Blog

A traditional blog post can be thought of as residing in a network, with webpages linking to and from it. However, if one were to naively consider every incoming and outgoing link to this webpage, it can become a bit chaotic. This series is my humble attempt to manually curate a network (a ‘roadmap’) with interesting content from the internet along with my own commentary as needed. This will hopefully serve as a compass to those who wish to navigate the information superhighway.

Roadmap

Double-click on any box to view its contents.

Nodes:

2015-2019

The physicist Leo Szilard once announced to his friend Hans Bethe that he was thinking to keeping a diary: “ I don’t intend to publish. I am merely going to record the facts for the information of God.” “Don’t you think that God knows the fact ?” – Bethe asked. “Yes” said Szilard. “He knows the facts, but He does not know this version of the facts”

This section contains exploratory blog posts that I wrote during 2015-2019 on things that I learned and tried just for the fun of it across a few different blogging platforms. I wrote most of these posts when I was pursuing an undergraduate degree in engineering, so they might have a strong flavor of ‘This is why it works or This is why it’s cool’. Feel free to look around and if you find anything interesting and would like to discuss, contact me via email (153armstrong@gmail.com) or post a comment below.

A lot of people have helped me on this venture over the years and I am deeply grateful for the insightful discussions that I have had with all of them.

Fluids

  1. Buoyancy
    1. Origins of the Buoyant force
    2. How do hot air balloons work?
    3. Note on average density and how do ships not sink?
  2. Flow Instabilities
    1. Plateau- Rayleigh Instability
  3. Pilot Wave Hydrodynamics (completed with Nicole Sharp, FYFD)
    1. Introduction
    2. Chladni patterns
    3. Faraday instability
    4. Walking droplets
    5. Droplet lattices
    6. Quantum double-slit experiments
    7. Hydro single- and double-slit experiments
    8. Quantum tunneling
    9. Hydrodynamic tunneling
    10. De Broglie’s pilot-wave theory
    11. Resources and references on pilot wave hydrodynamics
  4. Others
    1. How to photograph shock waves?
    2. Ultrasonically levitated water droplets
    3. Catching prey using vortices
    4. Whale Flukeprint
    5. Estimating the energy of an atomic bomb using dimensional analysis

Physics

  1. Astronomy
    1. Measurements
      1. How far away is the moon and lunar laser ranging experiment
      2. Parallax method, 61-Cygni and the Hipporcas mission
    2. How to use the hubble legacy archive (HLA) – 101
    3. The Chandler wobble
    4. On the orbital plane
    5. Supernova Sorcerer: Robert Evans
    6. A note on the Hydrogen spectrum
    7. On the strong 5577Å spectrum line
    8. Celestial wonders – Binary stars
    9. Dropping a feather on the moon
    10. Saturn’s hexagonal cloud pattern
    11. Beauty of eclipses on earth
    12. On disappearing shadows of Birds and airplanes
  2. Classical Mechanics
    1. So. this is called blobbing
    2. The simple harmonic oscillator
    3. Using complex numbers in classical mechanics
    4. Remembering the Laplacian in different coordinate systems
      1. Jackson’s form of the laplacian in spherical coordinates
      2. Solving the Laplacian in spherical coordinates
    5. Euler-Lagrange equation for a classical field
    6. Cooking up a Lorentz invariant Lagrangian
    7. Length contraction , Time dilation and Lorentz Transformation: Pokemon edition
  3. E&M
    1. Chocolate bar in Microwave(#1)
    2. Chocolate bar in Microwave(#2)
    3. On Diffraction and the Helical structure of DNA
    4. On Optical Tunneling and Evanescent waves
    5. Diamagnetic Levitation -Ig Nobel prize (2000)
    6. A note on levitating frogs and superconductivity
    7. Can you crush a soda can with lightning ?
    8. Pokemons and bioelectricity
    9. The holy grail of Electromagnetic Radiation
    10. Combinatorics and the two state paramagnet
  4. Chaos
    1. Chemical Turbulence : Belousov Zhabotinsky reaction
    2. Dynamics of Love affairs:  Valentine’s Day Gift Box
  5. Quantum Mechanics
    1. Commutation relation in QM (using Index notation)
    2. A note on what makes solutions discretized?

