Pantograph and Trains

Pantograph is a very interesting device that you may find on the roof of electric trains, trams or electric buses.

And the primary purpose that it serves is to collect power from the overhead power line to run the motors of the train without losing contact at higher speeds.

The train takes the current
from the over head line and the current flows to the tracks
which are earthed at regular intervals via the axle brush on the train.

This completes the circuit.

                                               Source

The overhead lines are kept in tension and dropper wires are placed at multiple locations to ensure that the contact wire does not bend under its own weight.

And since any two objects that rub against each other, constant frictional contact would wear them out, the Pantograph and the contact wires have a sliding contact.

This results in less wear for both the Pantograph and the contact wires resulting in lesser maintenance.

Graphite conducts electricity extremely well while also working great as a lubricant due to it’s self-lubricating properties and therefore most contact strips on the Pantographs are made up of Graphite.

It’s a very simple apparatus with an extremely pivotal role and that’s what makes  the Pantograph special. Have a great day!

* Trolley pole

** Third Rail

*** Arcing is a serious problem when we are dealing with any high voltage lines. in bullet trains which operate under higher voltages, the Pantographs are always forced to be in contact with the contact wires through a dynamic lever-spring mechanism. (Source)

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The Touch Screen

fuckyeahphysica:

One cozy evening, I gazed a lazy look to the surrounding. From the looking glass of a Lazy individual everything looks dull.

But once my vision tuned in on the Smart Phone, it struck me that I had no idea how this thing works but yet have been using it constantly for years. Time to disparage the boredom !

This is an account of the bewitching touch screen world. All Aboard!

The Resistive Touch Screen

If you have used a mobile phone in the distant past that involves you pressing down hard on the screen, then there is a great possibility you have used a Resistive touch screen.

Some examples are the Nokia N800, Nokia N97, HTC Tattoo, Samsung Jet or the Nintendo DS.

How does it work?

This is the traditional form of a touch screen and its working is rather blunt. There are two conductive sheets present that are separated by spacers.

When you press your hand against the screen , the top layer gets pressed and
makes contact with the bottom layer. This completes an electrical
circuit.

The act of pressing reduces the resistance between the two conductive plates. (because you are reducing the distance between these two conductive plates and resistance is dependent on the length of the medium)

The voltage established as a result of this change in resistance is measured and the coordinates of the point of contact are determined.

The harder you press, the more the change in resistance.

This is one of the frustrating things about this type of touch screen.

Resistive touchscreen require slight pressure
in order to register the touch, and are not always as quick to respond.

But they are used in many low-budget mobile phones like the Freedom 251, which is a touch screen phone for $3.75.

The Capacitive Touch Screen

                                                Source Video

Now over to the touch screen that we are most accustomed with: the capacitive type.

Capacitive touch screens are constructed from materials like copper or indium tin oxide that store electrical charges in an electrostatic grid of tiny wires, each smaller than a human hair

When a finger hits the screen a tiny electrical charge is transferred to
the finger to complete the circuit, creating a voltage drop on that
point of the screen.

Due to the transfer of some amount of charge from the screen to your
body. this change will be noted by the monitor placed below the screen
and the exact location of your touch is noted.

Note:

Plastic does not allow charges to flow through. Ergo, if you try to use it whilst wearing gloves or anything plastic / non-conductive materials, the screen will not respond to your touch!

But leather or other conductive materials on the other hand will allow charges to pass through, which is why they work well with any smart phone.

Hope you guys enjoyed this post . Have a good day!

* Some of these facts may not apply to Rugged phones like the CAT S61 or its variants.

Source: fuckyeahphysica

The exotic moves of the human eye

It is always a humbling experience to compare our progress in technology with what nature has been doing for decades on end.

1-2 –> Iris in camera vs human eye

3-4 –> Iris mechanism in camera vs human eye

5-6 –> Accommodation of the eye

Have a good one!

* Pupil dilation video

* Eye contraction video

* Understanding the functioning of the Eye

* Bio-mimicry and eyes

Aircraft operations in Infrared

Taxing

                                                 Source

Take-off

                                                Source

Landing

                                                  Source

Reverse Thrust

                                                  Source

Deicing

                                                    Source

For more interesting aircraft action in IR check out these videos:

* Aircraft inspections in Infrared

** Takeoff, landing and more – as seen from cockpit using IR camera

*** Landing with and without FLIR (Forward Looking Infrared Radar) 

If unit vectors always scared you for some reason, this neat little trick  from The story of i by Paul Nahin involving complex numbers is bound to be a solace.

It allows you find the tangential and radial components of acceleration through simple differentiation. How about that! 

Have a good one!

** r = r(t),  θ =  θ(t)

In 1941, Swiss engineer George de Mestral noticed after a
hunting trip that burrs from burdock plants stuck to his pants and his
dog’s fur. 

He took the seed and looked at them through a microscope to find that this seed
attaches to animal fur via the hooks on its surface to improve
distribution.

                               Source: All of Nature on Blogspot

These hooks would latch onto anything loop-shaped, such as the fibers in his pants and his dog’s tangled fur. This inspired him to come up with the ‘Velcro’.

Velcro is a bio-mimicry of this burrs with small flexible hooks attached on its surface to attach to fluffy surfaces.

Although it goes by the name Velcro the generic name is a  hook-and-loop fastener)  

And depending on the load that needs to be held there are different types of hooks that are available:

The sound that the velcro makes when you rip it apart is oddly satisfying. It is made when the loops are ripped apart from the hooks.

It was always in my head that the hooks or the loops would break whenever you would rip it apart. But turns out, they are extremely flexible.

                                                Source

For a long time I believed that this was the end of the story and that’s how far we had gone. But recently when I was trying to mount a board to the wall, I came across the 3M dual lock fasteners.

These use a mushroom shaped hook on both the sides to snap together in place.

                                                  Source

And evidently it turns out the mushroom fastener design were inspired from dragonflies who used it for stability during mating (check source video above for more).

This is great, but since this is made of plastic this surely would fail at higher temperatures. You need something robust to handle higher temperatures, and this is where the Metaklett comes into the picture:

A square metre of this fastener, called Metaklett (made of steel), is capable of supporting 35 tonnes at temperatures up to 800 ºC,  (Video)

There is something exotic in the blend of nature and technology that is manifested in the Velcro, I just cannot put my hand on what it is.

Have a great day!

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.

              Source

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 do pilots use non polarized sunglasses ?

Polarized lenses are not recommended for use in the aviation
environment.

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.

– FAA

*Source:  Polarized v/s non polarized cockpit images

People are awesome & Math is beauty

The white circles albeit traveling in a straight line across the circle exhibit a more collective circular behavior.

Here’s a much more real world scenario which follows similar guidelines:

If you notice, the motion of all the workers individually are also periodic in nature, but each of their motion is slightly out of phase leading to this beautiful symmetric behavior that constitutes this gif.

Truly mesmerizing!

The mathematical sciences exhibit order, symmetry and limitations; and these are the greatest forms of the beautiful

– Aristotle

** Radial engines too BTW:

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