Category: engineering

An Engineer, Polarized sunglasses and round airplane windows

When you induce stress on an object and see it through your Polaroid sunglass, then you witness these amazing rainbow patterns.


This property of a material where the changes in optical properties of a material is used to determine its stress distribution is known as Photoelasticity.

The simplest way to understand stress distribution in a material is by using a sponge and some wooden planks.

Observe how the lines on the sponge change when one applies the load:

Uniformly Distributed Load


                                  PC:  University of Manchester

Concentrated Load


When a concentrated load is applied, the lines closer to the loading point become radially distorted but the effect of this distortion dies out as moves away. *

If those lines made sense to you, then the lines that you see through your polarized sunglasses are no different.


      Photoelastic visualization of contact stresses on a marble in a C-clamp


In addition, the patterns that you observe are directly proportional to load that you apply. You vary the load, you vary the pattern observed.



Why are airplane windows round?

How does knowing the stress concentration help you at all ? When you are an Engineer, knowing the stress concentration tells you the critical stress points in a structure ( or points of probable easiest failure )


                     Stress concentration in Square v/s Oval windows

As this Real Engineering video goes on to explain when square windows are used in an aircraft, there is a greater accumulation of stress in the edges than the oval windows.

This increased stress, lead to cracks forming near the sharp edges of the window and causing major havoc, which is why all modern aircraft windows are round.

That being said, it is ironical to note that pilots on aircrafts are not supposed to wear Polaroid sunglasses while flying!

( Check out the previous post to know more)

* Saint- Venant’s principle

Why pilots use non polarized sunglasses ?


Polarized lenses are not recommended for use in the aviation

While useful for blocking reflected light from horizontal
surfaces such as water or snow,


polarization can reduce or eliminate the
visibility of instruments that incorporate anti-glare filters.


Polarized lenses may also interfere with visibility through an aircraft
windscreen by enhancing striations in laminated materials (known as photoelasticity)


     Photoelastic visualization of contact stresses on a marble in a C-clamp.


and mask the
sparkle of light that reflects off shiny surfaces such as another
aircraft’s wing or windscreen, which can reduce the time a pilot has to
react in a “see-and-avoid” traffic situation.


*Source:  Polarized v/s non polarized cockpit images

This should have kept you up all night! If you read the previous…

This should have kept you up all night!

If you read the previous post on the Fourier Series, then you might have noticed that this animation was kind of lying to you.

It surely does seem to resemble a square wave but notice that the peaks in red : They are overshooting  and undershooting the maximum and minimum amplitudes.

What on earth is happening here? This goes by the name ‘Gibbs Phenomenon’.

We do not have enough terms

Remember that in Fourier Series you are trying to construct a square wave (which has sharp edges) with smooth and continuous sine and cosine waves.


Fourier series promises us to reconstruct the waveform perfectly ONLY if we provide it with the entire spectrum of frequencies.

But practically we can only work in a finite range of frequencies and when working in a finite domain this overshoot is unavoidable and does not die out.


And if you are an engineer working with a system whose maximum output must not exceed the limit, this can be quite frustrating.

Is there a way out of this ?

In order to get much smoother Fourier series, methods such as Fejér summation or Riesz summation, or sigma-approximation are employed.

Here’s the Fejér summation in action:


                                     Without Fejér summation                              


                                        With Fejér summation

Have a good one!

** Read more about the consequences of Gibbs phenomenon here

The Great pyramid of Giza has 8 sides not 4!!


You may know that a pyramid has 4 faces ( excluding the base ) and the pyramid of Giza has been the popular exemplar for a pyramid.

But, the great pyramid has 8 faces ( excluding the base ), not 4!! 


                                   PC: The History Channel

In his book The Egyptian Pyramids: A Comprehensive, Illustrated Reference, J.P. Lepre wrote:

very unusual feature of the Great Pyramid is a concavity of the core
that makes the monument an eight-sided figure, rather than four-sided
like every other Egyptian pyramid. That is to say, that its four sides
are hollowed in or indented along their central lines, from base to

This concavity divides each of the apparent four sides in half,
creating a very special and unusual eight-sided pyramid; and it is
executed to such an extraordinary degree of precision as to enter the
realm of the uncanny. For, viewed from any ground position or distance,
this concavity is quite invisible to the naked eye.

The hollowing-in can
be noticed only from the air, and only at certain times of the day.
This explains why virtually every available photograph of the Great
Pyramid does not show the hollowing-in phenomenon, and why the concavity
was never discovered until the age of aviation.