Math

  1. Feynman’s trick
    1. Intro to parametric integration
    2. Using Feynman’s trick on Laplace transform problems
    3. Feynman’s trick applied to Contour Integration
  2. Differential equation
    1. Legendre Differential Equation (#1)
    2. Legendre Differential Equation (#2)
    3. Legendre Differential Equation (#3)
    4. Legendre Differential Equation (#4)
  3. Beautiful proofs
    1. Divergence of the harmonic series
    2. Euler’s Sum
    3. Area under a sine curve
    4. When Gauss was a young child…
  4. Number and Graph theory
    1. Homeomorphic Irreducible Trees with 10 vertices
    2. Divisibility tests
    3. Holy matrimony of Pascal and Sierpinski’s triangle
    4. Geometric series formula
    5. The tale of taylor series coefficients
    6. Division by 7
  5. Pi-day
    1. How did the Greeks know that pi=3.14?
  6. Others
    1. Why is (-1) x (-1) = +1 ?
    2. Why is 1+1 = 2 ?
    3. Only Time will tell – A Complex Number Tribute.
    4. Complex numbers are not complex
    5. Basis vectors are instructions
    6. The generalized product rule (Leibniz formula)
    7. Finding n roots of unity
    8. Never forget De Moivre’s formula
    9. Caustics
    10. Curves of constant width
    11. On the direction of the  cross product
    12. The Knight’s tour
    13. The geometry of a pringle

Engineering

  1. Themed adventures
    1. Up, up and away
      1. The magnus effect
      2. Introducing the wind-tunnel
      3. Flight dynamics : Pitch , roll and yaw
      4. Physics of “stall”
      5. On Taj Mahal and lift in airplanes
      6. Vortex Generators ( How inducing a vortex helps an aircraft )
      7. Wingtip vortices  ( The why and how about wing tip vortex )
      8. Have you heard about the popular y250 vortex on a F1 car? It’s amazing!
      9. Von Kármán vortex street
      10. Aerodynamic Flutter
      11. Landing on aircraft carriers
    2. 3.5 mm headphone jack
      1. Preparing a headphone jack for hacking
      2. Every speaker is also a microphone
      3. The Anatomy of a headphone jack
      4. How does a computer know that you have plugged in a jack ?
      5. Testing basic headphone jack functions (Android)
      6. Don’t do this! – Headphone jack
      7. Speaker Impedance and the Headphone jack
      8. Vibration motor meets the headphone jack
      9. LiFi using solar panel and headphone jack
      10. LiFi using IR sensor, Arduino and headphone jack
      11. Really simple “mobile phone detector” using headphone jack
      12. Lightning detector with nothing more than a simple headphone jack
      13. Headphone jack meets a spark gap
      14. Detect switching ON/OFF of Tube-light with a simple headphone jack
      15. Cigarette Lighter spark detection using headphone jack
      16. Transmitting in the RF range using the headphone jack
      17. Listening to radio signals from a remote control car using a headphone jack
      18. Obstacle detector “with audible feedback” using headphone jack, IR sensor and 555 timer
      19. How does a selfie stick work?
  2. Train, Flights and cars
    1. Flight
      1. What Is That Hole in the Tail of an Airplane?
      2. Why do pilots use non polarized sunglasses ?
      3. Reverse Thrust
      4. Supersonic shock diamonds
      5. The radial engine
      6. Variable sweep aircrafts
      7. The Joukowski transform
      8. Vapor cones
    2. Rockets
      1. How to turn during flight ?
      2. Why do shuttles orient belly up after a launch ?
      3. Spin stabilization
      4. How do you place a satellite in orbit?
    3. Pantograph and Trains
    4. This is a Dragster Blowover
    5. UV light, Thou shall not enter!
  3. Technology
    1. The Touch Screen
    2. ‘Hook and Loop’: The fascinating tale of velcro
    3. That’s how a revolving fan works
    4. ABS – Anti-lock braking system
    5. Why are there rivets on your jeans?
    6. Making images from pixels
  4. Others
    1. Walter lewin chalk trick | 1000 fps
    2. Why do shower curtains encroach your showering space ?
    3. Can dominos knock down the empire state building?
    4. Types of damping
    5. The Miura fold : Making flat surfaces smaller
    6. Powering a 13W CFL bulb using a 3V battery
    7. Square wheels on cars?
    8. De-constructing Backyard Brain’s TED talk
    9. Why can’t you cycle backwards?
    10. Baby powder and fire breathing
    11. Why do bullets spin when they leave the barrel ?
    12. Polish a surface well enough and you can turn it into a mirror !
    13. Small balloons exert higher pressure ?
    14. How does turning this knob control your fridge temperature?
    15. How does sand from Sahara end up in your windshield ?
    16. A note on Vibration and Washing Machines
    17. You cannot drown in Quick Sand!
    18. The great pyramid of Giza has 8 sides not 4!
    19. Why not just build a solar panel around the sun to solve all energy problems?
    20. Major types of engines – giffed

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