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

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) 

Fluorescent lamp with and without phosphor coating

When an electric current is passed through the mercury vapor that is present inside the Fluorescent lamp, it excites it and produces short-wave ultraviolet light (LEFT).

But a phosphor coating on the inside of the lamp makes it glow white (RIGHT). The type of phosphor coating dictates the color of lamp

                                                Source

For example, in the tube above
a coating of red phosphor is applied the right, followed by a band of green, a
band of blue, then with all three mixed together to produce white light,
and finally on the left an uncoated region showing the mercury
discharge inside.

And that’s how we get Fluorescent lamps of different colors!

* More on the working of Fluorescent lamps

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!

How do you place a satellite in orbit?

With all the media frenzy about Spacex over the days we received a few requests asking us to explain how satellites are launched into orbit.

We shall do so through a thought experiment proposed by Isaac Newton when he was trying to understand how the moon was orbiting the earth.

Newton’s cannonball

Just imagine standing on top of a really tall mountain with some cannonballs and a cannon.

We will start firing these cannon balls with different speeds by constantly increasing the amount of firepowder that we add and observing the response.

(a) Speed of cannonball < 7300 m/s

(b) Speed of cannonball ~7300 m/s —-> Circular orbit

( c) Speed of cannonball ~8000 m/s —-> Elliptical orbit

(d) Speed of cannonball ~11200 m/s —-> Parabolic trajectory

(e) Speed of cannonball – Crazy

Gunpowders are not that powerful !

In the real world instead of using gun powder, we use much more sophisticated and powerful
solid rocket fuels which will take the satellite from earth and put it
in orbit.

But once the satellite once put in orbit just keeps falling into orbit.

This applies to the ISS as well: “ISS is always falling; Falling into orbit.”

Although this is not by any means a comprehensive post on this topic, but hopefully this gives you a sense of the physics of how satellites are placed in orbit.

Have a good one!

** TRY IT OUT – Newton’s Cannon 

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

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:

One
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
peak.

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]