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Everything posted by pavelow

  1. pavelow

    Two-way mirrors

    "I'll take mirrors for $200, Alex." "This type of mirror is a mirror on one side and a window on the other." "What is a one way mirror?" "You got it."
  2. Light is subject to a quantum theory called wave-particle duality. This theory proposes that matter exhibits both properties of a particle and properties of a wave. The experiment that shows light's wave-like properties is the double slit experiment. when light was shone through two slits close together, and a screen was placed behind the slits, the impact pattern didn't look the way one would expect a particle impact pattern to look like. After going though the slits, the light diffracted, creating a wave diffraction pattern on the screen, showing light's wave-like properties. Light's particle properties are shown in another experiment. Light is passed through "absorber" planes, which don't affect waves. however, when the light passed through the absorbers, the wave after going through the absorber was considerably weaker. This confirmed that light has some particle like properties. Light is neither particle nor wave and yet exhibits properties of both, which can be experimentally observed.
  3. A military application of electromagnetic force is the rail gun. A rail gun is like a regular gun in the sense that it fires a projectile out of a barrel, but it has some major differences. A regular gunpowder gun uses a projectile with a firing pin, which is hit by the gun, pressurizing gunpowder, resulting in an explosion which propels the projectile forward. This is a bit inefficient however, because a lot of recoil occurs in the gun because of conservation of momentum, and a lot of excess heat is produced. The rail gun propels the projectile differently. Instead of using gunpowder to propel the projectile forward, the gun uses electromagnets along the barrel to accelerate the projectile to high speeds. this results in a less sudden recoil and a more efficient way to shoot a projectile, and as the technology improves, rail guns will eventually replace large guns for military use.
  4. Magnetic Levitation (Maglev) trains are one of the ways electromagnets are used every day. Maglev trains carry passengers at speeds of 310 mph. The trains are able to reach such high speeds without falling apart partially because of their sturdy design but also because of their propulsion system. The trains are held up by magnetic forces when they approach higher speeds.the lack of physical contact with rails reduces friction to only that of air resistance, allowing the train to be more stable at high speeds. The main issue keeping maglev trains from becoming more common is economical, not technological. Once the remaining problems are solved, these trains will be a better solution for high speed travel than the current bullet trains in use all over the world.
  5. The electrical grid is wired in parallel. Why? The benefit of having your home wired in parallel rather than in series is having a uniform voltage rather than a uniform current. Because your home is wired in parallel, manufacturers of electrical products can set a specific resistance and know the expected current because of ohm's law V=IR, rearranged to I=V/R. The danger of having everything wired in parallel is that increasing the amount of resistors in the circuit decreases the equivalent resistance of the entire circuit. This can lead to a dangerous amount of current travelling though the wires in your house. However, there are safeguards preventing a dangerous amount of current from damaging the products in your home. The circuit breaker exists as the weakest part of the circuit that is your home. This ensures that, in the case of a dangerous amount of current, the circuit breaker flips first, so any products plugged into your outlets are kept safe. Wiring in parallel makes developing electrical consumer products easy and protecting against the dangers of parallel circuits is done by the circuit breaker.
  6. "The ocean covers 71 percent of the Earth's surface and contains 97 percent of the planet's water, yet more than 95 percent of the underwater world remains unexplored." Source: http://www.noaa.gov/ocean.html Many obstacles exist keeping widespread ocean exploration from becoming something not extremely difficult. One obstacle is the pressure under water. "The deeper you go under the sea, the greater the pressure of the water pushing down on you. For every 33 feet (10.06 meters) you go down, the pressure increases by 14.5 psi (1 bar)." Source: http://oceanservice.noaa.gov/facts/pressure.html To efficiently explore the ocean depths, the tremendous water pressure must be dealt with in order to keep electrical instruments working. Additionally, the electrical instruments would also have to be waterproofed. The deeper into the ocean you travel, the darker it becomes. A vast majority of the ocean is pitch black and receives no sunlight. In the early 1500s, scientists were already looking into space, but no one could look much farther than a few dozen feet deep into the ocean. Because a large amount of the equipment needed to explore the oceans have been invented fairly recently, deep sea exploration hasn't been established like other fields of science. The harsh foreign environment of the deep sea and engineering challenges that come with it have made it difficult to explore the worlds oceans.
