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Re: Miscellaneous Science Questions

Posted: Fri Sep 15, 2017 3:53 am UTC
by Eebster the Great
Also make sure you always hit the same part of the mug. The pitch will vary with the position relative to the handle.

Re: Miscellaneous Science Questions

Posted: Fri Sep 15, 2017 5:34 pm UTC
by Sizik
Eebster the Great wrote:Also make sure you always hit the same part of the mug. The pitch will vary with the position relative to the handle.

As demonstrated here

Re: Miscellaneous Science Questions

Posted: Sun Sep 17, 2017 12:31 am UTC
by Heimhenge
commodorejohn wrote:Okay, explain this to me, all you lay physicists (or, um, even any professional physicists, you're cool too):

  1. Make a nice steaming mug of hot cocoa. Use a reasonably sturdy mug.
  2. Put a spoon in the glass and begin steadily tapping at the bottom. The sound of the tapping will rise in pitch.
  3. Do it less steadily. The pitch will not cease to rise. There will be no noticeable correlation between the rate or regularity of the tapping and the rate of change in pitch.
  4. Walk away and leave the entire thing alone for a few minutes.
  5. Come back and start tapping again. IT WILL CONTINUE AT THE SAME PITCH IT LEFT OFF AT.
Why is this? If the pitch rises due to, say, energy imparted to the glass or the beverage, it should decay over time, which would mean that a slower rate of tapping would result in a smaller rate of change in pitch, and walking away for a few minutes should cause the pitch to drop noticeably. If it's some kind of resonance in the chamber, it should simply emphasize frequencies close to the resonant frequency of the glass and de-emphasize others. The heck's going on here?


That seems like it'd have to be a subjective effect. The resonant frequency should only depend on the size/shape of the resonator, and the speed of sound in the liquid. Don't see how tapping rate could have an effect.

I've noticed something similar for ages but never got around to actually investigating the effect. When I stir my instant coffee into a cup of microwaved hot water, the clinking of the spoon against the porcelain mug starts at a higher frequency and drops to a lower frequency as I stir. Not much ... maybe a half-note. I always attributed it to the expansion of the mug as it absorbed heat which would lower the resonant frequency. But I still wonder if maybe it might have something to do with the coffee dissolving and changing the density of the liquid?

Re: Miscellaneous Science Questions

Posted: Sun Sep 17, 2017 12:34 am UTC
by commodorejohn
Hmm, that's an interesting comparison. But what I'm noticing (if, again, it's not purely perceptual/brain weirdness) is on the order of a good octave or more total change over time.

Re: Miscellaneous Science Questions

Posted: Sun Sep 17, 2017 12:56 am UTC
by Eebster the Great
It does seem like this would be pretty easy to resolve with a cup of hot chocolate, a spoon, and a microphone.

Re: Miscellaneous Science Questions

Posted: Sun Sep 17, 2017 2:39 am UTC
by commodorejohn
It does. A guy should probably get around to that at some point.

Re: Miscellaneous Science Questions

Posted: Thu Sep 21, 2017 5:18 pm UTC
by SuicideJunkie
Eebster the Great wrote:It does seem like this would be pretty easy to resolve with a cup of hot chocolate, a spoon, and a microphone.

It would probably be worth adding a metronome to consistently tap the spoon as well.

Re: Miscellaneous Science Questions

Posted: Thu Nov 02, 2017 4:22 pm UTC
by p1t1o
I've noticed this.
I thought it was fairly obvious that as the teaspoon cools, its resonant frequency changes due to minute changes in size and flexibility as it contracts.
A shorter, stiffer spoon rings at a higher frequency.
I presume the effect described in point #5 is subjective and would be eliminated on examination.

Re: Miscellaneous Science Questions

Posted: Thu Nov 16, 2017 2:33 pm UTC
by jewish_scientist
Yesterday a student in my environmental anthropology class claimed that global climate change can cause volcanoes to erupt more frequently. When I asked for an explanation, they just muttered something about tectonic plates under the ocean and CO2. There is no way that this can be correct. The mass of the Earth's mantle and crust is several magnitudes greater than that of the atmosphere, so how can anything involving the atmosphere be non-trivial?

Re: Miscellaneous Science Questions

Posted: Thu Nov 16, 2017 4:05 pm UTC
by gmalivuk
I don't think it would affect suboceanic plates or be a direct consequence of CO2 concentrations, but the existence of a connection isn't totally far-fetched.

If some type of tectonic activity is already near a tipping point, then even small changes in pressure (such as air pressure in a storm) or mass distribution (such as from rain, flooding, and resulting mudslides) could potentially trigger something.