It was discovered quite
by accident in 1940, when a British Air Force pilot, P. Groves, was
flying over the pyramid. He happened to notice the concavity and
captured it in the now-famous photograph. [p. 65]


                              Satellite image of the Great Pyramid.


Were the pyramids built this way on purpose or did it turn out this way over time is something that still requires a much deeper investigation.

**  The Great Pyramid of Giza has 8 Side [Video]

Caught in a vortexOne of my friends shared with me this gif of a…

Caught in a vortex

One of my friends shared with me this gif of a butterfly getting caught in the front wing vortex of the car. The purpose of the vortex is to deflect the air flow from the front wing preventing its interaction with the front tire thereby reducing drag.

But how a butterfly got caught in this flow is beyond me. RIP butterfly.

** Check out our mini-series ‘Up up and away’ where we explored the physics of stalls, boundary layers, and F1 cars if this post fascinated you. Happy Thanksgiving!

Meet SAW (or Single Actuator Wave-like robot). A bioinspired…

Meet SAW (or Single Actuator Wave-like robot). A bioinspired robot that can move or swim forward and backward by producing a continuously advancing wave.

Earth’s rotation and Space shuttle launches


Last week we were talking about wind patterns and how they affect flight time. But it is also worth mentioning that Space shuttles are launched almost at all times from West to East to take advantage of the earth’s rotation

How does earth’s rotation affect shuttles ?

Earth is a spherical body rotating with some angular velocity. And as a result of this, the equator is rotating at a higher velocity than the poles. By launching a space shuttle from the equator you are getting a ‘speed boost’.  


This means that if a shuttle is launched from the pole, it has to accelerate from 0 to 17000mph to reach orbital velocity.

But if a shuttle is launched from the equator, it only needs to accelerate from 1025 to 17000mph. (that 1025mph initial velocity is given by the earth free of charge)

This saves valuable amount of fuel required for propulsion


Polar Orbits


Not all rockets are launched from the west to east and the direction is determined by the purpose of its payload.

The satellites that are used for mapping for instance follow a Polar Orbit i.e they move from north to south or vice versa and therefore during launch they cannot take advantage of the earth’s rotation.

Florida or California


Another characteristic of launching satellites is that the launching
stations are generally located near the coast just in
case of failure of the launch, the satellite falls in an uninhabited area.

NASA primarily uses Kennedy Space Center, Florida for east-west launches and Vandenberg Base California for polar orbits for the very same reason. ***


Rocket science is just truly breathtaking.

* How fast are YOU spinning on Earth’s axis right now?

** Also check out about Retrograde motion

*** This statement holds true for most launches.

This is a Dragster BlowoverTop Fuel Dragster racing is the form…

This is a Dragster Blowover

Top Fuel Dragster racing is the form of racing where a vehicle accelerates up to 4g along a mile strip, reaching speeds upto 570 kilometres per hour (335 mph) and finishing the
305 metre (1,000 ft) runs in (3.5-4.0) seconds.


The way that a simple wheelie works is that:

If the torque applied by the engine placed on rear axle is greater than the torque exerted by the vehicle at the center of mass, the front end of the bike/car will rise.


If you don’t have an engine powerful enough to do a wheelie, having some friends to volunteer as sources of torque works too !


Now a blowover is not primarily caused by the immense torque exerted by the engine.

A blowover is the flipping of a car, due to air sweeping underneath it. This creates an aerodynamic lift which blows the car over.


If a vehicle is traveling at 200mph , the vehicle must only be pitched up a 3 degree angle to initiate the blowover.


                                            Wheelie bar

And then came along wheelie bars which completely stopped this from occurring. The wheelie bar ensures that the car does not flip under high torques and speeds.

** Extra:

Moment analysis of a Top Fuel Dragster


Two-phase flows involve more than one state of matter – in…

Two-phase flows involve more than one state of matter – in this case, both gas and liquid phases. Flows like this are common, especially in applications involving heat transfer. In some heat exchangers, bubbles will rise and then slide along an inclined surface, as shown above. The motion of these bubbles is a complicated interplay between the surface, the bubble, and the surrounding fluid. The bubble’s wake, visualized here using schlieren imaging, is unsteady and turbulent. Although the bubble oscillates in its path, the wake spreads even wider, and its turbulence stirs up the liquid nearby, increasing the heat transfer. (Image and research credit: R. O’Reilly Meehan et al., source)

How do zippers work?* How are zippers made ?** Lego zipper

How do zippers work?

* How are zippers made ?

** Lego zipper