# pavelow

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1. ## 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 as a Particle and a Wave

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. ## Rail Guns

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 Trains

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 in Your Home

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. ## Why is Exploring the Ocean so Hard?

"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. ## Electromagnets

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. ## Magnets and Their Properties

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.

12. ## Catching up on Sleep

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. ## Crash Test...Not So Dummies

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. ## Pressure's Effect on State Changes

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. ## Nuclear Reactions

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:
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