How does a computer unset a bit (set it from 1 to 0) in memory/storage?

It depends on the particular kind of storage.

In magnetic storage, like a spinning-disk hard drive, it magnetizes the region storing the bit in the opposite direction.  (In practice, hard drives write entire blocks at a time, but the technology could theoretically be managed a bit at a time.)

In typical flash storage, like in solid-state drives or external flash drives, it can't write a single bit at a time. In order to change a bit from a 1 to a 0, it erases an entire block of memory, then rewrites the new data into it.

In DRAM, which is the typical kind of RAM in a computer, it connects the capacitor holding the bit to a current drain, which allows it to discharge.  (Similarly to others, standard DRAM actually can only write a whole line at a time, so switching a single bit means writing the previous value into all the other bits.)

In SRAM, which is typically used for things like on-CPU caches, the bit line is set to 0 and then the write line is set to 1.  The transistors switch into the alternative configuration, and then the write line is set back to 0, which causes them to maintain their current configuration until written again.

How do motion detectors detect motion in the dark?

There are two common types of motion sensors - passive infrared (PIR) and Ultrasonic. The most common type is PIR which sees IR which is emitted by hot objects. There is a special lens in front of the sensor so a warm object moving through its field of view creates sudden transitions that are easy to detect. Since it is relying on heat emissions it works fine with or without light.

Ultrasonics send out a sonar burst and effectively echo locate like a bat. They check the sound they get back after each one and compare it to the last one, if it changed significantly then something in the space moved and they trigger.

How can a piece of paper folded 103 times be larger than the observable universe?

Exponential growth. Each fold doubles the thickness of the paper. If someone gave you 1 penny today, and promised to give you twice as much money tomorrow, and twice as much the day after, and so on and so on, on day 30 they would have given you over $5 million.

You can do the math on this. Open the calculator on your computer, and type in 0.0039 (the thickness of a piece of paper).  Press the Times button, and then the number 2, and press enter. Now press enter 102 more times. By the mid-50's your calculator will actually reach a point where it has to start using exponents, and by 60 you'll have surpassed the what the calculator is capable of.

How is it possible for ISP's to know we are doing online? Isn't HTTPS supposed encrypt content so it can't be read?

The ISP (Internet Service Provider) is your mailman. They need to get packages to where they need to go. HereBeAnswers, for example, is sending you a package containing this answer. You pay the mailman monthly for a rate at which they send packages from you and to you.

HTTPS encrypts the package's contents, however the ISP's responsibility is still to move the package from A to B, and therefore needs to know what these A and B are. Therefore the postage address cannot be encrypted, and your ISP can track who you are exchanging packages with, be it HBA or YouTube or Netflix.

So your ISP can't actually see what you are viewing on HBA, YouTube, or Netflix, but they can see which sites you are accessing.

Why is CO2 added to carbonated water/soda and not other gasses? Why not add just air?

Originally beverages were carbonated via fermentation, which produces CO2 as the yeast. Some beverages still are done this way, such as beer. CO2 is still used because it's cheap and adds the acidic flavour. Some of the CO2 in the drink forms carbonic acid.

Air couldn't be used because it contains oxygen, which will allow for the beverage to spoil. Other gases can be used though. Guinness beer for example uses a mix of CO2 and nitrogen, giving it a more foamy head.

In general, for a gas to be used for "carbonation", it would need to:

* not cause the food to spoil (which is pretty much just oxygen)

* not cause some sort of undesirable chemical reaction with the beverage. CO2 will make some carbonic acid which is fine, but others may make more of worse chemicals.

* not have any negative odour or taste. You wouldn't want sulfur based gases that smell like rotten eggs.

* they would obviously need to readily dissolve in water. Helium for example would probably work fine, if you could actually get it to dissolve as well as CO2.

* not be flammable would be nice too, as even if methane (aka natural gas) or hydrogen could work, they would also be a little dangerous. 

* Also in the extreme, you wouldn't want it being poisonous. We add a little chlorine to water to kill bacteria, but you wouldn't want a rupture of chlorine coming out of a beverage or it will kill you. Lots of other toxic gases you wouldn't want in there.

* Again in the extreme end, you wouldn't want the gas to be a environmental issue. Something like SF6 may very well work, but you wouldn't exactly want a lot of that getting into the atmosphere.

A lot of gases wouldn't work for one of these reasons or another. I'm sure there's some other gas out there other than CO2 and to a lesser extent N2, they however most likely wouldn't be as cheap and easy.

What is the difference between noise isolating and noise cancelling headphones?


Noise Isolating

Consider the earphones that have earbuds in them. They block outside noise by providing a noise reducing barrier.

Noise Cancelling

Headphones that essentially listen to ambient noise and produce an opposite sound wave to blank out the unwanted sound. Fill your bathtub with water. Drop two rocks into the tub one at each end.  When the waves collide you will see a spot where the water seems calm because the waves are cancelling each other out. Noise cancelling headphones produce this negative wave by listening in to the outside noise and producing the opposite wave to cancel out the wave just like in the water.

Why are canned foods high in sodium? Doesn't canning eliminate the need for preservatives?

Not entirely.

First, depending on the food we're talking about, salt might be an inherent part of the process, either of canning in particular or just the food in general. Pickles? Olives? Gotta have salt. Salt is also a critical ingredient in any number of fermented foods, many of which are canned.

Second, salt is a flavor enhancer. Processed food manufacturers have tended to add loads of salt to a wide variety of foods for the better part of a century as a way of making their products tastier. Canned foods are hardly unique here.

Third, while canned vegetables are certainly saltier than their raw counterparts, they're not necessarily as salty as you might think. One 30g slice of white bread has a little less than three times as much sodium as 28g of canned green beans.

Fourth, while canning certainly tends to kill biological organisms, it's not magic. Some organisms are merely weakened. Some may even survive, though in small enough numbers that they can't cause a problem if the food is eaten within a year or two. A little salt goes a long way towards ensuring that fewer bacteria survive, and those that do stay dormant.

But lastly, bacteria aren't the only things that contribute to food spoilage. There are other chemical processes that have nothing to do with bacteria that can make food go bad, or at least lose quality over time. Discoloration comes immediately to mind, but that's not the only thing. Flavors can change. Textures can break down. Foods can take on flavors from their containers. Salt creates an environment inhospitable to bacteria, to be sure, but it also tends to interfere with some of these other processes, making it useful as a preservative even in a largely sterile environment.

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