Recent comments in /f/askscience

bella_68 t1_j5s8tpz wrote

Reply to comment by Lampshader in Why does hot air cool? by AspGuy25

Idk how hot a car gets when sitting in the sun but it was hot enough to melt the glue on the electrical tape covering my steering wheel. Interestingly, the glue was liquid and the liquid was everywhere but the tape was still on the steering wheel because the way it was wrapped and the fact that the glue was also still there to some extent.

Unfortunately for me, I get a rash anytime I touch glue

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AStrangerSaysHi t1_j5s2n5u wrote

I don't know why reading this answer triggered a childhood memory for me, but: as a kid, I used to love loess... rocks? stones? collections? deposits? clumps?... and would collect bits of it whenever we visited eastern Georgia on vacations (I'm from the dueling banjos part of Georgia for reference). I remember loving the texture of those little bits.

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zebediah49 t1_j5s0zx3 wrote

Reply to comment by Denamic in Why does hot air cool? by AspGuy25

The relevant point is that visible light will happily go through a normal glass window, whereas long-IR will not. Windows are opaque (and pretty reflective) to thermal cameras.

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Lampshader t1_j5rzle5 wrote

Reply to comment by dr_reverend in Why does hot air cool? by AspGuy25

The FLIR sales rep recommended black electrical tape when I asked about this.

I dunno what its melting point is but 98% of electronics workbenches will have it within arm's reach already so it's got that going for it

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thereisafrx t1_j5rz7fz wrote

Think about it this way, if you put a quarter on a small hill and rolled it down the hill, and a large stone disk on a proportionally-larger hill, would the large stone disk roll for longer?

Same for the two cases of the fluids in large/small containers, except with the solids there are no viscous forces to consider.

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junegoesaround5689 t1_j5rypyu wrote

Evolution doesn’t (and can’t) "retrace its steps". So, almost certainly this would be impossible. It would be like two different rainstorms producing exactly the same raindrops falling in exactly the same places with identical lightening and thunderclaps. Waaaay too many variables for the exact thing to happen twice. Similar (ref convergent evolution), yeah, but not identical.

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PineappleLemur t1_j5rx08g wrote

Thermal cameras see IR, metals, especially bare metals have a really low emissivity, meaning that they radiate very little IR and reflect the rest. (what the camera sees)

Think of it as a mirror, aluminum foil for example has emissivity of under 0.1 (it's a scale of 0-1, 1 being 100% radiating/absorbing) so only 10% of the total possible energy is being radiated and 90% are being reflected.

What you're seeing is a combination of the reflected IR + the radiated IR.

So the surface reflected is likely what you're seeing + the housing.

Take an aluminum foil and literal look at yourself with the camera. Foil is basically a mirror for IR as a glass mirror is for white light (what we see)

Emissivity is affected by material/color/surface. To get a better reading you want to paint it with a black body color, something black with a rough surface and very little visible shine (matte black)

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VulfSki t1_j5rqk0a wrote

Reply to comment by Glasnerven in Why does hot air cool? by AspGuy25

Yes, I understand how all that functions. Humans get cooked down from perspiration, which is because the energy to evaporate sweat is partially comes form the heat on our body, and air flow helps with that.

But airflow itself doesn't equal cooking in the general sense, because it only works if you are removing heat by taking it to something that is at a lower temperature, can't violate newton's law of cooling.

You did provide a great explanation, even though I was already aware of all that.

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