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High Sierra and iOS 11

The release dates are here for some major updates to Mac OS, iOS 11 and watchOS 4. I have been playing with these throughout the beta period, and I think you’re going to like the new features and changes!

What’s New in macOS 10.13 High Sierra and Its Main Apps

Although Apple’s eye-catching Desktop image of the High Sierra mountains makes it easy to confirm that your Mac is running High Sierra, the most noteworthy new features are invisible! These changes are aimed at improving your Mac’s performance. But, don’t worry — you’ll find plenty to do in Apple’s apps, and we’ll share our favorite features below.

Apple’s invisible, under-the-hood changes modernize the Mac. The new APFS file system significantly improves how data is stored on your disk. It replaces the HFS+ file system, which dates from the previous century. You’ll notice the switch to APFS when you look up the size of a selected folder or duplicate a large file because the operation should run much more quickly. APFS also provides better FileVault encryption and reduces the chance of file corruption.

Also new is HEVC, a new video compression standard that will let videos stream better and take up less space on your drive, and HEIF, an image format that boasts significantly better compression to keep photos from overwhelming your drive. HEVC and HEIF have other advantages too, but they’re so embedded into High Sierra (and iOS 11) that all you’ll notice is more space. When you drag images and videos out of Photos, they’ll come out in familiar formats suitable for sharing.

Photos 3
In Photos, it’s now easier to browse your photos from the always-on sidebar on the left side of the window. Photo editing is also more streamlined, with the Edit screen now separated into three tabs: Adjust, Filters, and Crop.

You can now edit Live Photos! Look at the bottom of the Adjust tab for controls for picking any frame as the static “key” frame, trimming the video, and applying special effects. The most interesting effect blurs the Live Photo by turning the 3-second mini-movie into a single long exposure.

Those who are into tweaking photos by hand should check out the new Curves and Selective Color options on the Adjust tab. Or, if you’d prefer that your Mac do the heavy lifting, try the new filters on the Filters tab.

Our favorite new feature is more of a fix—when you train Photos to match faces with names, that training will now sync through iCloud Photo Library to your other Apple devices. About time!

Finally, for serious photographers, Apple has at long last brought back round-trip editing of a photo in an external app, like Pixelmator or Photoshop.

Safari 11
A new Websites tab in Safari’s preferences lets you specify Web sites that should always open in Safari’s clutter-reducing Reader View. This lets you block some ads and auto-play videos, set the zoom level on a per-site basis, and more. We like to tweak these options for the current Web page by choosing Safari > Settings for This Website to open a popover with the necessary controls.

And in the “Thank you, Apple!” category, Safari now offers Intelligent Tracking Protection (ITP), which limits advertisers’ cross-site tracking of where you’ve been online. We applaud Apple’s continued commitment to privacy protection.

Notes 4.5
Notes now offers a capable Table feature and a handy File > Pin Note command that puts the selected note at the top of its list rather than listing it by order last edited. Neither feature is earth shattering, but we’re enjoying both already.

Mail 11
Behind the scenes, Mail gets a welcome change you probably won’t notice: according to Apple, message storage now takes 35% less space.

More obvious is how Mail revamped its behavior in full-screen view. Instead of the message-composition area overlapping most of the Mail window, the screen splits, and your new message appears at the right. This layout simplifies viewing an older message while drafting a new one.

FaceTime 4
A fun new FaceTime option is taking a Live Photo of your call. It’s a perfect way to record mini-movies of far-away relatives. If the person you’re chatting with allows Live Photos in FaceTime’s preferences, hover over the FaceTime window to see and then click the round Shutter button.

Spotlight
Spotlight isn’t exactly an app, but it lets you search for anything on or off your Mac. Click the magnifying glass icon at the right of your menu bar—or press Command-Space bar—to start, and then enter your search terms. New in High Sierra, you can enter an airline flight number to see oodles of flight-related info.

