“The only thing that truly matters in public speaking is not confidence, stage presence, or smooth talking. It’s having something worth saying.” This is from Chris Anderson’s book, TED Talks: The Official TED Guide to Public Speaking. — MF

A whole book (“Influence” by Robert Cialdini) on the key scientific principles of how to persuade people — get them to change their mind or behavior — has been expertly compressed into a 12 minute doodle video. It’s so compressed you might need to review The Science of Persuasion more than once. The principles work! — KK

Scan almost any textbook math problem with your phone’s camera and Photomath will generate a step-by-step solution instantly. The app works for iOS and Android and it’s free. — MF

The best way to learn how to tie a knot: visit Animated Knots. Choose left- or right-handed, any direction. — KK

A good Reddit thread I learned a lot from, and one I hope will keep going: “What are some recent scientific breakthroughs/discoveries that aren’t getting enough attention?” — KK

For the past 8 years Sci-Hub has been the Napster of academic papers. It’s a pirate site that serves up scholarly journal articles usually stashed behind paywalls. You copy and paste the link from the official journal site (or its DOI) into the Sci-Hub website and it immediately gives you the PDF. I have no qualms using it. Many researchers who have legitimate access to the journals prefer to use Sci-Hub because its interface is easier, consistent, and better designed. — KK

My 16-year-old daughter and I are interested in learning about artificial intelligence, and we found a YouTube series produced by Google that has easy-to-understand examples that you can program yourself using the Python programming language. The first program we wrote was only 6 lines long, but it can tell the difference between an apple and an orange. — MF

When making toys, I refer to 507 Mechanical Movements. This old book is sort of a periodic table of known mechanical movements, first published in 1868. The book has been scanned onto the web, with many of the gears animated into looping gifs so you can see exactly how their ingenious mechanisms work and what movements they create. Just paging through this amazing 507 Movements website fills me with ideas. — KK

I came across some great advice on a Twitter thread which asked “What are some non-obvious ideas that can change your life?” @noahlt answered: “Shrink the quantum of experience: instead of reading a book, read a wikipedia article. Instead of eating a cup of ice cream, eat a spoonful. Decreases turnaround time, which both reduces procrastination and also allows me to decide whether I want to go deeper.” This tip encourages me to follow my curiosity, but reminds me to start with small bites. — CD

This iPhone/iPad app does just one thing — it gives you a feel for the fourth dimension by moving from 0 dimensions to 4. I’ve had this jewel of an app on my phone for years and still open it from time to time. It’s a great companion to Flatland. — MF

This well-done 3-part YouTube series by SmarterEveryDay will make you smarter about how/why social media algorithms are exploited, and why it is so difficult to remedy, and why this will be an on-going arms race. — KK

The best way I’ve found to understand a very technical or scientific paper is to search YouTube for someone to explain it. The ideal is to find a journal club report. Journal clubs are informal groups who share the task of explaining an interesting paper to each other. Each member rotates in picking a paper to explain to their peers. This is 100 times better than having the author explain it, because authors assume too much prior knowledge. It is better to have a newbie who just figured it out. If you are lucky, a journal club will video their reports and post. Search YouTube with the paper’s title or topic and add the term “journal club.” — KK

I’ve stumbled upon these ten little drawings of happiness practices all over the internet, and they still make me happy. I like learning untranslatable words that stretch the imagination. My favorite from this set is the idea of forest bathing. — CD

Shortbooks.co is a search engine for books that estimates reading time to help you find the shortest book on any subject. It’s not flawless, but you can never have too many book search tools. — CD 

Parallettext.io is an online tool that helps you learn languages by reading a book in a foreign language with your native language side-by-side. You can click on any sentence to hear it out loud. I’m not sure how helpful it is to learn an entirely new language, but it’s useful for me to read in Spanish from time to time to remind myself of how sentences are structured differently. Right now, I spend a little time each day working my way through Alice in Wonderland. — CD

One of the things I miss about the 1980s was writing programs for fun in BASIC. A couple of years ago I started playing around with Python. It’s easy to learn, and powerful enough to do anything I would want to automate. Christian Thompson’s YouTube channel has wonderful Python tutorials for beginners. Check out the one on how to program a Pong clone. — MF

Last week my friend texted to tell me that 4 planets were visible and I should go outside to check them out. I was only able to see 3, but I found them quickly with the beautifully designed SkyView app ($1.99, also on Android). I just held my phone up to the sky and SkyView pinpointed where they were precisely. For the occasional stargazer this app is more than enough. — CD

Part 1: Here’s an easy way to approximately convert Centigrade to Fahrenheit: “double the Centigrade temp, subtract the first digit of the result from the result and add 32.” Example: 16 C = (32-3)+32 = 61 F. (This tip is from Fodor’s Travel website.) — MF

Part 2: Recomendo reader Don wrote to tell us, “Your Centigrade to Fahrenheit conversion works ‘sorta’ as long as the result of doubling the C number is a two-digit number. I’ve always doubled the C number and subtracted 10%, then added 32. Most folks can figure out 10% and subtract it. Also, this doesn’t result in an approximation, but the correct result.” — MF

Part 3: The US is basically the only country in the world not using metric. It’s not that hard to learn a rough sense of how many kilometers in a mile, or pounds in a kilo. But it is very hard to convert temperatures between Centigrade and Fahrenheit. The solution is to convert all your thermometers to Centigrade: on your phone, in or outside of your house, on websites. Have any digital device display only Celsius, so you can’t cheat. In about a year, you’ll have a reliable and native sense of what’s cool and warm in degrees C. This is supremely handy if you travel anywhere outside of the US. — KK

You can’t win fairly at carnival games, because they aren’t fair. Here’s a great fun tutorial that teaches you a few tricks for the ones you might win. — KK

I’ve been building 3-string guitars for about 10 years. It’s easy to do and they sound better than you probably think. Learn how to make one at Cigar Box Nation. They are even easier to play. Here’s a 10-minute video that will have you sounding like you know what you’re doing. — MF