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  2. It would be interesting to see how this glass would protect against a grenade. Where would all the tiny particles momentum go (because momentum must be conserved).
  3. Simpsons Physics 2: Springfield Gorge

    In an earlier episode of what came to be an instant classic, Homer Simpson accidentally attempts to jump over the "Springfield Gorge" (most likely the Simpson's version of the Grand Canyon). Anyway, while this scene is extremely funny, there some inconsistencies to laws of physics. In this blog I am going to point out a few. First off, when Homer first goes off into the air, he stays at the apex of his motion for about 3-4 seconds while only having a horizontal velocity. In fact, it almost seems as if Homer's vertical velocity seems to oscillate up and down. Of course, any physics student will tell you that this is incorrect, force there should be a net force of the force of gravity acting on Homer, and therefore he should have been accelerating downward (not in vertical equilibrium). Furthermore, when we get a wide-shot of Homer, once he realizes he is not going to make the jump, the acceleration due to gravity acting on him seems to increase exponentially; it certainly was not a constant acceleration and while this makes for hilarious television, it does not meet real life physical standards. Lastly, Homer actually falls down the cliff twice, and the force of the gorge and rocks acting on his body would surely be enough to kill him, but of course he is Homer Simpson, and when he wants to, he gets to decide the laws of physics.
  4. Better to Run or Walk in the Rain?

    A very popular and interesting YouTube channel I watch is minute physics, where a guy does short videos on different concepts of physics. One video I have recently watched is about whether it is better to run in the rain or to walk in the rain. In other words, which choice will get you least wet. For one thing, the amount of rain that falls on your head is constant, as when you move out of the way of one rain drop, you move into the way of another rain drop. However, if you are the more horizontal distance that you travel, the more rain will hit you from the side. Therefore, the faster you move, the wetter you become. However, when you are trying to get from one point to the next, the amount of rain you run into will be constant (like a snowplow plowing a volume of snow, the speed it plows it does not change the amount). Therefore the answer is simple: Run. The less time spent in the rain, the better. Credit to minutephysics (at YouTube.com)
  5. Diet Coke explodes when you drop mentos in it, most people have seen it, if not done it themselves, but why? Well, there are a lot of parts to answering this question. First of all, why Diet Coke? Well, Diet Coke generally has slightly more carbonation than regular Coke, which plays into the next part. The bubbles are drawn to the small indentations in the metros, as they search for a way to escape the liquid, which causes a foam, which will create pressure within the bottle eventually causing the explosion. Because mentors are made of many layers, each layer has lots of microscopic bumps that provide a lot of surface area for the carbon dioxide bubbles to grab on to. Because of the increased carbonation in Diet Coke, and the effect of the mentors on that carbonatin the build up in pressure as a result causes the explosion that we all know.
  6. Yesterday
  7. We use microphones all over the place, and most people have one or more on them at any point in time. Most work on a fairly simple concept, using 2 plates. One of them is much thinner than the other, and acts as the diaphragm, the part that moves as a result of sound. The other one is thicker, and works to make the 2 plates into a capacitor. The sound waves change the distance between the two plates slightly, and therefore changes the capacitance of the system. These changes in capacitance are measured and turned into sound via speakers. Speakers work on a principal that is similar but opposite. Instead of measuring, the diaphragm is moved by varying electric fields in a coil around a magnet. By charging the coil with the right amount of electricity at the right time, it allows for sound waves that mimic what the microphone recorded to be produced. This is a very analog system, meaning it isn't controlled by a system of 1's and 0's being interpreted by a processor, but rather the strength of the charge resulting from sound into the mic. Obviously this can be converted back and forth from digital, but the speaker will always be a very analog type of technology.
  8. Each pixel has 3 color filters in front of the backlight, electricity applied to the liquid determines it's opacity, and therefore how much of light goes through the color filter. Essentially, the liquid crystal can be controlled as to how much light is let through, and the 3 different color filters allow the pixel to assume a large array of different colors. Calculators use LCD displays, but without a backlight or any color filters, and only have 2 states for the crystal, fully opaque or fully transparent.
  9. A new type of software development that is being used to create realistic looking water without having large processing times is based off of approximating almost everything. The basic principal is to use a bunch of small spheres, and calculate how they would react in whatever situation, say water pouring out of a pipe. This would look like a large amount of balls rolling out of a pipe, but the real magic happens in the approximations that are used. The software uses how the balls move to judge how the water would move, and make it look like water by making the balls invisible, and adding water where the balls are, and if one gets separated it simulates how surface tension would be broken, and the water would form a droplet. This type of approximation allows the software to render realistic looking water at a resource cost that is far less than a typical simulation. By adjusting certain parameters, the viscosity and surface tension of the apparent fluid can be changed, allowing for this to be used to render all different types of fluids, not only water. This can also be adjusted to model smoke and fog, although with a largely different set of rules on the physics of each particle. Here's an example from NVIDIA's tech demo before: And then after the approximations:
  10. My only question: How does the screen realign the liquid crystal such that it can actually produce the proper color?
  11. WoP #15: Hyperion Moon Shot