  7. An electromagnet is created when an electric current produces a magnetic field. Electromagnets have multiple applications and are a popular application of magnets. Electromagnets are often used in large metal scrapyards where large amounts of metals need to be distributed quickly and efficiently. A crane with an electromagnet on its arm is perfect for this task because the crane operator can induce a current to magnetize the electromagnet and pick up metal, and then cut the current when he wants to release the metal from the arm. Scientists often use electromagnets for experiments because the electromagnet can be carefully calibrated in ways a natural magnet cannot, allowing the scientists to collect more accurate experimental data, allowing them a better understanding of their field.
  8. Substances are magnetized when their electrons spin in the same direction. What this does is it creates charge differences in a substance. Magnets have north and south poles. These poles dictate the direction in which the magnetic field flows both inside and outside of a magnet. On the outside, field lines flow north to south; inside they flow south to north. Interestingly enough, magnets will always have both a north and a south pole. This can be observed if a magnet is cut in half. Since the poles are the result of the flow of field lines, and the field lines always form loops, there cannot be magnetic monopoles. In other words, there can't be a north pole without a south pole, and vice versa. The magnetic field created by magnets can be utilized to exert forces on other objects. A common application of the magnet is the electromagnet.
  9. There are two often used ways of avoiding RADAR (RAdio Detection And Ranging): Stealth and Jamming. My previous blog post covered stealth. This one will cover jamming. World War Two era planes weren't equipped with stealth technology to avoid radar, because it didn't exist yet. The air forces of the world had to figure out ways to avoid radar, and thus they figured out how to jam radar. World War Two era bombers were easily picked up by radar, so to confuse the towers, the planes released aluminum chaff. From the tower's point of view, all the signals from the chaff looked the same as the signals looked from a squadron of bombers. by jamming the tower with false signals, the airplane escaped without being tracked by the tower. Modern jammers work differently, but have the same purpose. modern radar jammers spam the radar source with false signals on the same frequency as the airplanes flying in the range of the radar. The towers still pick up the planes, but they can't distinguish the fake and real signals.
  10. There are two often used ways of avoiding RADAR (RAdio Detection And Ranging): Stealth and Jamming. This blog post will cover stealth. Radar can be rendered useless or less useful if the radio waves sent out by radio towers never return to the towers themselves. Airplanes today are equipped with more than one way to hide from radar. One way planes can avoid sending radio waves back to towers is by only allowing radio waves to reflect at one angle. The B2 bomber, as shown in the picture, was engineered to be as flat as possible, this causes radar waves to bounce off the plane as if it were a flat surface, and the waves never return to the tower they came from. Another way planes avoid sending radio waves back to towers is by using a stealth coating. Special versions of the F35 fighter jet are painted with a special stealth paint. When radio waves hit the surface of one of these planes, the paint traps the waves and absorbs a large amount of the energy from them. As a result, if radio waves do make it back to the tower of origin, they make it harder for the tower to distinguish the plane from something natural, like a bird, or even the environment itself.
  11. Radar is used by militaries and civilians of the world for object detection. Radar works when a tower shoots a "beam" of radio waves in a direction. If an object is in this "beam" of radio waves, the waves will bounce back to the tower. The owner of the radar tower receives two very important types of data from the use of radar: Distance and velocity. Distance between the radar tower and object is determined by the time it takes the radio waves to return to the tower after they are initially shot. The radio waves travel at light speed. Therefore, it's pretty easy to determine the distance. Take light speed, multiply by the time for the round trip, and you get the distance. there is one twist, however. The total distance must be divided by two because the radio wave made a round trip, going to the object and back. The velocity of the object in the radar beam can be found using the Doppler effect. If the object is moving away from the tower, the frequency of the returning radio waves would drop. The opposite is also true. If the object is moving towards the tower, the frequency of the returning radio waves would go up. The extent to which the radio waves are shifted helps pinpoint the objects velocity.