Moving on to watchOS 4…

7 Great New Features in watchOS 4

With watchOS 4 now arriving on Apple Watch users’ wrists, it’s time to make sure you aren’t missing out on any of the important features—and to share a few tips for how to use them. watchOS 4 works on all Apple Watch models, even the original Apple Watch! It does require iOS 11, so if you’ve been using your Apple Watch with an iPhone 5 or 5c, you’ll need to stick with watchOS 3 until you get a new iPhone.

#1: Dock Scrolls Vertically instead of Horizontally
Press the side button to see the Dock, and you’ll notice that it now scrolls vertically—this makes sense since one of the ways to scroll it is by turning the digital crown. You can now arrange Dock items (using the Watch app on your iPhone) based on either your favorites or which Dock items were used most recently.

#2: Useful and Fun Watch Faces
The new Siri watch face doesn’t add new speech capabilities, but it does show timely information, pulling in personal details and suggestions from apps such as Calendar, Reminders, and Photos. It also shows Now Playing controls when you’re playing audio on your iPhone, along with Apple News headlines and stock tickers. We liked it more after customizing its Data Sources in the iOS Watch app.

When you want something whimsical on your wrist, there’s now a Toy Story face! Or, try the trippy new Kaleidoscope face that changes slowly as time goes by—you can speed it up by turning the digital crown!

#3: App List Supplements Icon Cloud
The App screen’s icon cloud looks impressive, but it can be challenging to locate and tap a specific app. We’re appreciating the new List view, accessed by force-pressing the App screen, which displays apps alphabetically.

#4: Flashlight on Your Wrist
Swipe up to find and tap the new Flashlight button in Control Center, which turns the screen bright white. Swipe left to access a flashing option, designed to make you more visible at night while walking or running. Press the side button or digital crown to turn the flashlight off. I have found this new flashlight feature very useful so far!

#5: More Fitness Encouragement and Options
The Activity app is now more chatty and will make suggestions in the morning to inspire you. It will also remind you at night if you are close to closing a ring.

Apple gave the Workout app some attention, too. Starting a workout is easier than before; it now requires only one tap, Do Not Disturb turns on automatically, and your default playlist can even start playing. With the workout underway, you can now switch easily to a different workout type (swipe right and tap the + button), and see a multi-workout analysis at the end of the entire session.

Swimmers using an Apple Watch Series 2 or 3 can now track sets and rests, pace for each set, and distance for each stroke type. Apple also has added a High Intensity Interval Training workout type.

Finally, your Apple Watch can connect with some gym equipment, like ellipticals and indoor bikes, allowing it and the machine to share data. Look for an NFC label on your machine, and tap it with your watch.

#6: Multiple Playlists On the Go
The Apple Watch is great for playing tunes to AirPods while you work out, but with watchOS 3 you were limited to just one playlist. With watchOS 4, you can sync multiple playlists and albums via the Music settings in the iOS Watch app. Plus, for Apple Music subscribers, your automatically generated favorites mixes can sync automatically!

#7: More App Enhancements: Phone, Timer, and Camera
Other apps also receive improvements in watchOS 4. You can dial phone numbers manually with a new keypad in the Phone app. Timer now has a Repeat button, so you can repeat a timer with a single tap. And the Camera app offers some new remote options, including support for starting and stopping videos.

All-in-all, watchOS 4 is a solid upgrade, and the changes will make your Apple Watch both more useful and easier to use!

The Top Features You’ll Want to Try in iOS 11

Even if you’re not buying a new iPhone this year, you can still enjoy a hefty dose of “New and Improved!” with Apple’s iOS 11, which provides a host of new capabilities. Hold on tight, there’s a lot to cover, and we have even more below about the iPad-specific changes in iOS 11.

Getting Started
After you install iOS 11, you’ll notice a few things right off. Dock icons no longer have names, and many Apple apps now have the bold text design Apple brought to the Music and News apps in iOS 10.

Although the new Automatic Setup feature won’t help you today, when you next get a new iOS device, it can transfer many settings from an older iOS 11 device automatically. Similarly, the new Share Your Wi-Fi feature lets you send your Wi-Fi network’s password to another iOS 11 device that tries to connect.

