Dude, Bullets Are Literally Made To Shatter On Impact. It's To Prevent Over-penetration. Bullets Frequently

How does sand from Sahara end up in your windshield ?

TBH cleaning your car is a rather mundane task. But when you fill your head with some interesting physics the task actually gets rather pretty interesting. Here’s some good for thought on such an occasion :

The dust on your windshield might actually be from the Sahara desert

To understand how, lets start with some simple physics.

The stacked ball drop

You basically take couple of balls, align them up and drop them to the ground. The ball at the top reaches the most highest due to the subsequent transfer of energy from the other balls.

                                    Source Video : Physics Girl

Here is an exaggerated but amazing slow motion of the same energy transfer with a water balloon. Notice how the transfer of energy takes place between the water balloon and the tennis ball.

                                     Source Video : Slow Mo Lab

Sandstorms in the desert

Sandstorms/ Dust storms as you might be aware, are pretty common in the desert. . Dust storms arise when a gust front or other strong wind blows loose sand and dirt from a dry surface.

And this can cause something phenomenal to happen:

If the wind speed is sufficient then larger sand particles can propel finer ones high into the atmosphere. ( just like the stacked ball )

Then these fine particles are caught in the global wind pattern and are transported across the globe until they fall down to the earth as rain.

How cool is that ! Have a great day!

* Tracking saharan dust in 3D - NASA video

** All the World’s a Stage … for Dust - NASA article

** Wiki on Saltation

The Amateur Cloud Watching Handbook (#1)

Cloud watching is one of the most pleasurable activities on the planet. You don’t need any fancy equipments or spend money to experience it. Just find a spot to rest and witness the show that nature has to offer.

It is the most breathtaking experiences one can ever resonate with.

Fellow cloud watchers from the past have identified 3 primarily forms of clouds that seems to be consistent everywhere and have named it based on its structure, for the sake of convenience.

Cirrus

Cirrus in Latin means Tendril or hair. The clouds that are like long slithers in the sky, are called by this name.

Cumulus

Cumulus in Latin means Heap or pile. They just look heaps of white floaty objects in the sky.

Stratus

Status in Latin means Layer or sheet. They occur when startas of clouds stack on top of each other.

Clouds are constantly merging and doing all sorts of crazy stuff and they rarely maintain the same shape as you might have already observed

To account for this, dude named Howard brilliantly came up with a elegant nomenclature.

If a Cirrus type cloud after some time transforms into a Stratus type, it is known as Cirrostratus.

If a Cirrus type cloud after some time transforms into a Cumulus type, it is known as Cirrocumulus

If a Stratus type cloud after some time transforms into a Cumulus type, it is known as Stratocumulus

And so on, you get the idea right. By merely observing the transformation pattern of the clouds, you can tell its name.

This helps in setting up something of a standard to express in words what you behold, although it will never exactly be the same that someone else has in mind.

Note on Language

Language is our means of expression. Sometimes we stick with the conventions that had been established by pioneers. Now, that doesn’t need to be the easiest way.

For instance QWERTY keyboard is not the best keyboard to type in, but we still follow it as a convention.

Fortunately, cloud watching conventions are so much intuitive than many others out there!

Have a good day.

PC:  Ted-ed PiccoloNamek,  Nissim Angdembay

( Part -2 coming out soon )

More Than You Ever Wanted to Know About Mechanical Engineering, Part 33: Stress Concentrations With Fluctuating Stresses

There’s one last complication to consider with fluctuating stresses. When we looked at the case of fully reversed stresses (that is, σ_m = 0, σ_a ≠ 0) we found a fatigue stress concentration factor based on the stress concentration factor for a static situation.

With a fluctuating stress, the situation is a little different. Since the mean stress is non-zero, the part is always under some kind of load. We can consider the effects of this constant mean stress separately from the effects of the momentary alternating stress and assign them a separate fatigue stress concentration factor, which we’ll call K_fm.