  12. Every teenager has stayed up late, woken up early, regretted their decision, end then slept extra long the next night. Can a person really catch up on sleep? Numerous studies have been conducted on the subject, and what is the prevailing hypothesis is that there are two systems dealing with sleep, a circadian process and a sleep homeostatic process. The circadian process is a rhythm of sleepiness and alertness over a twenty four hour period. This clock is related to the amount of light received by the eyes and can change when stimulus to the eyes is removed. This cycle is controlled by the suprachiasmatic nucleus in the hypothalamus in the brain. This region of the brain is affected by light and stimulus to the eyes, and it is what causes the circadian process. the interaction of this part of the brain results in changes in hormone levels in the body, promoting either sleepiness or alertness. The sleep homeostatic process is basically a pressure that builds up during the day that promotes sleep. the pressure dissipates during sleep. Being awake for days can build this process up and cause a difference in brain wave patterns when sleep finally comes. However, brain patterns return to normal after only a night or two of sleep, meaning that a lack of sleep happening as a shock isn't known to have lasting effects yet. Chronic sleep restriction and sleeping disorders are much different. Getting less sleep than is necessary on a regular basis can cause negative effects to take much longer to wear off and some effects may not be completely reversible. The problem with studying the effects of chronic sleep restriction is that it is difficult to find willing participants for studies and difficult to produce reliable studies because of lifestyle changes caused by sleep restriction. The physics of all this lies in the fact that all of these effects are caused by electrical and chemical reactions in the brain and body. Also, this was caused by physics. Something as simple as the amount of light entering the eyes can affect the sleep cycles of millions of people. It is important to get a full night's sleep every night, but one night every blue moon won't make a difference in your life. Chronic sleep restriction is the thing that can cause serious problems to the brain, body, and lifestyle. I'm going to bed.
  13. When cars get into a collision, why does it seem like half the car gets turned into debris? The answer is simple, conservation of momentum. In elastic collisions, like car crashes, the projectiles have a lot of momentum. If a head on collision occurred where the cars stayed perfectly rigid, the occupants would have a huge change in momentum. This used to happen before modern safety regulations. Modern cars are designed to "give", absorbing a large amount of momentum and keeping the occupants from experiencing the same change in momentum, saving lives and livelihoods in the process. It is a lot better to lose more of your car than losing more of your body. Enjoy: http://www.youtube.com/watch?v=-nyfRwMQ-Tk
  14. Melting/Freezing points and Boiling/Condensing points aren't just based on temperature; pressure is also involved. This fact can be observed by having a weighted wire go through a block of ice, as witnessed in this video. As shown in the video, pressure is also a major factor in determining the melting point of ice. On a molecular level, the molecules under the wire get increased kinetic energy, causing them to become liquid. once the wire passes through that part of the block of ice, the molecules lose the excess energy and refreeze. The melting/refreezing phenomenon also happens when ice skaters glide on ice. The weight of the person on the skate causes a large force to be exerted on a small amount of ice, melting it, meaning that ice skaters actually skate on water. Once the skater glides over the spot, the the pressure is no longer there, and the water refreezes. Other effects of pressure on state changes of molecules is the effect of high altitude on boiling points. Places like Denver, Colorado which have lower air pressure than places nearer to sea level cause water to boil at lower than normal temperatures, resulting in a need for adjustments in cooking techniques. Differences in pressure as well as temperature have an effect on state changes of particles.