You may not need a new iPhone or iPad anyway, since iOS 11 can help you recover precious space! Choose Settings > General > iPhone/iPad Storage and you can offload unused apps (while keeping their settings and data), delete old Messages conversations automatically, and see how much space each app consumes. Deleting music from the Music sub-screen (tap Edit) will help too.

Special Screens
Apple redesigned Control Center, which most people still get to by swiping up from the bottom of the screen (iPad users keep swiping up after the Dock appears, and iPhone X users will have to swipe down from the right-hand top of the screen). It’s back to a single page of icons, and you can access additional options by pressing and holding on any set of controls. Even better, you can add (and remove) controls in Settings > Control Center > Customize Controls. I have added handy things like HomeKit, Hearing and Magnification to my Control Center.

The Lock screen is all you’ll see while in the car by default now, thanks to the Do Not Disturb While Driving feature. It blocks notifications and prevents you from using your iPhone while at the wheel, all while auto-replying to people who text you. Calls still come through to your car’s Bluetooth system, and texts from people designated as favorites can break through the texting cone of silence. Passengers can disable Do Not Disturb While Driving easily from a notification on the Lock screen. This is a great safety feature! I cannot tell you how many times I have passed a car on my motorcycle that is acting erratically only to glance in to see the driver texting.

Smaller Changes and App Updates

A few smaller changes that you’ll appreciate include:

Siri sounds more natural, can do translations, and uses on-device learning to understand you better and provide more useful results.
On an iPhone, a new Emergency SOS feature will call 911 and notify your emergency contacts of your location after you press the Sleep/Wake button five times quickly and swipe the Emergency SOS button. Tap Settings > Emergency SOS to set this up.
The password auto-fill feature now suggests stored login information for many apps right from the QuickType bar above the keyboard—manage this in Settings > Accounts & Passwords > App & Website Passwords.

Many of iOS 11’s built-in apps receive significant changes as well:

Camera: New file formats will make your videos and photos take up less space. There are a few new filters, and Camera can finally scan QR codes, which simplify loading Web sites, getting contact info, and connecting to Wi-Fi networks.
Photos: You can now edit the video in a Live Photo and apply looping, bouncing, and long exposure effects. Photos can at long last play animated GIFs and has a new Animated smart album to hold them.
Files: This major new app replaces the iCloud Drive app. Look in Files for access not just to iCloud Drive, but also to files on your device and in other cloud sharing services like Dropbox and Google Drive.
Messages: A new app drawer at the bottom of the screen tries to entice you to use iMessage apps. Most are just stickers, but some are useful and Apple provides a new Apple Pay app here that lets you make person-to-person payments.
Maps: Apple has added indoor maps of some airports and malls to Maps. Maps also now provides lane guidance on more complicated roads.
Notes: The new Instant Notes feature make starting a note as simple as tapping the Lock screen of an iPad Pro with an Apple Pencil, or the optional Notes button in Control Center. A note can now look like lined paper or graph paper (tap the Share button, then tap Lines & Grids). You can also now scan a document. The idea is that you then sign it with the Apple Pencil and send it on its way. Notes can also now find text in Apple Pencil handwriting.

Take some time to explore—we’re liking these new features and we think you will too!

Why iOS 11 Is the Most Important Version Yet for iPad Users

Apple has long argued that you can use the iPad for productivity but hasn’t backed that claim up with the necessary features in iOS. Until now, that is, with the new iPad-centric capabilities of iOS 11. These changes mean that an iPad running iOS 11 is more like a Mac, and that’s a good thing for those who want to do real work with their iPads.

Dock and Multitasking
The new iOS 11 Dock is easy to find at the bottom of the Home screen, just like before. But it’s better and more Mac-like than before—the left side shows apps or folders you’ve placed there by dragging them on (no need to touch and hold until icons shake anymore!) while the right side helps you get around more quickly by displaying recently used apps and any Handoff apps from your other Apple devices.

Most importantly, you can now view the Dock within any app, without the contextual shift of returning to the Home screen as in previous iOS versions. Just swipe up slightly from the bottom of the screen in any app, and the Dock appears so you can switch apps with a single tap right away.

