I sweat pretty much everywhere fairly profusely but my hands just don't get super sweaty.

A lens takes all the light rays coming from a certain direction and bends them so they all end up in the same place. In the case of your eye, they need to end up on the retina. When your pupil is larger, you have to bend the rays coming in at the edge more than the rays going through the center of your pupil. Terrible vision (usually) happens because the lens of your eye isn't bending the light rays by the right amount. Let's say your lens only bends them half as much as it should. Light going through the center of your pupil isn't affected because it they go straight through. Rays near the center get bent by the wrong amount, but because they weren't getting bent very much still end up in nearly where they should have. But rays that come through the edge of your pupil need to get bent by a lot, so when your lens isn't working right, they end up a long ways from where they should. That makes your vision fuzzy, because the light from say a single light bulb ends up spread all over your retina. If you block the outer parts of your pupil, though, those rays that ended up a longs ways off and made your vision fuzzy get blocked, so the light that does make it through ends up where it is supposed to.

The limiting case of this is, as people have mentioned, a pinhole camera. The pinhole doesn't bend the light at all, so what you end up with is a picture that has been smeared out by the size of the pinhole. The smaller the pinhole, the sharper (and fainter) the image. The eye is better than a pinhole because it's at least trying to focus, but it is the same basic idea.

Note that air resistance is only proportional to the square of the speed, so the heading of the linked article is incorrect. Resistance is a force. It's power that goes with the cube, because it's proportional to force multiplied by speed.

I think this explanation was the best explanation imo, you indeed explained it like I’m 5. Take my upvote!

There was a fairly recent study on the impact of nuclear weapons on the ozone layer. It turns out it only takes a remarkably small number of nuclear detonations to do serious damage to the ozone layer.

So strictly from an explosive force impact nuclear weapons would not be able to destroy everything on the planet, but fire a few here and there across the world and you wouldn't need to. The UV radiation from the sun would effectively wind up sterilizing the surface of the planet.

It is also, incidentally, pretty bad for the soil to drive fast on top of it -- going faster than 5 mph increases "washboarding" (or "corrugation"). Tires (and the weight of the vehicles on top of them) are TERRIBLE for soil, and a huuuuuuuge amount of research is put into ensuring that tractor tires compact the soil as little as possible. And even with those beautiful soil-protecting tires, if you're going faster than 5 mph, you're damaging the soil no matter what. Even if your tractor COULD go fast, you don't WANT it to.

From the end of the Civil War through World War 2, poor white Southerners suffered almost as badly as black Southerners. Most suffered silently, but some became violent, and blacks were convenient and vulnerable targets.

Because blacks were not allowed to vote, and juries were selected from registered voters, all jurors were white. And no white jury would convict a white man of violent crimes against blacks.

So if you wanted to commit violence, you could do so against blacks without consequences. Maybe violent poor whites were really mad — or just as mad — at rich whites. But rich whites were protected by the law.

This violence served the rich whites, because it gave the anger of poor whites a different target while terrorizing poor blacks. So they did little to discourage it, and often encouraged it.

I have heard that they were afraid they themselves would be made slaves. Also a lot of rich southerners lost all their free labor and if you get between somebody and their money they will do and say terrible things to keep it

Well, they probably didn't is the answer.

The problem is fear and distrust. A significant part of the economy functioned through the use of slaves. If you are used to treating something as property and that thing is essential for your wellbeing, it is hard to now rethink this attitude.

In any society, the idea of comparison and threats are the worst in the poorer parts of the community. It is easy to think of every situation as a win-lose proposition - someone else's gain is your loss and vice versa. If you're starving, having someone else compete with you for food can generate existential fear.

The appeal of a perpetual motion machine is free energy. If a perpetual motion machine was possible, you could harvest energy from it and it would never stop, and you’d have an endless supply of energy.

Since perpetual motion machines are not possible to make, there’s no point in trying to build something as close as possible to a perpetual motion machine because it will always slow down faster than the rate at which you pull energy out of the system.

The only modern practical application of that idea would be in a flywheel battery where you make a machine spin really fast and then try and keep it spinning with as little energy loss as possible before you extract stored energy out of the device.

We usually balance our creations between efficiency, effectiveness, and aesthetics. As you make something more efficient, that will eventually come by sacrificing effectiveness.

It boils down to that is what the rich and those in power told them to. Before the Civil War African-americans were depicted as sub human. After the rich told poor people that the "lazy blacks were coming for the land and jobs." And that rhetoric still exists today.

As plowing speed increases, draft also goes up, but usually varies as the square of ground speed. In practical terms this means that by doubling the ground speed, say from two to four miles per hour, the draft increases four times.

Bombs dropped on Japan were in the 10-20 kiloton range. Very Big cold war era H-bombs were up.to about 20 megatons, so about 1000 X. Contemporary missile carried MIRV bombs run around 150 kilotons, about 10 X. Militarily speaking, more, smaller bombs are more useful.than a few big bombs.

In about 1975 I saw an estimate that about 400 medium size bombs would be required to completely destroy everything and everyone in the Soviet Union. (This estimate only considered "prompt" deaths and destruction. No consideration was given to long-term radioactive damage or starvation. Yes, it was a fun time to grow up, why do you ask?)

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Or, more simply put: the world is very, very big.

There is something called the inverse square law. Basically, at least for rhe radiation and the energy, double the distance = one quarter the dose. So the effects even a very large explosion disipate very quickly with distance.

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We tend to underestimate the size of the world and overestimate (due to fear etc) the capability of humans.

The atomic bombs dropped on Japan were powerful FOR THEIR TIME. But it didn't even destroy a single (not very large) city. It certainly did not kill the entire population of that city, not even close. The immediate blast radius was something in the region of a few miles.

Even a bomb a thousand times more powerful (today) would not be capable of destroying a large city. Things work exponentially so we could perhaps get a blast radius of ten miles (depending on how it was exploded) with some of the larger hydrogen bombs of today.

The earth has a circumference of 25,000 miles (give or take). As a point of reference, a major volcanic eruption or earthquake releases far more energy than even our largest bombs.

These weapons are massively destructive but are no where close to where a few of them could wipe out a small region.

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Horsepower is derrived from a mathematical function where torque is multiplied by RPM and divided by some constant. It's why a Harley Davidson can make a ton of torque down low, but have much lower HP numbers than you would expect - they just don't rev very high. A tractor is going to be similar. You want a boat load of low down torque off idle so you can plough through dirt and mud, but you don't need it to go very fast, so there's no point in making it rev as high as a car. If those engines could spin as fast as car engines, they'd make substantially more power, but they don't spin very fast, so the HP number is low

This would fit the description as well.

Thanks.

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