  15. There are two types of nuclear reactions that are very prevalent in today's society: fission and fusion. What are these reactions and how are they used? Nuclear fission is a reaction where a molecule splits into smaller molecules and excess subatomic particles, and releases energy. This type of reaction happens in nuclear bombs and in nuclear power plants. In nuclear bombs, this reaction is set off by a neutron hitting a nucleus, making it unstable and causing fission. In a bomb, this happens in the vicinity of an amount of a particle, called critical mass, where the reaction becomes a chain reaction, causing an explosion. In a power plant, the same reaction occurs, but below critical mass, so the power plant doesn't explode. Instead of the reactions energy causing an explosion, it heats water, which turns into steam and turns turbines, providing power to municipalities. Power plants also have safeguards to slow down a fission reaction in case it becomes too fast. Example: Nuclear fusion is a reaction where two molecules are put together which creates a bigger molecule and excess subatomic particles and releases energy. Nuclear fusion happens on a large scale on the surface of stars, and fusion bombs have been detonated. Fusion bombs operate on many of the same principles as fission bombs, such as needing critical mass to become a chain reaction. Interestingly enough, modern fusion bombs need an initial fission reaction to get enough energy to sustain a fusion reaction for and explosion. The power producing applications of fusion energy are the next frontier of nuclear energy. The current challenge is inducing a safe fusion reaction and producing more energy than is used in initializing the reaction. This is the first step in being able to harness fusion as a power source, and once fusion becomes a viable energy source, the supply of energy becomes extremely large due to the abundance of molecules to use as fuel. Example:
  16. The calculation for escape velocity is a pretty simple conservation of energy problem. K at infinity =.5mv2 = 0 because v at infinity = 0 U at infinity = GMm/r = 0 at infinity because r = infinity K=0 U=0 K=U .5mv2 = GMm/r From there it's simple algebra, and escape velocity is ve = sqrt(2GM/r) This equation's applications are seen in the exploration of space. Spacecraft need to reach escape velocity in order to not eventually crash back into the earth's surface. Some satellites are orbiting earth at just above escape velocity, meaning that they are actually spiraling away from the planet. On the other hand, some satellites are orbiting just below escape velocity, meaning that they will eventually fall into the atmosphere and burn up. However, some of these satellites have on-board rockets which can change their trajectory, allowing for more stable orbits and longer lifetimes. The Voyager 1 spacecraft used its escape velocity to leave the solar system and explore what lies beyond. NASA's Curiosity mission required the spacecraft to reach near escape velocity (although I'm sure the actual spacecraft reached a higher speed) to make it to Mars. As humans explore more of the space that surrounds the planet, escape velocity and its applications will become even more important.
  17. This blog was inspired by this fact: The New York City water supply system leaks at a rate of up to 36 million US gallons (140,000 m^3) per day. Source: http://www.nytimes.com/2008/11/23/nyregion/23tunnel.html?pagewanted=2&_r=0 Our water is extensively purified, and is completely safe to drink, but how can it be safe if some of the biggest supply pipes have holes all over? Besides the full -on sanitation of the water, one part of the solution is that our water supply contains some residual chlorine and other chemicals that stop bacteria growth from occurring in tap water. Any pipe leaks/breaks that occur in supply lines that can actually affect water quality can be isolated and the water diverted until a replacement segment is installed. also, the pipes are pressurized to a level where nothing could get into the system through a hole because of the pressure difference. This is visualized by seeing water leak OUT of a pipe, and not seeing things go in. By the way, tap water is safer than bottled water and is subject to stricter regulations in many different tests.
  18. Is it just me or does it get quieter outside when a couple of inches of snow are falling? Actually, the answer is a combination of both. First of all, during a big snowfall, there are likely to be less people and other noise making devices outside, so there is less initial sound hitting they eardrums, without regard to any effect the snow has on sound waves. What if the amount of noise made is the same before a snowfall and during/after? Sound waves are absorbed by porous and insulating materials. Freshly fallen snow has plenty of air pockets for sound waves to get trapped in. Regularly, sounds bounce off of hard surfaces like the ground before they reach the ear, so when the snow insulates these sounds, the angles from which sounds reach the ear are greatly reduced. The temperature during snowfall compared to a warm clear day is also a factor. Lower temperatures slow down sound waves, and sound waves, like other types of waves, refract when they change speed. During the winter, when the ground is cold, and the air is warmer, like during a clear winter day, sound waves refract down when hitting the lower colder air, making more opportunities for sound reflection. During snowfall, the air is relatively as cold/colder than the ground, causing the opposite effect, leaving less opportunities for sound reflection, and sound get carried into the atmosphere. Enjoy the quiet winter days/nights!
  19. What is Pavel time? Pavel time is the time right before a deadline when actual work gets done. How does this relate to physics? It relates specifically to Albert Einstein's theory of relativity. Part of the theory of relativity states that measurements of various quantities are relative to the velocities of observers. In particular, space and time can dilate. So, in real life, as an object approaches the speed of light, it gets squished and time slows down for the object. How does this relate to Pavel time? In my theory of relativity, as more work gets done more quickly, time slows down and allows me to finish whatever assignment I have before the deadline.
