**Ask a monkey a physics question thread**

[MadMojoMonkey]

@ong: No. Skin is not rich in either magnesium or calcium. That's what fertilizer is for.

@poop: I concede that neither of us is definitively correct on the question of "what is dust?"

A) There are a ton of conflicting sources, and even the quotes I can find by "experts" on dust lack any links to their studies and data.

B) Dust is a definition of particulate size. Any object or substance which is of that physical size is considered dust.
Therefore, the composition of dust varies widely from location to location.
(Dust at a smelter is going to be dramatically different than dust in a house.)

C) Dust from textiles and hair tends to be fluffy, or lower density than skin dust. Dust from human skin cells and the dust mites that eat them tend to be compact, and have a higher density.
The ratio of what is most prevalent will be different if you're comparing amounts by volume or amounts by mass.
The sources I've found do not state which metric they've used to draw their conclusions.

[Poopadoop]

@poop: I concede that neither of us is definitively correct on the question of "what is dust?"

Don't concede anything on my behalf lol.

A) There are a ton of conflicting sources, and even the quotes I can find by "experts" on dust lack any links to their studies and data.

B) Dust is a definition of particulate size. Any object or substance which is of that physical size is considered dust.
Therefore, the composition of dust varies widely from location to location.
(Dust at a smelter is going to be dramatically different than dust in a house.)

C) Dust from textiles and hair tends to be fluffy, or lower density than skin dust. Dust from human skin cells and the dust mites that eat them tend to be compact, and have a higher density.
The ratio of what is most prevalent will be different if you're comparing amounts by volume or amounts by mass.
The sources I've found do not state which metric they've used to draw their conclusions.

One thing that seems clear is that there isn't sufficient volume or mass of shed skin cells to make up the majority of house dust. An empty house collects dust, for example, though there's obviously no human skin cells being shed in it. I'm inclined to think house dust is mostly mineral matter (i.e., dirt) and plant matter (e.g., pollen), with animal matter coming in a distant third behind those two.

[MadMojoMonkey]

Don't concede anything on my behalf lol.

That's fair.
I didn't mean to.

Oops.

One thing that seems clear is that there isn't sufficient volume or mass of shed skin cells to make up the majority of house dust.

Upon what data is this assertion based? I looked for any data to affirm or refute this claim and I found none.

An empty house collects dust, for example, though there's obviously no human skin cells being shed in it.

This is already addressed by my point (B) above.

I'm inclined to think house dust is mostly mineral matter (i.e., dirt) and plant matter (e.g., pollen), with animal matter coming in a distant third behind those two.

If you're not willing or able to present data on this, then you're welcome to start the "Things Poopadoop is inclined to think, despite the dearth of evidence" thread.

[Poopadoop]

If you're not willing or able to present data on this, then you're welcome to start the "Things Poopadoop is inclined to think, despite the dearth of evidence" thread.

How about "Things that appear to be common sense" thread?

Your outer layer of skin regenerates once every 35 days. Take that amount of dead skin cells, multiply it by the number of people in the house, subtract a big chunk for the skin that gets sloughed off while people are outside the house and/or washed down the shower/sink drain, then divide that by the surface area of everything in the house, including carpets, tables, etc.. How thick a layer of dust do you think that would make?

Maybe you should start a "Things you heard somewhere and thought sounded cool so you repeated them as though they were facts, and then got argumentative when someone pointed out they were bullshit" thread.

[MadMojoMonkey]

How about "Things that appear to be common sense" thread?

That'd be fine, too.

Your outer layer of skin regenerates once every 35 days. Take that amount of dead skin cells, multiply it by the number of people in the house, subtract a big chunk for the skin that gets sloughed off while people are outside the house and/or washed down the shower/sink drain, then divide that by the surface area of everything in the house, including carpets, tables, etc.. How thick a layer of dust do you think that would make?

I'm not saying you're wrong. I'm saying I can't find any data which backs up your claim.
I'm saying if you can't or don't want to find any data which supports your position, either, then this is the wrong thread.

Maybe you should start a "Things you heard somewhere and thought sounded cool so you repeated them as though they were facts, and then got argumentative when someone pointed out they were bullshit" thread.

I didn't say it because it sounds cool. I said it because my best friend for 30 years wrote a paper on dust (admittedly, in high school), and he told me the thing about skin cells. It seemed like a reliable enough source at the time. It wasn't until you questioned it that I ever heard contrary.

I took your position to heart and embraced skepticism about my own position. I looked for relevant data or evidence to elucidate the situation. I found inconclusive statements from "experts" and contradictory statements between different articles.

I'm not arguing with you. I'm saying I can't find evidence to definitively support either of our positions.
If anything, I'm disagreeing with your position as definitive, and I've stated 3 reasons for my skepticism.

[Poopadoop]

I don't need scientific data to tell me when things clearly don't add up - that's why i have common sense. And common sense tells me I'm a lot smaller than my house and there's no way I could shed enough skin to create a visible layer of dust over the entire house every few days.

But if you're still not convinced, then let's do the maths.

A layer of skin varies from 0.5 to 1.5 mm thick, depending on where on the body you measure it. The average person has 1.5-2.0 m surface area of skin. The average house has maybe 100 m2 of floor space.

0.001 m layer of skin * 1.75 m2 surface area of skin on the body = 0.00175 m2 of skin cells shed every 35 days by the average person. Assuming 3 people live in the house and never leave the house or wash themselves that makes 3* 0.0175 = 0.00525 m2 of skin cells.

Now spread that out over 100 m2 of floor space- we'll just ignore the furniture and whatnot for the sake or argument. That's a layer of skin 0.0525 mm thick that would accumulate over 35 days, not enough to even see with the naked eye. I see dust visibly accumulating in my house a few days after dusting. It also accumulates when I'm away from the house for a few days.

Ergo, the skin cells theory of dust is as retarded as it sounds.