Or—this is fabulous!—drag the app where you want to go up from the Dock to open it in Slide Over or Split View. Now you can work back and forth between two apps at once on the same screen.

Control Center and App Switcher
Switching apps with the Dock like you do on the Mac is easy, but when you invoke the App Switcher by swiping up to see the Dock and then continuing to swipe up (or by double-pressing the Home button or swiping up with four fingers), it now shows large thumbnails of the four most recent apps (or Slide Over or Split View screens) and the new Control Center. Tap one to switch to it.

Remember that you can customize the buttons that appear in Control Center—visit Settings > Control Center > Customize to make it look the way you want.

Drag and Drop
With iOS 11, Apple finally brought drag and drop to the iPad! Touch and move text, graphics, or files between apps—you can even pick up an item with a finger and use your other hand to reveal the Dock and switch to your destination app before dropping the data.

Use this maneuver in situations where you would previously have used copy and paste or the awkward Share sheet—or just given up! Practice a few times to accustom yourself to the two-handed process.

Files
Just like the Mac, the iPad now provides a single place to browse and open all your files, and you can open a file with a single tap. All this goodness happens in the new Files app, which replaces the iCloud Drive app with a broader view of your files, providing access not just to iCloud Drive, but also to files on your device and in other cloud sharing services like Dropbox and Google Drive. (To add a sharing service whose app you’ve installed, tap Edit in the left-hand Browse panel).

Keyboard Flick
On iPads other than the 12.9-inch iPad Pro, iOS 11 simplifies typing on the virtual keyboard. You can now type numbers and many punctuation characters by swiping down on the appropriate key, rather than switching keyboards. Swipe down to see the key turn gray and show only the desired number or character, and then lift your finger.

Apple Pencil
In iOS 11, the iPad Pro’s Apple Pencil becomes even more useful. Want to start a note? Just tap the Lock screen and start writing. Want to search your handwritten notes? Pull down on the Notes list to type your query, and Notes will find handwritten terms.

A new scanning feature in Notes makes it easy to bring a paper document into the iPad, where you can sign it with the Apple Pencil and send it on its way. We also like the new Instant Markup feature that lets you write on a PDF or screenshot easily—tap the Pencil icon at the upper right of the screen to start writing and to access the controls for color and tip below.

With iOS 11, Apple has finally acknowledged that the iPad needs its own features to be a productivity machine—it’s not just an iPhone with a larger screen. With a little practice, you can be using an iPad, particularly an iPad Pro, for all sorts of serious tasks, like email, word processing, Web research, and more.

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Apple Pencil

I am by no means an artist nor someone who has drawn anything beyond your standard High School art class. However something drew my attention the Apple Pencil, call it intrigue or even memorization of the new slick addition to the Apple line up I could not keep from considering why it was so endearing. Whatever the calling was I finally made up my mind and purchased one of these compelling little stylus, and boy oh boy was I impressed. I had little experience playing with the abilities of the Apple Pencil outside of the store. I have discovered a new found obsession with sketching.

For anyone who has ever drawn with your standard paper and pencil, (as well if you are as nit picky as I am) you will quickly find by erasing multiple strokes several times you quickly create this indent on the paper, an indent that will never go away. This is infuriating! As with any drawing tablet this frustration is elevated when using a computer to render your work allowing easy (Command – Z) undo functionality. There are some intense differences when comparing drawing tablets vs paper and pencil, and many artists strongly dislike the separation between the two. Again, I am no artist and do not claim to have a strong history with any of the options discussed. However I must express my complete and wonderful surprise that was using the Apple Pencil. The fluidity, precision and pencil likeness was unmatched by any expectations I had. Whether it be lightly sketching out the initial point of reference lines or deeply highlighting the final details it feels as though I am sketching on a piece of paper just underneath the glass of my iPad Pro.

