Recent comments in /f/askscience

SethSky t1_j5egc67 wrote

Reply to Before the Holocene were all humans hunter gatherers? by Kquinn87

The shift towards agriculture and animal husbandry, also known as the Neolithic revolution, allowed for the development of larger, more complex societies and the rise of cities and civilizations. It also led to significant changes in human diet and lifestyle, as people began to rely more heavily on domestic crops and animals for food. But not all of human population made this transition at the same time or in the same way, and some societies continue to rely on hunting and gathering even today. Additionally, it is also worth noting that while the Holocene epoch began around 11,700 years ago, the Neolithic revolution and the transition to agriculture did not happen uniformly around the globe and took place in different time periods and locations.

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Fit_Solution3312 t1_j5e6qeq wrote

Reply to What is the difference between a battery and a capacitor? by Buford12

Capacitors store energy in an electric field, resulting in a linear dependence of stored energy to cell voltage. You can also see this from the capacitor equation for stored energy Emax [Ws] = 0.5 * C [F or As/V] * U^2 [V^2]

Capacitors also do not age by cycling but by holding them at high voltages at high temperatures.

A should can see, capacitors are rated in Farad or Ampere-seconds per volt: it means that a 1 F capacitor will take 1 second at 1 A to charge to 1 V.

Batteries on the other hand depend on a chemical reaction which happens at one specific voltage - as long as there is enough chemicals still available to react, the voltage barely changes.

Batteries are rated in Ampere-hours, as their voltage is stable, meaning that at their given voltage, you can draw 1 Ampere for 1 hour from a battery rated at 1 Ah.

Batteries age by cycling, as the reactions are not 100% reversible.

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Dunbaratu t1_j5e5e0r wrote

Reply to comment by Dorocche in Can planetary rings be a solid surface? by barbadizzy

Even if you had such a fantasy strong material to build it from, a rigid ring doesn't have a stable orbit. Once the tiniest thing knocks it slightly off center, like a single meteor impact, or even the gravity of a passing meteor that doesn't even hit it, the ring would quickly shift further and further off center until one side hits the planet. The orbit isn't self-correcting once you make the object rigid. Quite the opposite - whichever side is closer to the planet gets a stronger pull that pulls it even closer to the planet.

If you wonder why that doesn't happen to individual orbiting satellites, that's because individual orbiting objects that are knocked closer the the planet take on an eccentric elliptical orbit shape which is still stable. But a rigid ring is still stuck in a circle shape even when the "proper" orbit that would remain stable should be an eccentric ellipse.

This raises an interesting question of whether a ringworld that was flexible such that it could be deformed into any ellipse could keep a stable orbit. It still probably couldn't because the same energy orbit that was a circle, when it deforms into an ellipse, ends up being an ellipse with a larger circumference than it had as a circle - so it would have to be both infinitely flexible and infinitely stretchy. That's why a field of rocks and dust can form a stable orbit ring shape (they can form a shape that is infinitely flexible and stretchy since they're not really one joined object.) While a single-object ring really can't.

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Dunbaratu t1_j5e56xa wrote

Reply to Can planetary rings be a solid surface? by barbadizzy

If you work out the math, it turns out a solid circular ring around a gravity well, while it can be in equilibrium, it's not in stable equilibrium. It's in unstable equilibrium. This means once it forms it's not going to be staying that way. The slightest tiniest offcenter effect, including the teeny peterbations from other planets in the solar system, will knock it off center and once that happens the orbit will degrade quickly, until one side of the ring gets closer and closer and hits the parent planet.

In order for the orbit of a ring to be a stable orbit, the material that makes up the ring MUST NOT behave like a single solid rigid object. It has to behave like separate particles each in their own individual orbit. Thus a ring of dust or a ring of rocks works, but something like Larry Niven's Ringworld does not.

(This became a major plot point addressed in the second book in the series, where after being told by fans that the Ringworld as he envisioned it wouldn't stay in orbit, The author invented the notion that the ring was artificially stabilized by having been built with ramjet thrusters along the rim that would constantly turn the solar wind into propulsion thrusting back at the sun. So the closer the ring got to the sun the stronger those thrusters would work, pushing back away from the sun, automatically stabalizing what would otherwise be an unstable system.)

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mtcwby t1_j5e1k3d wrote

Reply to Do other animals have dangerous pregnancies just like humans? by Level_Shift_7516

Cows certainly do. Many years ago I leased my ranch to a local guy who was there before I bought it. There were a couple of things he did that I knew were a bad idea like running some really mediocre bulls with his herd and not controlling the access to the cows. Last straw was I found a way too young pregnant heifer dead in one of the pastures with a breech birth. I called the guy and he was sort of meh about it. I discontinued his lease the next month because he wasn't taking care of his animals like he should. My neighbor above us now leases it for less but is a hell of a lot better cattleman with a lot better cows.

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