Atmosphere of Earth Updated +Created
BB(6) is hard Updated +Created
wiki.bbchallenge.org/wiki/Antihydra:
BB(6) Updated +Created
PROMYS Updated +Created
The good:
The bad: everything else. Closed source learning materials + a university-like selection program. Such a waste of efforts that could benefit way more people with more open resources.
meta.mathoverflow.net/questions/4889/request-to-keep-an-eye-out-for-promys-admissions-problems asking to remove PROMYS problems from MathOverflow. And it seems to have been mostly accepted. Newbs. Any maths problem should be allowed to be askeable online. There are no fundamentally new problems, copyright takedown is just silly.
Standing wave Updated +Created
Figure 1.
Standing wave caused by wave interference of two waves
. Source.
Pre-university summer school Updated +Created
Plucked string model Updated +Created
Staring from a triangle wave, this explains why we always get the same musical notes:See also: solving partial differential equations with the Fourier series.
TODO: do higher overtones decay faster in time than the base ones?
Video 1.
Motion of Plucked String by Dan Russell
. Source.
Video 2.
Slow motion: rubber string pulled and released by Pavel Radzivilovsky
. Source.
Good symmetric example. But unfortunately the video is too short.
Wave equation on string with one vibrating side Updated +Created
Video 1.
Modes on a String by geoff martin
. Source.
Wave equation boundary condition Updated +Created
Damped wave equation Updated +Created
Summer school Updated +Created
Extracurricular activity Updated +Created
You know things are bad when the extracurricular activities are what studnets should actually be doing full time instead!
Benzene Updated +Created
Video 1.
The FASCINATING 200-Year History of Benzene by Chemistorian
. Source. Interesting history. Notably how things were only finally well settled by X-ray crystallography.
List of organic compounds Updated +Created
Argon-40 Updated +Created
K-Ar dating Updated +Created
Discovery of the noble gases Updated +Created
Discovering them was not so easy because they don't form chemical compounds. So they exist only as gases. And Helium disperses off into space.
Argon was the first to be found by density considerations because it is so abundant on Earth's atmosphere (~1%): Argon is abundant on Earth's atmosphere because it comes from the decay of Potassium-40.
Then basically all of the others were discovered by spectral lines. Helium notably was first found on the Sun like that, and only later on Earth! Thus its name. Pretty cool.
Video 1.
The Incredible Discovery of the LEAST Reactive Elements by Chemistorian
. Source. 2024. Great video.
Coq (software) Updated +Created
Argon isotope Updated +Created

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