Without spending all day going into details and further examples, I’ll wrap this up with a final thought. The Apple Pencil is not just for Artists, or people in the field of artistry. If you are someone who draws, sketches, paints or even prefers written notes, the Apple Pencil can be another tool added to the arsenal. Even if you are like me, someone who has never tackled anything artistic but has a nagging urge to create, I highly encourage swinging down to Small Dog and testing out the Apple Pencil. We have one at the counter anyone can test out on one of our iPad demo models and see for yourself what makes it such a unique and diverse product.

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AC Rectification

It’s back to usual this week for my article, because I thought of a good topic. I’ve talked many times about AC power and how and why we use it, but many things don’t use AC power. In fact, they can’t. These are things we use every single day. Virtually all digital electronics cannot use AC power directly. It needs to be converted into DC power. Remember that AC means the current is alternating and DC means the current is flowing in one constant direction.

Any time you convert electricity from one type to another, or one voltage to another, there will be losses. Nothing is free. Every time you change something about electricity, you have to pay a tax. The goal in electronics design is to minimize those losses. AC to DC conversion is one of the simplest and most efficient conversions we do on a regular basis. DC to AC conversion is also possible (accomplished by inverters). Most of these processes are on the order of 95% efficient or greater. So how do we convert AC to DC?

First off, the process of converting AC to DC is called rectifying. Devices that accomplish this task are often called rectifiers. A very common rectifier design is called a bridge rectifier. To understand how they work, we have to recall that AC is a wave. Sometimes it’s voltage value will be positive, other times it will be negative. This doesn’t work for DC since the voltage has to always be positive or always be negative. Rectifiers take the negative voltage swing of the wave and flip it up top so that it’s positive. Now instead of a sine waveform, the output of the circuit will look like mountains. The voltage will always be positive, but it will still vary considerably, from the peak (approximately 170 volts on grid-level 120VAC) to zero and then back up again.

How is the voltage rectified? In a bridge rectifier a ring of diodes is used. Recall that a diode only allows current to flow through it in one direction. By arranging the diodes in a ring we can create a “draw off” point for the current where the voltage will always be positive. Instead of being allowed to “pull” the current backwards during the negative voltage swing, the diodes redirect it back to the output point. Of course, this only means that the negative voltages get flipped up, creating the mountain-like waveform I mentioned earlier. This is not good for DC power, so how do we fix it?

There are many ways to minimize this issue, but it can’t be fixed perfectly. One way is to use capacitors to buffer the output voltage. Instead of sinking when the mountains go back down to zero, the capacitors prop the voltage up during that period, until the next mountain peak arrives. Depending on the load, this could mean large capacitors to hold the load long enough. Remember also though that AC has a frequency on the order of 50-60Hz. This means there will be around 120 of those mountain peaks every single second, so the capacitors don’t need to hold for too long.

The other issue we have to contend with is how to reduce the voltage from anywhere between 120-240VAC to something DC electronics might expect, like 5VDC. For AC to anything, this is actually very easy; we use transformers. A transformer has two sets of wire windings, a primary winding and a secondary winding. The primary winding contains the input current, usually fluctuating AC. This fluctuating current induces a magnetic field that also fluctuates in a metal core that extends from the primary winding to the secondary winding. The changing magnetic field in the core induces a new current in the secondary winding. The induced current will necessarily be greater than the input current if the windings are configured to reduce voltage. The overall power has to remain the same. So if the input were 120VAC at 1 amp (120 watts), and the transformer was reducing the voltage by a factor of two, the output would be 60VAC at 2 amps (still 120 watts). The output of a transformer will still be AC, but this is where we would apply rectification.

This method of power conversion is extremely efficient, but as transformers are highly inductive, power companies would hate it if every single device used one. The reason for this is because inductive loads shift power around a lot without actually consuming that much. So the power company has to pay to send the power all the way from their generating station, to you, only to have your device reject almost all of the actual energy in that power. Most homes don’t have solely inductive loads though, so most of the time it’s not an issue. However, certain industrial processes rely heavily on inductive load machinery. In these cases, the power company may request that they burn off a certain amount of power in dump loads (basically huge resistors) in order to keep the grid functioning normally.