No one's arguing that climate change impacts the overall direction of plate tectonics, but individual events don't depend on anything as large as the entire crust or mantle.

Re: Miscellaneous Science Questions

Posted: Thu Nov 16, 2017 4:19 pm UTC
by p1t1o
There have been seismic events linked to things like dams filling (and the 3 gorges dam in china measurably affected the rate of Earth's rotation), so its not super crazy, especially if the sea level rises land-based ice melts significantly. Its not about excess weight, its about it being re-distributed. Its not going to cause a 2012[movie]-like shift of the continents or anything stupid though, and I highly doubt it is going to have global effects like "volcanoes will erupt more frequently".

https://en.wikipedia.org/wiki/Induced_seismicity

Re: Miscellaneous Science Questions

Posted: Thu Nov 16, 2017 11:34 pm UTC
by Eebster the Great
If this is just tipping things like quakes and eruptions over the edge, wouldn't they happen eventually anyway? I'm not sure I understand how they could make them more frequent in the long run.

Re: Miscellaneous Science Questions

Posted: Fri Nov 17, 2017 12:52 am UTC
by eSOANEM
unrelated to the above, just a random fleeting thought:

if we started selectively breeding ballerinae, roughly how many generations would it take before they become ungulates (due to the selective pressure of dancing en pointe)?

Re: Miscellaneous Science Questions

Posted: Fri Nov 17, 2017 2:05 am UTC
by Liri
eSOANEM wrote:unrelated to the above, just a random fleeting thought:

if we started selectively breeding ballerinae, roughly how many generations would it take before they become ungulates (due to the selective pressure of dancing en pointe)?

Don't forget to work in the diet of course grasses.

Within 100 generations is "rapid evolution", so we're probably looking at at least that, even with the artificial selection. Only a couple millennia to achieve perfection.

Re: Miscellaneous Science Questions

Posted: Mon Nov 27, 2017 3:45 pm UTC
by jewish_scientist
If a species reproduces asexually, then what gender are members of that species?

Re: Miscellaneous Science Questions

Posted: Mon Nov 27, 2017 3:52 pm UTC
by Zohar
Gender is a concept that relates to the culture of a species, not reproduction. Sex is probably what you're looking for here. Why would there be different sexes in these species at all?

Re: Miscellaneous Science Questions

Posted: Mon Nov 27, 2017 4:34 pm UTC
by gmalivuk
For larger animals (such as reptiles that reproduce through parthogenesis) scientists generally refer to all of them as females, because they lay eggs or give birth.

Re: Miscellaneous Science Questions

Posted: Mon Nov 27, 2017 4:42 pm UTC
by doogly
jewish_scientist wrote:If a species reproduces asexually, then what gender are members of that species?

It's polite to just ask them.

Re: Miscellaneous Science Questions

Posted: Mon Nov 27, 2017 8:11 pm UTC
by Eebster the Great
There are also species that can reproduce both asexually or sexually (this is especially common in plants). In some cases, all members of those species are hermaphrodites. In other cases, some but not all members could be hermaphroditic, or none could be. Some plants and animals even undergo sex-switching.

Re: Miscellaneous Science Questions

Posted: Thu Nov 30, 2017 11:59 pm UTC
by jewish_scientist
There are actually some snakes that can reproduce sexually and asexually even though they are not hermaphrodites. In the case of asexual reproduction, the female lays an egg containing a clone.

Re: Miscellaneous Science Questions

Posted: Fri Dec 01, 2017 4:47 pm UTC
by Zohar
jewish_scientist wrote:There are actually some snakes that can reproduce sexually and asexually even though they are not hermaphrodites. In the case of asexual reproduction, the female lays an egg containing a clone.

If you already know the answer to your own question, may I ask why you posed it in the first place?

Re: Miscellaneous Science Questions

Posted: Sun Dec 10, 2017 3:38 am UTC
by Liri
I had been meaning to ask for a while whether there was a theoretical "maximum temperature" and decided to look it up before asking here. Lo and behold, there is! And it's actually pretty interesting.

Re: Miscellaneous Science Questions

Posted: Sun Dec 24, 2017 5:43 pm UTC
by jewish_scientist
You should look into negative temperatures, which are all actually hotter than positive temperatures.