  20. Walking is just controlled falling. Don't believe me? Take a step. The human body has its center of mass high up off the ground, so it requires a continuously acting balance system. When you take a single step, you shift your weight forward in such a way that if you didn't have a balancing system, you would fall flat on your face. At the last second, you swing a leg forward and catch yourself, regaining your balance. Taking a walk is just repeating the same motion over and over again. The reason walking is not thought of very often throughout the day is because it is intuitive. It is learned and perfected early on in life, so many humans don't pay much attention to it. Learning to walk on two legs was a major achievement for the human species, and it helped free the hands to create tools and the civilization we live in today, all because we learned to fall and catch ourselves, and then again and again.
  21. The Nimitz class aircraft carriers currently in service for the US Navy weigh anywhere from 102,000 to 106,000 metric tons. If these gigantic ships weigh so much, why don't they sink? The way a ship floats is not only dependent on its weight. Even though the ship is extemely heavy, it displaces an amount of water which weighs the same amount as the ship. If more of the ship goes under, the weight of the water it would displace would be more than its own weight. This phenomenon causes the water to exert a buoyant force, counteracting the weight of the ship and allowing it to float.
  22. Torque is the tendency of force to rotate something around an axis. Torque helps you turn a doorknob, it makes a car's tires spin, it basically helps a force act in a circle. Applications of torque equations can help solve real world problems. Locations for supports for bridges can be determined by examining the effects of the torque vehicles would cause on a bridge. An engineer looking to efficiently maximize the potential for producing torque in an engine would choose electrical or diesel power over gasoline power to use the fuel effectively. People who would like to easily compare weights without a scale can easily use torque properties to their advantage, specifically with a balance. Putting a weight at each end of a beam and sliding it over a fulcrum until it balances can help determine relative weights of objects by comparing the lengths of sides of the balance. For example, Person A and Person B are on opposite ends of a log, and the log is balanced. The leg extending to Person A is twice as long as the one extending to Person B. because torque is the length of the arm multiplied by the weight of the object, it can be determined that, because the torques balance, Person B has twice the weight of Person A.
  23. Veritasium, a channel on YouTube, posted a series of videos showing an experiment where a bullets are shot into blocks, where one time, the bullet is shot into the center of the block, while another time, the bullet is shot off-center. The first video can be watched here: And the second here: The explanation for the result of the experiment has to do with momentum. While the second block has more energy, it has the same momentum as before, because linear and angular momentum are independent of one another. Because kinetic energy is not conserved in inelastic collisions, the systems can have different kinetic energies while maintaining the same momentum. Explanation video here: Also, shameless plug for his channel. Subscribe. the video was made with help from RIT.
  24. What? Gravity is weak? Then how am I not floating right now? This has to be a joke. It's not. Gravity is one of the four fundamental forces in our universe. The others are electromagnetic, strong nuclear, and weak nuclear forces. Gravity is the oddball in this group. It is also preventing the completion of the unification equation. While the other forces, besides E-M, have relatively short ranges, gravity does not. Gravity has infinite range, and has a bigger effect over range than other forces. Gravity is pulling the Milky Way and Andromeda galaxies together at this very moment. Gravity pulls everything together due to its range and the size of the objects being moved, but it pales in strength to the other forces. When put on the same scale as all the other forces, the force of gravity is an afterthought. At the same levels, E-M forces are magnitudes stronger than gravity. Strong and weak nuclear forces affect individual particles much more than gravity does. For example, the magnitude of E-M force between two hydrogen molecules is an undecillion times stronger than gravity. Why? Science hasn't really given a definitive answer, but we do know that the universe as we know it wouldn't exist without this weak force, because neither would we.
  25. In our body, we often consciously use our skeletal muscles. Our nervous system sends an electrical signal to our muscles which affects proteins which cause our muscle to contract. Electrical energy is transmitted which begins a process of chemical energy being converted to mechanical energy. Some smooth muscles behave like skeletal muscles, while others have contractions which are regularly and methodically induced by specific cells. The actions of these cells keep systems such as the digestive system working continuously without conscious thought. The heart, the cardiac muscle, is controlled the same way as the smooth muscle. The cardiac muscle pumps blood through the body, using mechanical energy to bring oxygen to cells where it can facilitate more chemical reactions.

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