    In the Borderlands series, specifically Borderlands 2 and Borderlands: The Pre-Sequel, corporate villain Handsome Jack and the company of Hyperion use a device on their moon base/corporate HQ to launch supplies and killer robots down to the planet of Pandora and its moon, Elpis. But just what is said device? During the beginning of Borderlands: The Pre-Sequel, you get the luxury of being shot out of the moonshot cannon in an emergency evacuation. Fun! But, in the chamber for the moonshot, there is no visible propulsion device: no explosive charge or rocket to launch it. So what does propel the moonshots? Simply put, the moonshot cannon acts as a railgun. So, how does a railgun work? By connecting a projectile between two long rods, and running a current through the rods, it's possible to create an induced magnetic field which launches said projectile without the need for a conventional propulsion mechanism.
  12. We spend many hours every day looking at some sort of display, whether it be attached to a computer, phone, TV, or maybe even a car. These displays work on a relatively simple concept of using liquid crystals that change the color of the light that is provided by the backlight, which is usually white. This tech has replaced the old CRT (cathode ray tube) technology that shot electrons at a screen over and over scanning across to form the image. The next innovation in display tech is hopefully something like what Iron Man has in his suit, a type of transparent display. The current tech used would work somewhat as a transparent display, but the colors would be affected by whatever light is behind them, as no light is being produced by the display, only altered. This is where OLED (organic light emitting diodes) come into play, as they are one of the newest type of display technology, and they create their own light. This means that the colors you see are being produced pixel by pixel, rather than a white light being altered pixel by pixel. This also allows for better contrast, as each individual pixel can turn off, making the display capable of having true black rather than a sort of blocked backlight. This tech also allows for flexible and more varieties of displays, which are already being used in some TV's today.
  13. This is pretty interesting. So, being speakers operate based on electric signals and magnetism, is the pickup sort of like a reverse speaker, where the sound moves a magnet, causing electric signals, instead of the other way around?
  14. Many have seen the Back to the Future trilogy, in which Marty McFly and Doc Brown use a modified DeLorean to travel through time. According to Doc Brown, the machine requires "1.21 Jigawatts" of power (confirmed by the directors to simply be a mispronunciation of Gigawatts) to power the flux capacitor, which enables time travel. This is achieved by bringing the DeLorean up to a speed of 88 mph, roughly 39.34 m/s. Using this information, I will do what any sane person would do: calculate the mass of the DeLorean. Before I can calculate the mass, there are a few missing pieces I need to know or assume. First, the coefficient of friction between the tires and the road. Considering that roads at the time were mostly made of concrete, it's safe to use the coefficient of friction for rubber on concrete, which will be somewhere between 0.6 and 0.85. Being the car is in motion, and the wheels are rotating, the static coefficient of friction should be used, so I'll take the higher value of .85. Second, I'm going to assume that air resistance is negligible in this case, and that all work done on the DeLorean comes from the force of friction, which is used to accelerate the car forwards. Finally, I'm going to assume that the DeLorean moves with a constant acceleration, such that the average velocity of the car is equal to half the final velocity, or 19.17 m/s. With that done, I can work backwards from the beginning to determine the DeLorean's mass. First of all, being power can be calculated using the equation P=F•v, and the net force on the car and velocity of the car are in the same direction, Net Force = P/v = 1.21 x 109 W / 19.17 m/s = 6.31 x 107 N. Being friction is the only force acting to accelerate the car, this is also the force of friction. Now, being the force of friction = µ(Force normal) = µmg, the mass of the DeLorean = Ffriction / (µg) = 6.31 x 107 N / (0.85 x 9.81 m/s) = 7.57 x 106 kg. Looking up the actual value for the mass (yes, you can find it), it's about 1230 kg, a large discrepancy. While the assumptions made above, especially concerning air resistance, don't help the numbers, the fact of the matter is that Doc Brown never fully explained how the DeLorean worked, so it's almost impossible to calculate a realistic number for its mass. Besides, would you really want him to? If so, be prepared to sit through a full movie dedicated simply to explaining the science behind it before even beginning the actual trilogy.
  15. What a guitar amp does is pretty self-explanitory, it's even in the name. It amplifies the sound of an electric guitar. Although an acoustic and electric guitar operate fundamentally differently, similar principles apply to both, strings vibrate at a specific frequency, the sound waves then resonate though the wood and air, creating sound, however, electric guitars have their own method of amplifying the sound, an amplifier. Electric guitars all feature some kind of pickups, which pick up the sound from the strings, and send it to a quarter inch audio jack on the guitar. That jack, with some assistance from a quarter inch cable, can then in turn be plugged into an amplifier. Many common guitar amps feature both the amplifier as well as a speaker within a single enclosure, however many higher end amplifiers will require a speaker cabinet, as they do not have an integrated speaker. The amplifier itself amplifies the electronic signal, that is picked up by the pickups and transmitted via the quarter inch cable, and then sent to the speaker and played back much louder than the initial sound created by the guitar itself.
  16. Hi Gio. APlusPhysics is just a single person, me, so that's pretty easy to answer. They are on my to-do list, but are at best a month or two away. Note that most of this material is covered to at least some depth in the "Honors" physics video series. Hope that helps! -Dan
  17. The bigger question is, would we be dumb enough to blow up the only planet we can currently live on?
  18. Interesting. So, do shock waves in water act similarly to sound waves, then?
  19. WoP #13: Falling with Style