Re: Miscellaneous Science Questions

Posted: Sat Dec 30, 2017 12:38 am UTC
by eSOANEM
This is a lot less weird when you realise that Thermodynamics is generally a lot nicer when you formulate it in terms of β=1/(kBT) (this does result in heat flowing from low β to high which is clearly wrong so instead of the usual normalisation scheme of setting kB=1 we ought to go for kB=-1 although I am aware that this is an unpopular opinion)

Re: Miscellaneous Science Questions

Posted: Tue Jul 31, 2018 4:21 pm UTC
by RyvenZ
New guy hoping to glean wisdom from other XKCD fans; I have a question I am unable to find the answer for.

Napoleon Dynamite's Uncle Rico character wagers he could "throw a football over them mountains" and I wanted some help building a formula that I can use to figure out how impossible it would be to do such a feat. I took physics a long time ago and had forgotten most of the physical world stuff and we never did go over air resistance, which cannot be ignored if this is to be answered correctly.

Is this something that we can simply get to a formula requiring only angle and release velocity?

Knowns:
* An NFL football weighs 14-16 oz. Most physics seems to be in metric, so let's say 450 g as a near middle estimate
* The density of air is 1.2 kg/m3.
* The coefficient of drag for the football is 0.05 to 0.14

I've tried asking this on reddit a while back, and it got no traction so was never answered.

Thanks in advance!

Re: Miscellaneous Science Questions

Posted: Wed Aug 01, 2018 4:47 am UTC
by Eebster the Great
The most important parameters are the distance to them mountains and the height of them mountains. The others have only minor significance. You also can't really do anything with just density of air and coefficient of drag, but at the end of the day, drag isn't worth worrying about anyway, because you can't throw a football nearly that far in a vacuum anyway.

Re: Miscellaneous Science Questions

Posted: Wed Aug 01, 2018 5:53 pm UTC
by DavidSh
Eebster the Great wrote:... because you can't throw a football nearly that far in a vacuum anyway.

That depends on another parameter, the acceleration of gravity. On a suitably sized asteroid, you might be able to throw a football that far. If your suit is sufficiently flexible.

Re: Miscellaneous Science Questions

Posted: Wed Aug 01, 2018 5:56 pm UTC
by Xanthir
But a football cannon *could* launch it that far in a vacuum, theoretically. (Well, assuming that the football can stand up to the acceleration of the cannon. But imagine an arbitrarily-long football-railgun that can bring it to the desired velocity at an appropriately low acceleration.)

But when you do take drag into account, you'll find that there is absolutely no way to do it; footballs are fairly low mass, and while they slide air around themselves pretty reasonably at the speed/distances that normal throwing takes place, the speed you'd need to hit to counteract drag over the distance of a mountain-transit would absolutely destroy the football upon contact with said air.

Re: Miscellaneous Science Questions

Posted: Thu Aug 02, 2018 1:32 am UTC
by Eebster the Great
Fair enough. The circumference at the equator of an NFL football is about 22 inches apparently, so if we model it as a right circular cone, its cross-sectional area is about 250 cm2. I'll accept the drag coefficient values, and I'll give Uncle Rico the benefit of the doubt and assume he has a perfect spiral, so 0.05. The force of drag is F = ½ρACdv2, where ρ=1.3 kg/m3 is the density of air, A=250 cm2=0.025 m2 is the cross-sectional area of the football, Cd=0.05, and v is the speed of the football. That simplifies to F = (0.00081 Kg/m) v2, or if the football's mass is 420 g, an acceleration of a = (0.0020 m-1) v2.

The problem is still that we don't know how far away or tall them mountains are, so we can't solve for v. Let's say v=1 km/s. Then a=2 km/s2, or 200 g. But I don't know if that's a reasonable v.

Re: Miscellaneous Science Questions

Posted: Thu Aug 02, 2018 1:41 pm UTC
by Copper Bezel
Heimhenge wrote:I've noticed something similar for ages but never got around to actually investigating the effect. When I stir my instant coffee into a cup of microwaved hot water, the clinking of the spoon against the porcelain mug starts at a higher frequency and drops to a lower frequency as I stir. Not much ... maybe a half-note. I always attributed it to the expansion of the mug as it absorbed heat which would lower the resonant frequency. But I still wonder if maybe it might have something to do with the coffee dissolving and changing the density of the liquid?

I know this is an old post, but they're describing the hot chocolate effect, right?

Re: Miscellaneous Science Questions

Posted: Thu Aug 02, 2018 4:22 pm UTC
by gmalivuk
Eebster the Great wrote:Fair enough. The circumference at the equator of an NFL football is about 22 inches apparently, so if we model it as a right circular cone, its cross-sectional area is about 250 cm2. I'll accept the drag coefficient values, and I'll give Uncle Rico the benefit of the doubt and assume he has a perfect spiral, so 0.05. The force of drag is F = ½ρACdv2, where ρ=1.3 kg/m3 is the density of air, A=250 cm2=0.025 m2 is the cross-sectional area of the football, Cd=0.05, and v is the speed of the football. That simplifies to F = (0.00081 Kg/m) v2, or if the football's mass is 420 g, an acceleration of a = (0.0020 m-1) v2.