Let’s think about what’s actually physically happening to a part being subjected to a fluctuating stress. Let’s say we’re dealing with a plate with a slot in it subjected to fluctuating tension.

There’s obviously a large stress concentration at the slot that we’ll have to take into account.

There’s three different scenarios which can occur here. The first is that the maximum stress the plate sees (the largest value of combined mean and alternating stress, taking stress concentrations into account) never approaches the yield strength of the material. The plate just stretches and contracts elastically. This isn’t really any different from our previous situation with fatigue stress concentration factors - we can use the K_f factor we got earlier here.

But suppose the yield strength is exceeded. What happens then? If the maximum stress is greater than the yield strength, then the plate must deform plastically at that point of maximum stress - the slot must widen. If the slot is wider, then the stress concentration is relieved - there’s more room for movement before the geometry stops you. If other words, the fatigue stress concentration factor is lessened.

If it’s just your maximum stress that exceeds the yield strength but your minimum stress is still below it, this localized yielding will be one-sided - you’ll get a slot that’s widened on one side, but you’ll still have some overall mean stress. If this is the case, you base your stress concentration factor on the relationship of the mean and alternating stresses to the yield strength.

If both your minimum and maximum stresses exceed the yield strength of the material, you get a situation where you’ve widened the slot as far as you can without actually breaking the part on both sides and you’re experiencing a stress of magnitude equal to the yield strength at either extreme of the fluctuation. Since you now have a fluctuation with equal and opposite extremes, your mean stress is zero - the mean fatigue stress concentration factor is zero. The scenario is now one of fully reversed loading and the mean stress drops right out of it.

Dissecting Iron Man Suit - An Engineering Analysis

Structural, energy, and thermal analysis of Iron Man Suits specifically Mark I to Mark XLVI which have the following capabilities in common: external armor, supersonic flight, hovering, weaponry, and decoy flares.

1. STRUCTURAL ANALYSIS 

Wear Resistant and Shock Absorbent Exoskeleton  The physical protective value of exoskeleton is its ability to resist any penetrative loads as well as any shock loads. However, the whole thickness of exoskeleton panels should not be too hard because it will pass on the external impact load into the suit’s internal hardware, or even the human body inside it. All of this can be achieved by combining more than one materials; a hard material on the outside and the soft material on the inside

Hard Outer Layer for Penetrative Loads The materials needed for the exoskeleton’s outer layer should be hard and tactile. Titanium Alloy would be an ideal choice. Fiber glass has good tensile strength but not good shear strength, while titanium has both .Titanium Alloy is not only much stronger, but is also lighter than steel, which will provide more fluidity of movement compared to any heavy material counterparts.

Ductile Inner Layer for Shock Loads There should be a soft inner linings behind titanium panels to serve as shock absorbent. Sorbothane is a material that is extremely soft and has the ability to convert shock loads into heat transfer at a molecular level. It is a proprietary, visco-elastic polymer. Visco-elastic means that a material exhibits properties of both liquids (viscous solutions) and solids (elastic materials).

Sorbothane is a thermoset, polyether-based, polyurethane material. Sorbothane combines shock absorption, good memory, vibration isolation and vibration damping characteristics. In addition, Sorbothane is a very effective acoustic damper and absorber. Even if one drops an egg from the top of a building into a bed of sorbothane, this remarkable material is soft enough to cushion the impact and would not allow the egg to break.

This technique of having a hard material on the outside and the soft material on the inside is not new. It has been used for centuries in Japan for making samurai swords. The hardness of its outer layer give the swords its cutting edge and penetrative power, and its ductility allows it to absorb shock loads when it strikes or struck. 

2. ENERGY ANALYSIS : Hovering Capability

Hovering using thrusters (aka repulsors) requires tremendous amount of energy, particularly when the suit is used for a long duration. Energy usage for hovering is dependent upon the hovering methods

Magnetic Levitation requires no energy at all, but is limited to the presence of magnetic field.