So there you have it. How we take that high voltage raw AC power from the wall and tame it to safely power all of your devices.

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Heading Into The Library Stacks

I remember way back when, that Grace and I would go to the Chicago Public library to “do our homework”. When we actually did some homework the reference section was my favorite. That and looking at the huge microfiche library of old copies of the Chicago Tribune.

Did you know that Apple hid a huge reference library in your Mac?

You’re probably used to Mac apps using red underlines to mark misspelled words, but did you know that macOS has long included a fully-featured Dictionary app as well? It provides quick access to definitions and synonyms in the New Oxford American Dictionary and the Oxford American Writer’s Thesaurus, along with definitions of Apple-specific words like AppleCare and MacTCP. But that’s far from all it can do.

First, let’s make sure we’re all on the same page. Launch the Dictionary app from your Applications folder and then type a word or phrase into the Search field. As you type, Dictionary starts looking up words that match what you’ve typed so far—you don’t even have to press Return. If more than one word matches what you’ve typed, click the desired word in the sidebar.

Notice the lozenges below the toolbar, representing the references that Dictionary can consult, and no, your eyes aren’t deceiving you—Dictionary can look things up in Wikipedia if your Mac has an Internet connection. In short, Dictionary gives you instant access to a dictionary, a thesaurus, and an encyclopedia containing over 5.4 million articles in English alone! You can click a reference’s lozenge to limit your search, or select All to scan all of them.

If you want to look up words in another language, or even just British English, Dictionary has you covered, with a long list of other reference works. Choose Dictionary > Preferences and select those you’d like to use. You can drag the selected entries into the order you want their lozenges to appear below the toolbar.

Once you’re in a definition, note that you can copy text for use in other apps—always helpful when wading into grammar and usage arguments on the Internet. More generally, you can click any word in Dictionary’s main pane to look it up instantly. If dictionaries had been this much fun in school, we’d have larger vocabularies! Use the Back and Forward arrow buttons to navigate among your recently looked-up words.

As helpful as the Dictionary app is, you probably don’t want to leave it running all the time. Happily, Apple has provided quite a few shortcut methods for looking up words:

  • Command-Space to invoke Spotlight, and enter your search term.

  • Select a word, and then choose AppName > Services > Look Up in Dictionary to launch Dictionary and search for that word. This trick should work in most apps, but won’t work in all. If the Look Up in Dictionary command doesn’t appear, make sure it’s enabled in System Preferences > Keyboard > Shortcuts > Services, in the Searching category.

  • Last but best, hover over a word or phrase with the cursor and either press Command-Control-D or Control-click the word and choose Look Up “word.” If the app supports it, macOS displays a popover with the definition or Wikipedia article. If you have a trackpad, you can also do a force-click or three-finger tap on the selected word—make sure the “Look up & data detectors” checkbox is selected in System Preferences > Trackpad > Point & Click.

Now that you know how to take full advantage of the reference library that Apple has built into macOS, it’s time to get in touch with your inner logophile (feel free to look that one up).

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Stay Cool

Summer officially started this week. Has anyone checked with Mother Nature? Are we sure she got the memo? Seriously, sometimes I can’t tell where we are with the weather. I don’t really mind the hot weather at all, as long as I can do things like jump in a river, or ride my bike. The warmer days had me thinking about an interesting topic that spans a bit more than just electricity and magnetism, but I thought it might be interesting anyway. How do we cool things down?

I’ve always been fascinated by this actually. Even as a child, I could understand, heating things up was easy. Fire is easy. Warming myself up in winter with a heavier jacket was easy. Cooling things down is always trickier, and there are several ways to do it. To get a better understanding of how we cool things down, we have to start at the very basics. What is temperature? Actually, what we call temperature is a measure of motion, specifically of atoms and particles. They’re not moving from A to B, but rather, vibrating in place, or in the case of gases, moving around haphazardly. The faster they move, the higher the temperature of the substance. When all motion stops, the substance if brutally cold. So cold, in fact, that it has a special name: absolute zero. Absolute zero is approximately -273.15 Celsius or -459.67 Fahrenheit. We even have a temperature scale that starts at absolute zero, called the Kelvin scale. 0 Kelvin is absolute zero. The motion of the atoms or particles also gives off something called black body radiation. This is simply thermal-spectrum electromagnetic radiation. As such, it’s part of the electromagnetic spectrum I wrote about some time ago. This is how infrared cameras work as well as any thermal imaging camera.

