How Does Dust Collect On Fast-Moving Objects?
I know I could just look this up, but I like reading what others on here have to say.
I clean my freaking ceiling fans about once a week and they are always on and always coated with dust.
Is this some kind of static electricity issue?
What’s the Dope?
A moving object has a thin layer of still air on its surface so accumulated dust won’t be blown off. Otherwise, they accumulate the same amount of dust as anything else. It’s the same reason a mosquito can stay on your car windshield if you’re doing 70. A fluid dynamics expert may come along if you require excrutiating detail.
The same way rain still hits your car when you’re driving.
While this response makes me feel like I asked an extraordinarily stupid question ( 
), the reason behind asking is that my house seems to be incredibly dusty. The non-moving objects collect dust at a pretty fast rate, which I understand that the dust is “falling” onto them.
The fans however, which always are on at the highest setting, accumulate dust faster than the tables, desks, etc.
I guess I thought that dust was always a “falling” object, being heavier than air and subject to gravity, and I assumed that ceiling fans would only collect dust when not in operation, as my assumption followed that the fan blades would simply move the dust motes away from them.
I know, assuming and all. I still thought it was worth asking because I wanted to understand the physics behind it.
Well, the moving objects are actually hitting more dust particles than the non moving objects, especially since they are sucking and blowing (ha!) the air through them.
Now, assume that each airborne particle has a Stickiness Quotient to it, its propensity to stick to something that it hits. Those with a low SQ will be much less likely to stick to the fan, but those with a high SQ will be very likely to stick to the fan, since despite its high velocity it is coming into contact with these particles much more often. So the cabinets etc. will accumulate those with a low SQ while the fan sucks up basically all the particles with a low SQ.
At least it seems that way to me: the dust seems a lot harder to wipe off a fan than an immobile object, and it seems that it’s because the stuff that could be easily wiped off would already have been thrown off by the fan.
I’d assume the opposite – dust can be wafted upwards by air currents, such as the ones coming from your fans. If your fans were off and the air was still, the dust would probably stay wherever it fell. Your fans may be dirty because they disturbed the dust that was lying around your house.
Yeah, I think I’m generating more dust by using the fans than by not, but I can’t help it, I love fans and moving air.
I suppose the other poster that mentioned a “stickiness” quotient in dust particles makes sense, especially in light of the fact that as the dust accumulates along the edge of the blade of the fan it seems to speed up once a decent amount of it is on there. So what makes them sticky? Moisture? Cigarette smoke? Are they naturally sticky?
Sorry, I really didn’t mean it that way. :smack:
It’s a combination of everything the previous posters have said, though.
When you’re dealing with fluids, it doesn’t matter if the object is moving through the air or the air is moving past the object (that’s why wind tunnels work). The boundary layer CookingWithGas speaks of, IIRC, is pretty small, less than a millimeter, but it’s probably important once the dust particle gets close enough to utilize the SQ Ludovic theorized. Also, as he mentions, there’s more air moving past the fan than anywhere else in the room, therefore there’s more dust moving past the fans than anything else in the room. In my first post, I was trying to make the analogy in your mind between a car moving through the rain and dust moving past your fan.
Why are they sticky? Most substances have some degree of adhesion to each other, and dust to a fan blade is probably a mixture of mechanical, dispersive, and/or electrostatic. Also, the dust builds up faster when there’s a bit of dust already because dust is more cohesive than it is adhesive to the blades. For an example of this, just think of the dust bunnies you get when you force the dust together with a rag (wiping it with a rag).
Here’s a couple wiki articles if you’re interested:
Thanks for that. I just actually Wiki’d “dust” and am a bit grossed out by the fact that they state that 70-90% of dust in private homes is from dead skin cells.
Yuck.
So the solution is moisturizer? 
Ergo, stickier dust?
I’m okay with that knowledge, because I’m the only person who lives in my home (and has ever lived there), therefore all the dust is *my *dead skin cells.
I worry more about all the live cells that might be lying around.
There are ten times as many bacterial cells in a human body as there are human cells.
A moving object will build an electrostatic charge. You can buy furnace filters that operate on this principle.
Are there fan filters like that that fit over the blades to negate the collection of dust bunnies?
Actually, yes. You can buy a pack of ceiling fan blade air filters that will (allegedly) help remove the dust from your air. But rather than fitting over the blades, they have a sticky surface and adhere to the top of the blade.
Linky.
If you want your fan blades to collect less dust, try waxing them. Even if they still get dusty, they should be easier to clean. I’d recommend Johnson’s Paste Wax.
Hmm. So that means the fan blades would more evenly distribute the dust to non-moving surfaces that I could just wipe clean?
Does this work on fan blades that aren’t wooden? I have metal and wood fan blades, depending on the room. They all seem to accumulate dust equally.
Waxing the blades will work equally well (or poorly) on metal or wood fan blades. You will also find that the wax, especially the first time, removes a lot of grimy gunk from the blades. Some dust has an oily component that leaves a buildup over time that makes the blades attract dust more readily. A good cleaning with detergent or paste wax removes that oily layer and causes less dust to stick to them for a time. Paste wax has the added advantage of making the blade surface slippery so that dust doesn’t stick as well, making it easier to clean. You will need to re-wax them once or twice a year.
Full disclaimer: I’ve never tried this on ceiling fans, but I do wax my furniture from time to time and it makes dusting much easier.
p.s. - I am not a housekeeper and even if I were, I am not your housekeeper nor am I licensed to keep house in your state. This is not legal housekeeping advice. Please consult a licensed, professional housekeeper in your area before practicing any housekeeping advice given on a messageboard.
Raising my hand for ciggie smoke
Actually, combustion products, from whatever source, including biological metabolism, are wet. That is to say, “sticky.” Moving objects, such as a ceiling fan, will…um…process these remnant particles in greater quantity, AND attract them more due to aforementioned static electricity, AND dry them out as a nasty coating.
If you have a gas stove, you may notice an ugly mess that builds up on the underside of the stovetop. There, heat does the same thing as motion does for the fan (as well as polymerizing the crud into an even worse mess). That may not be as bad if you have one of those newer models that doesn’t use a pilot light.