Ducted and Open Propellers (helicopter blades). Several human powered helicopters have been made overtime that have achieved flight. It has been experimentally recorded that a 78 kg person in a 58 kg copter requires only 1.1 kW to climb using helicopter blades, and only 60 Watts to maintain altitude.

Jet Thrust is the least energy-efficient method. Because thrust-to-weight ratio needs to be greater than 1 to achieve lift-off, a Jet-pack requires over 1KN of thrust force, depending on the weight of the jet and the person. If wings are attached to the jet-pack, horizontal flight can be achieved with thrust to weight ratio lower than 1, thus improving the duration of the flight and its range.There have been jet-packs made in the past, most iconic display of it was in 1994 Olympics opening ceremony. The fuel used in the jet-pack was mostly hydrogen peroxide. It provides thrust at low temperature compared to other fuels. However, it has low energy density of 810 Wh/kg, giving the jet-packs up to only 30 seconds of flight-time. Jet’s flight time is limited even by using energy-rich fossil fuel. Yves Rossy (aka Jet Man) has successfully used kerosene oil in his flight, but the thruster jets have to be pushed away from the body for safety. His suit allows only several minutes of flight. In addition, if a heavier suit (greater than 25 kg) is used, hydraulics are needed, which would require additional energy and slow down mobility. The Iron Monger suit was an example of hydraulic-driven mobility suit.

3. POWER SOURCE

Tony Stark manages the suit’s energy requirements, including thermal management and artificial intelligence system, through the fictional arc reactor. The reactor is able to provides almost limitless clean energy despite being a very small device. In real life, the only thing that has an energy density comparable to the arc reactor, and would meet all the energy requirements of the suit would be nuclear power. Uranium (fission) energy density is 80.620.000 MJ/kg. However, nuclear power is not suitable to be harnessed in a manned suit, since it generates a tremendous amount of heat.

A more practical solution would be a battery energy-storage. If lithium batteries are used on propeller blades, minutes-long flight time can be achieved. Furthermore, these batteries can readily power suit’s electrical devices / electronics requirements. Lithium ion battery has energy density of 150 Wh/kg (0.5 MJ/kg). Fossil fuel, on the other hand, have a much higher energy density than batteries, but would require a clunky generator to power the suit’s electrical requirements.

Lithium sulfur batteries have 5 times more energy density compared to lithium ion batteries. Lithium sulfur packs had already powered the longest unmanned flight for more than 30 hours. Unless we discover something like an arc-reactor, lithium sulfur batteries could be just the thing to power up the suit. The downside is, it requires hours of charging for just minutes of usage.

There is an alternative option, though not a ‘reactor’ proper. A compact and high-output generator (standard car alternators crank out 50-70 amps at 12 volts for years, and some can go as high as 150 amps) could be spun by a small and strong output electric motor (all alternators have to do is spin). That motor can be powered by a high density battery like used for electric bikes in the 1500w to 2500w range at 20 something volts. This would power a strong and small motor at 3500 to 4000 rpm for hours. That’s more than enough to create power for a number of systems, if they’re built to take advantage of the amperage. And with new constructions of carbon arrays coming out every day, one or more of those could bring a meaningful electric output increase in an otherwise standard generator, even above what we have in cars now.

4. THERMAL MANAGEMENT 

The suit cannot be hermetically sealed. Human body heat evaporates water from the skin. Therefore, air ventilation is a must to remove them. It is also needed to maintain a good supply of oxygen. So, there must be a structure inside the exoskeleton that allows air flow. This would prevent any internal condensation to settle and will also remove buildup of body heat. The layer of sorbothene would act both as a thermal and an electrical insulator. This means that extreme external temperature would not be transferred to the inner layer. The suit would not get too hot or too cold from the outer environment. There should be small fans to draw and pull air from the ambient in controlled amount, and should be able to exchange hot air. With the technology available today, the thermal management of the suit is easily manageable. There are also solid state devices such as thermal pads and thermoelectric generators. Thermoelectric generators can surfaces hot or cold depending on the polarity of the electric current and thus can be an integral component of the suit for controlling the internal temperature.