The problem is still that we don't know how far away or tall them mountains are, so we can't solve for v. Let's say v=1 km/s. Then a=2 km/s2, or 200 g. But I don't know if that's a reasonable v.

You can figure out how high and far that v would get you and then decide whether it's reasonable.

For example, while we don't know the exact distance or height, we can at least guess that "them mountains" are far enough away that Rico isn't already at the base of them (else they'd be "these mountains" or "this mountain"). We can also guess that they're at least on the order of 1km high, else they'd hardly warrant being called mountains.

So, can 1000m/s get you a kilometer up at a horizontal distance of more than 1km?

Re: Miscellaneous Science Questions

Posted: Fri Dec 28, 2018 10:41 am UTC
by tomandlu
The universe cannot be infinitely old, since if it was, it could never have reached the present moment - true or false?

Re: Miscellaneous Science Questions

Posted: Fri Dec 28, 2018 1:24 pm UTC
by doogly
tomandlu wrote:The universe cannot be infinitely old, since if it was, it could never have reached the present moment - true or false?

Extremely false. This is like classic Zeno level nonsense.

Re: Miscellaneous Science Questions

Posted: Fri Dec 28, 2018 2:11 pm UTC
by tomandlu
doogly wrote:
tomandlu wrote:The universe cannot be infinitely old, since if it was, it could never have reached the present moment - true or false?

Extremely false. This is like classic Zeno level nonsense.


Aren't (most/all?) of Zeno's Paradoxes about creating infinities out of finite things? This seems to be the opposite IYSWIM...

Re: Miscellaneous Science Questions

Posted: Fri Dec 28, 2018 4:19 pm UTC
by gmalivuk
There are an infinite number of points between 0 and 1, and yet Zeno's arguments are still flawed.

Re: Miscellaneous Science Questions

Posted: Fri Dec 28, 2018 4:32 pm UTC
by tomandlu
gmalivuk wrote:There are an infinite number of points between 0 and 1, and yet Zeno's arguments are still flawed.


There are also an infinite number of points between zero and infinity. If the tortoise started with a 1% lead, the hare would never have caught it... What I'm saying is that, yes, it's silly to split a finite thing into infinities and then declare that the finite thing is infinite (which most of ZPs seem to do). However, I'm wary of making assumptions about true infinities based on that (such as a universe of infinite duration).

Re: Miscellaneous Science Questions

Posted: Fri Dec 28, 2018 5:02 pm UTC
by doogly
What you are proposing is that because there is an infinite extent in one direction, there cannot exist points at some finite distance from the origin. This makes no sense.

Or perhaps what you are observing is that if you have something with an infinite extent, say a real line or an entire universe, whatever, you can't put your origin of coordinates at the "beginning" or "all the way to the left." It is true. You cannot do that. You cannot mark time from the beginning of the universe if the universe is infinite, but that doesn't mean the universe can't be infinite.

Re: Miscellaneous Science Questions

Posted: Fri Dec 28, 2018 5:11 pm UTC
by Quizatzhaderac
So a "Hypercarnivore" is any species of animal whose natural diet is 70% or more meat. In order for this not to be a stupid name/categorization, I'd expect two things to be true: 1) this category is especially carnivorous 2) A large proportion of members of this category are in the 70-99% range.

These two assumptions would imply that a lot of the animals I think of as "Carnivores" have diets containing non-animal matter. So what specifically do these animals eat apart from meat? So it would depend on the animal, so using Wikipedia' examples of hypercarnivores, what do alligators, eagles, lions, wolf, dolphins, snakes, spiders, scorpions, and sharks eat aside from meat?

Re: Miscellaneous Science Questions

Posted: Fri Dec 28, 2018 5:16 pm UTC
by tomandlu
doogly wrote:What you are proposing is that because there is an infinite extent in one direction, there cannot exist points at some finite distance from the origin. This makes no sense.


I was more thinking of infinite in both directions - it started an infinite amount of time ago being the significant point.

Re: Miscellaneous Science Questions

Posted: Fri Dec 28, 2018 6:10 pm UTC
by Quizatzhaderac
tomandlu wrote:The universe cannot be infinitely old, since if it was, it could never have reached the present moment - true or false?

I really don't see how B follows from A, and people taking guesses seem to be thinking very differently from you.