory is this: dirt particles that are not small enough to be completely entrained in air are the ones that can cause light scratches - think of the analogy of water droplets being dragged across your windshield and car as you travel at speed through rain. But, as I've said many times before, my theory remains to be proven!
Actually, you've just added to my theory of dirt scratching cars as you drive - when dust/dirt gets wet, and you drive along with the water trailing the surface, that could be another mechanism for scratching! Cheers