Source (x)

Keep reading

Crows Are So Scarily Clever They Can Judge Weight Using a Technique We've Only Seen in Humans

When we look at the way an object moves, humans are able to use this context to infer weight - whether it is light or heavy.

Crows and ravens are pretty well known for their incredible smarts. In this experiment, psychologists sought to determine how well New Caledonian crows can infer weight.

Science Fact Friday: Bird lungs! Just like every other part of a bird, they’re weird.

This gif shows the path of a single breath, but the circuit holds 2 breaths at a time. So when the bird inhales, the just-inhaled breath goes through Inhalation 1 while the previous breath goes through Inhalation 2. Rinse, repeat. Thus, the lungs are constantly receiving oxygen - in mammals, our oxygen content dips slightly between inhalations because there’s no fresh air coming in. We also don’t empty 100% of our lung volume so some air is “stale” even during an inhalation.

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Transcript below the break.

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A portal to another universe ?

That my dear friends is a CT scan machine. Stripped off all the body parts, you can see clearly see what goes on inside.

A computerized tomography (CT) or computerized axial tomography (CAT) scan combines data from several X-rays to produce a detailed image of structures inside the body.

                                            CT scan of Brain

Pretty cool, don’t you think ?

Extras

Difference between MRI and CT scan

Why dont you spin the patient instead ? - Awesome reddit thread

Better quality gifs : here

Source Video: Micheal Jonnson

Are Cloaking Devices Coming? Metalens-Shaped Light May Lead The Way

“The biggest challenge facing a real-life cloak has been the incorporation of a large variety of wavelengths, as the cloak’s material must vary from point-to-point to bend (and then unbend) the light by the proper amount. Based on the materials discovered so far, we haven’t yet managed to penetrate the visible light portion of the spectrum with a cloak. This new advance in metalenses, however, seems to indicate that if you can do it for a single, narrow wavelength, you can apply this nanofin technology to extend the wavelength covered tremendously. This first application to achromatic lenses covered nearly the full visible-light spectrum (from 470 to 670 nm), and fusing this with advances in metamaterials would make visible-light cloaking devices a reality.”

What would it take to have a true cloaking device? You’d need some way to bend the light coming from all across the electromagnetic spectrum around your cloaked object, and have it propagate off in the same direction once it moved past you. To an outside observer, it would simply seem like the cloaked object wasn’t there, and they’d only view the world in front of and behind them. Even with the recent advances that have been made in metamaterials, we have not yet been able to realize this dream in three dimensions, covering the entire electromagnetic spectrum, and from all directions. But a new advance in metalens technology might get you the full electromagnetic spectrum after all, as they appear to have solved the problem of chromatic aberration with a light, small, and inexpensive solution. If we can combine these two technologies, metalenses and metamaterials, we just might realize the dream of a true invisibility cloak.

Whether you’re a Star Trek or Harry Potter fan, the ability to turn yourself invisible would be Earth-shattering. Come see how transformation optics might transform the world!

Just imagine a world full of beautiful stained glass windows which also generate electricity…

[Oxford Photovoltaics]

Blackest is the new black: Scientists have developed a material so dark that you can't see it...

Puritans, Goths, avant-garde artists, hell-raising poets and fashion icon Coco Chanel all saw something special in it. Now black, that most enigmatic of colours, has become even darker and more mysterious.

A British company has produced a “strange, alien” material so black that it absorbs all but 0.035 per cent of visual light, setting a new world record. To stare at the “super black” coating made of carbon nanotubes – each 10,000 times thinner than a human hair – is an odd experience. It is so dark that the human eye cannot understand what it is seeing. Shapes and contours are lost, leaving nothing but an apparent abyss.