Recent comments in /f/askscience

kentMD t1_j2tbbz0 wrote

Reply to Are there any examples of natural hybridization, or any possibilities of this occurring in nature? by Owlsthirdeye

The Amazon Molly is perhaps the most interesting. It exists as an all female species that is a sexual parasite on the two species that it arose from. It uses their sperm to stimulate its eggs but destroys and doesn’t use their genetic material and instead proceeds with a form of parthenogenesis https://en.m.wikipedia.org/wiki/Amazon_molly#:~:text=The%20Amazon%20molly%20(Poecilia%20formosa,essentially%20all%20individuals%20are%20females.

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baggier t1_j2tab8w wrote

Reply to comment by Duros001 in Molecularly, what make pine pitch sticky? by orangegore

I would broadly agree except on the density bit. Tar is not much denser than water but the key attribute is the size of the molecules. Larger molecules have more area to interact with each other, resulting in more attraction and slower motion (e.g. higher viscosity). Tar molecules are about 10-20 times bigger than water.

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KolbeinSterke t1_j2t8hj7 wrote

Reply to comment by Routine_Chain5213 in Are there any examples of natural hybridization, or any possibilities of this occurring in nature? by Owlsthirdeye

Many biologists are now classifying modern humans and Neanderthals as related subspecies. The taxonomical assignations are then Homo sapiens sapiens and Homo sapiens neanderthalensis. There's also evidence of cross breeding with Denisovans, but they haven't been properly classified, yet, and may not be a separate species or subspecies.

The percentage will have been higher among the first tribes to breed with Neanderthals, but probably have fallen to the current level fairly quickly. Generally, "weird" qualities will disappear, unless they're useful (not to mention if they're disadvantageous in their new context), which will reduce genetic variation. This has removed much Neanderthal DNA. Only a few alleles are shared in modern populations.

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die_kuestenwache t1_j2t0rp6 wrote

Reply to comment by SW_Zwom in If an object is placed at the end of of a VERY long bar that is connected to an axel, Could rotating the bar close to the axel make the object at the other move extremely fast (like light speed)? by Swade060504

In principle, yes. Infinite rigidity would mean infinite speed of sound. As soon as the velocity of any part of the rod approaches the speed of light, the torque necessry to further accelerate the rod would go towards infinity. However, as others have pointed out, infinite rigidity violates relativity as the speed of sound itself cannot exceed the speed of light.

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solenyaPDX t1_j2t00wt wrote

Reply to comment by Weed_O_Whirler in If an object is placed at the end of of a VERY long bar that is connected to an axel, Could rotating the bar close to the axel make the object at the other move extremely fast (like light speed)? by Swade060504

Even if we assume a non flexing support rod, you'd need to apply torque to the axle to move the object. The energy required to move the object wouldn't change, so you'd be looking at infinite torque necessary to turn the axle.

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OverJohn t1_j2swp18 wrote

Reply to If an object is placed at the end of of a VERY long bar that is connected to an axel, Could rotating the bar close to the axel make the object at the other move extremely fast (like light speed)? by Swade060504

Rigidity and relativity is more complicated than you might think.

Firstly, relativity constrains the speed of sound in an object. This means for example you cannot have a rigid pole where pushing one end causes the other end to move instantaneously.

Secondly, relativity constrains rigidity even further. We could conspire to apply forces across an object at the same time in its instantaneous rest frame such that the object never experiences deformation in its rest frame. When we do this the object is called "Born rigid" (after Max Born). However it turns out it is impossible to for an object to be Born rigid under all types of motion. The motion in your son's hypothetical experiment would be an example of a type of motion where it is impossible to even maintain Born rigidity.

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[deleted] t1_j2swk1z wrote

Reply to comment by JonJackjon in How do galaxies move? by modsarebrainstems

>now is not quite everything but currently expanding size.

Well, the space between stuff is what is expanding/being created constantly,the galaxies are stationary (kinda, not really.)

>Seriously, could we go to the edge of the universe then stick a meter stick a little bit further.

No.

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Pink_Axolotl151 t1_j2svyz2 wrote

Reply to comment by derioderio in How are birth control failure rates even calculated? by [deleted]

I’m an immunologist; we don’t do math.

Kidding, kidding, I understand, but I don’t think it’s intuitive to most people that it works like that. A lot of people think that the quoted failure rates (ie, 2% for male condoms) are the failure rates over a lifetime of use, and the graphics in the article help hammer the message home.

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