Monthly Archives: March 2013

Aerogel

Think about holding a solid block of material in your hand. Whether it is wood, brick, rubber, or metal, you can feel the edges as well as the weight of the object. Now, instead of these common materials, let’s say you’re holding a block of aerogel.

aerogel 1

You will not feel much of anything. The corners of this material seem to fade into the air. It is nearly transparent in some parts, and is literally lighter than air. “Aerogels are the world’s lightest solid materials, composed of up to 99.98% air by volume” (aerogel.org). This ultra low-density class of material has some very astounding characteristics. It’s low density structure allows it to support thousands of times its own weight.

aerogel 3

While it is extremely strong under compression, it is very brittle. It can easily be snapped like a twig. But its amazing properties don’t stop here. Aerogel is one the best insulators in the world to block out intensely high and low temperatures.

aerogel 5 aerogel 4

Furthermore, aerogel is one of the world’s best acoustic barriers and electric insulators. And this is just the general properties of aerogel. Scientists have created aerogel substances out of silica, metal oxides, carbon, and other materials. They have been discovering more and more amazing uses of this type of solid. Because of its superior insulating properties, silica aerogels are used on space equipment, including on the Mars exploration rovers. Metal oxide aerogels, on the other hand, can act as catalysts for chemical transformations and carbon nanotubing and can be made magnetic. And some forms of aerogel have completely different properties than the rest. Cross-linked aerogels are not brittle like most aerogels, but rather have immene strength and flexibility.

Aerogel was first created back in 1931, but the practical uses are just being discovered. Because it is expensive to produce, aerogels have not been integrated into current technology. Once the production process is developed further, this material may provide a cheap and effective solution to many problems. It could become the primary means of insulating houses and buildings. With its incredible absorbing capabilities, it could be used to clean oil spills.

 

 

 

Electricity

In the early 19th century, the history of the world was changed. Michael Faraday discovered electromagnetic induction. From here, electricity evolved to completely dominate many sectors of life in the developed nations of the world.

The laws of electromagnetic induction state voltage is created in a loop of conductive wire when the magnetic field inside of the loop changes. I won’t go into gory detail because the majority of us have learned in physics, will learn this in physics, can use Google, or just don’t care.

But I bring up electromagnetic induction because it is the property that led to the creation of electricity. Magnets are rotated around loops of thick wire to create the current of moving electrons that is electricity. For years, and through today, the main form of electricity production is using a turbine and generator.

Fuel, whether it is coal, natural gas, geothermal, nuclear, etc., is used to create heat. This heat is used create steam from water. The steam, which is pressurized, turns a turbine, which turns the magnets in the generator that cause the magnetic field to change within the loop of wire, creating electricity.

Even some of the newer energy sources rely on the same concept. Wind turbines and hydroelectric plants use the power of the wind and water, respectively, to turn the turbines directly to create electricity.

As I was pondering the future of energy (especially after our sustainability discussion), I wondered why there is such a reliance on this turbine-generator system. Looking into it, I found some very interesting things.

You may have noticed that I left out solar energy in my list of sources earlier. This is because it does not use a turbine. Solar panels contain photo-voltaics. These convert energy directly from sunlight (photons) to electrons – the photons transfer energy to electrons which, with the added energy, can be freed from their material to flow through wires, creating electricity.

Furthermore, I stumbled upon thermocouples, which are called thermoelectric generators (TEG) when discussing electricity. They transfer heat directly into electricity without using turbines. To my surprise, they are not just prototypes or theoretical; TEG are used in satellites that are sent to Jupiter and Saturn – they are too far from the sun to rely on solar power.

I still wonder which of these sources is the most efficient. I assume it is the turbine system because it is most widely used, but I don’t know. In the quest for sustainability, the focus is many times the fuel source. The discussion usually revolves around technology as well. I think it would be interesting, and maybe more beneficial, to change the focus of research. With all of these new methods of creating electricity, could there be way to create electricity without using the usual fuels, which pollute our Earth and deplete our natural resources.

A final random thought: why electricity? It took years and many developments in many different times to discover electricity, to then create electricity (later improved to make efficient), and finally to learn that it can be used to power things, and to take advantage of this power. What if there is something other than electricity that can do the same?

The Doppler Effect

The siren of an ambulance is blaring, you pull over and wait for it to pass, and as you do so you notice something. As the ambulance approaches, the sound of the siren becomes intensified, as expected, but the really interesting phenomena occurs when the ambulance passes you. While intensity changes because of the change in distance between you and the siren, this is not the interesting phenomenon that I am talking about. As the ambulance approaches, a high frequency sound is heard. Just as the ambulance passes, the suddenly frequency drops, and you hear a lower pitch. This is the Doppler Effect.

The Doppler Effect applies to all waves: sound, visible light, radio waves, etc. It is defined as a change in an observed frequency due to relative motion between the source of the wave and the observer. The basic explanation for this is represented using waves generated from the source at even time intervals.doppler

The circles int his picture represent sound waves being emitted at even time intervals. As the police car approaches the man on the right, the wave fronts are closer together because while each wave front is depicted during the with the same time interval between two waves, the car moves during this time interval. This causes the wave fronts on the right to be closer together, which is heard as a higher pitch or frequency. On the left, the wave fronts are spread out and therefore the observed frequency is lower. This is displayed really well by the last animation on this site. Because the wave fronts are pushed together or spread out due to the motion of the car, this phenomenon depends on the relative speed between the source and the observer.

doppler equ

This equation shows how the observed frequency, f ‘, is a function of the original frequency that is emitted, f, the speed of the wave in the given medium, v, the speed of the observer, vo, and the speed of the source, vs. The signs depend on the situation. If the source is moving towards the observer, only v is left on top of the equation, and the sign of the +/- on the bottom of the equation is chosen to be minus. Because the source is moving towards the observer, the observed frequency is higher; subtracting on the bottom gives a lower number which increases the factor by which f is multiplied. The sign is switched if the source moves away. The situation is switched if the observer is moving. The sign on top is a plus if the observer is moving towards the source and negative if moving away; this will correspond to the correct type of frequency shift.

I found it interesting that the Doppler Shift depends on not only the relative speed between the source and the observer, but also depended on which of the two were moving. I found the explanation was actually much more simple than I had expected.

Doppler Effect Derivation

This link is a mathematical representation of two wave fronts, both emitted from source S, with a time interval in between the two occurrences. An equation can be written to relate the two distances traveled, and worked out as follows:

vsnd t = vsT + vsnd(t-T) +λ’

vsnd t = vsT + vsndt – vsndT +λ’

0 = vsT – vsndT +λ’

λ’ = (vsnd – vs)T

where T is the period and T=1/fS

therefore λ’ = (vsnd – vs)/fS

and λ’ = vsnd / fD

so fD = fS vsnd / (vsnd – vs)

This equation represents the source moving towards the detector, D, in the image. To analyze the situation where the detector approaches the source, we imagine time going backwards. The detector can now be seen as the source; the wave fronts are leaving from this moving object (the detector now acting like the source) and converge onto the stationary source which is acting like the detector. In the Doppler Effect equation that was derived above (the last line of the work above), this is represented by switching  fwith fS  and changing vwith vD; this will lead to the other form of the overall Doppler Effect equation that is seen above, where v(the same as vD), is on the top of the equation affecting frequency as opposed to vwhich is on the bottom of the equation when the source is moving.