    In the previous post, I referenced a quote from Toy Story, said by Woody after Buzz is first introduced, in response to Buzz's stunt around Andy's room. If you haven't seen the first Toy Story (which I don't know why you wouldn't have by now) turn away now before I spoil a minor part of the end of the movie. You know who you are. Alright, here it goes... At the end of the movie, Woody and Buzz are trying to get back to Andy, and have to chase a moving van on RC. In the process, Buzz lights a firecracker that was attached to his back, sending him and Woody into the air to eventually fly down into Andy's car. Simple, right? Well it is, until you realize that Buzz and Woody, even if you refer to what they did as gliding, shouldn't have been able to stay aloft. Disney's artistic physics license implies that Buzz's "wings" were enough to keep both him and Woody aloft, due to air resistance. While the pressure differential above and below the wings due to moving air would cause that in real life, the shape of Buzz's wings don't allow that. Because Buzz's wings are flat, the amount of air pushing up on the wings will equal the amount of air pushing down on the wings. If you don't believe this, just look at any airplane. The curvature of the wings is what allows air resistance to keep the plane aloft in the first place. In short, Buzz's flight was impossible, and would have been even more difficult while carrying Woody.
  20. WoP #12: Flying Dogs

    Let me start this by saying that the title is a bit of a misnomer. Dogs cannot fly, no matter how fast of a running start they can get. While a hyper dog may be able to leap over several people, an ottoman, and half a couch with a single bound, they have no way to force air down such that they stay aloft. In the words of Tom Hanks, "It's not flying, it's falling with style." Having said that, dogs actually can do a ton of cool things. Namely, standing on their two rear legs. The canine body is most certainly not designed for them to put their full weight on two legs, yet they are quite clearly capable of such a feat, as many internet videos can testify to. As such, how is this possible? While their center of mass isn't usually directly above their point of contact with the ground, meaning gravity would pull them down, dogs get around this with one simple trick: jumping. Almost every video where dogs are on their hind legs has them jumping on them to stand up. What does this do? Quite simply, with the way that they jump, they cause a torque on their bodies which cancels out the effect of gravity, allowing them to stay up in such an unnatural manner.
  21. The Helmet

    It is better to not get hit in the head but sometimes it just ends up that way. Hockey helmets are designed like most helmets with the ability to absorb most of the energy from impact. The thing that I believe separates a hockey helmet from a standard football helmet is the fact that the top of the line hockey helmet rotates a little around your head without jerking your head in the initial impact. (I don't Know enough about football equipment to speak on behalf of the equipment) However, most injuries that occur to the head are caused from the initial jerk of the head when the brain remains still for a moment while the head moves. As this movement happens it yanks on blood vessels and nerves causing strain on the head and if bad enough an actual brain bleed or a concussion. This is why I wear the top of the line helmet now because previously having a really bad concussion and now I must wear it to prevent future ones. With this helmet no one is safe from every hit but with the ability to rotate a little around your head it gives you a slight edge over other helmets.