With that background in place, it’ll make more sense when I explain certain cooling methods we commonly use. One of the most efficient and effective cooling methods is gas decompression. This is how nearly all refrigerators, air conditioners and heat pumps work. In any gas, the molecules comprising the gas are spaced pretty far apart. When you compress them into a tinier volume of space, the gas will increase in temperature. Is this because the particles are now hitting each other more often and creating more frictional heating? It would be nice if that’s how it worked, but it’s actually a bit more complicated than that. The simplest way to understand heating of compressed gas is to understand conservation of energy. Energy cannot be created or destroyed. Compressing a gas requires some amount of energy, and that energy has to go somewhere. It ends up going into the gas causing the particles to move faster, which we observe as heat. From a physical standpoint, the gas particles are interacting with the boundaries of their space more frequently as the space containing them shrinks. The most scientifically accurate explanation of the temperature increase is that by reducing the available volume of space, you’re increasing your theoretical knowledge of where each particle is. Instead of being somewhere in a huge volume of space, each particle is now in some much smaller volume. You’re decreasing the entropy of the gas. That knowledge doesn’t come free though. The particles essentially say, “ok, we’ll let you know more about where we are, but in turn we’re going to let you know less about our speeds, because we’re going to move faster.”

Whew…all of that. Are you still with me? Hadley, you haven’t mentioned a single thing about cooling yet! Just heating! Yes, but now all the pieces are available. When we compress a gas, it heats up for the reasons stated above, but we can do something with that heat. We don’t have to let the gas just stay hot. This is what refrigerators do. Once they compress a gas, they pass it through some type of heat sink. This is a device that allows the heat of the gas/fluid inside to dissipate as quickly as possible to the ambient environment. Once this happens, we have a roughly room temperature compressed gas. If we allow the gas to decompress, its temperature will fall…to below room temperature. The particles are now saying, “ok, you’re increasing our volume, and this means you’ll know less about where we are. So to compensate, we’ll slow down a bit so you can at least know how fast we’re going.” Obviously the trick in any of these refrigeration systems is being able to compress the gas a lot as well as being able to efficiently remove the heat from the compressed gas.

This process will work for any gas, including air. In fact, I encounter this phenomenon every time I air down the tires on my bike. The tires are filled with ordinary air, compressed to between 90 and 110 PSI. When initially pressurized, they do heat up, but over time, they cool to ambient temperature. When I rapidly release the pressure, the valve becomes noticeably cold to the touch. In most refrigeration, we don’t use air, we use some kind of refrigerant, like Freon. Freon is the trademark name for any number of different gasses used as refrigerants known as halocarbons. You’ve probably heard of at least some of these by their scientific name, chlorofluorocarbons (abbreviated CFCs). These are the same CFCs that scientists discovered were causing ozone depletion in the 1980s and 1990s, so they aren’t in widespread use anymore. All refrigerants are just special types of gas that have properties that are beneficial to what we’ll be doing with them.

The important thing to remember is that if you’re unable to remove the heat from the compressed gas, and you let it decompress, all it will do is decrease back to roughly room temperature where it started. So it won’t be cool the way we want it. If you want the gas to be very cold, you have to make its starting temperature less. There is actually no limit to this (beyond absolute zero) and this is how we create extremely cold substances like liquid nitrogen. In fact, you can sometimes create bits of dry ice (frozen carbon dioxide) by releasing a fire extinguisher into a burlap sack. The CO2 in the fire extinguisher is compressed, and if it’s been sitting long enough, it’s also at room temperature. Releasing the pressure causes a large decrease in temperature. So large that the gas actually solidifies into its solid state.

Hopefully this was an interesting slight deviation from my usual topics of electromagentism.

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