  22. Sounds like a wicked concussion. I'll stick to the ones from hockey
  23. Underwater Explosion

    When an explosive goes off under water the shock wave carries a lot further than it would if it were on land and in the air. This is cool because water has a higher density than air so this mean that it is harder to move or has higher inertia. And we know that inertia is a measure of how restive something is to acceleration. This means that after the explosion goes off the shock wave from that will carry further through the water with smaller deceleration. From this we know that this shock wave will be carried without losing speed and keeping it's high kinetic energy. As a result of this if you are anywhere near an explosion in the water you will be feeling most of the energy from the explosion. This energy from the explosion depending on the size could have enough energy to shatter every bone in your body. I would suggest getting out of the water if you were in this situation but, chances are you would be to late.
  24. This past semester I took "History of Warfare", a half-year elective that took an in-depth look at all major US wars since WWI. On the last day of the class, we shifted focus to the homefront and talked about mental injuries veterans sustain and how they try and cope after war. One thing that really shocked me was the existence of a fairly recently discovered injury called Traumatic Brain Injury (TBI). What surprised me even more was the way in which this injury was sustained. Essentially, the supersonic winds created by explosions cause the brain to rock inside the skull over a time period of about 3 milliseconds. What is amazing (and very concerning) is the fact that these winds can impact anyone in the blast radius of 1 foot to up to 1 mile. The brain even moves so fast that your body doesn't even know its happening... and because of this it is an injury that over 200,000 living veterans suffer through every day. The symptoms can be compared to CTE in football players and leave veterans feeling "punch drunk" just like the worlds most famous boxers. The physics come into play when the blast wind hits the body. First off, the shock of the wind is transmitted to the body as a wave of energy and any surface (like a skull or helmet) can reflect the wave, meaning it can impact the brain 3-5 times per explosion. In WWI, when the symptoms were first being documented, leading doctors thought the kinetic energy of the blast traveled up the spinal column and into the brain. Now, there a are theories that go so far as to say shock waves of kinetic energy can reach the brain through the bloodstream. Although the injury is very serious, it is interesting from a physics perspective to think about the energy transfer happening between those billions of particles through the bloodstream, spinal cord or skull. P.S.- Anybody with a free period should see if they could get into this class for the new semester. Its an eye-opening class that was definitely a great choice of an elective.
  25. That's a really cool idea to keep kids safe playing a sport they love.
  26. Its crazy how this bullet resistant glass is able to absorb so much energy.
  27. It's funny to think that flipping a bottle is considered a talent now.
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