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DavidStack

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Blog Entries posted by DavidStack

  1. DavidStack
    There's more to the knowledge I've gained from the Kerbal Space Program. First of all I couldn't get the screen shot to work; I guess the F1 key doesn't like me. And yes, I did just use a semi-colon outside of English class. But another very important thing I've learned through the Kerbal Space Program is how to correctly get a lot of power to your rocket. While I previously thought that either putting one engine at the bottom of stack of fuel tanks (the engine doesn't have enough power to lift up that much weight) or that having layer upon layer upon layer of fuel tanks and engines (the rocket becomes too wobbly and essentially combusts) were good ideas, I soon discovered that two separate layers of fuel tanks and engines, one on top of the other, is a great combination since it makes the rocket not too wide so that it flies straight but also gives the rocket enough power to get off the ground and eventually orbit in space.
  2. DavidStack
    A dear friend of mine and I have recently started playing NCAA Football 12 on his 360 and most of the time I win, thanks to my knowledge of physics. Because I understand the concepts of conservation of momentum, work, and air drag, I very often run the ideal football play - the running back slip screen. For this play, the offensive linemen break their blocks on some of the defensive players who are rushing the quarterback. Lured into the illusion that they can have an easy sack, these linemen and/or linebackers charge towards the quarterback. At this time, the running back breaks his block and turns towards the quarterback for the easy dump pass, like this:

    After that, the linemen that "missed" their blocks before now block for the running back, who has many blockers and open field in front of him. He does not need to worry about the defensive players behind him because of the law conservation of momentum: the defensive players are sprinting in one direction and they need a strong force (which comes from their muscles power) to reverse their momentum to the opposite direction. On the other hand, the running back's blockers are always moving in the right direction, so the do not need this strong force and their momentum aids them in delivering solid blocks. Not only so, but this play works much more consistently than a pass down-field because of the principles of work and drag force. The simple equation for work is force times displacement, so to throw the ball far down the field, the quarterback must do a lot of work. The correct amount of force needed for a far throw is difficult to consistently deliver, making this pass much harder. The drag force on the ball also applies because the ball travels in the air longer for farther passes, so the drag force acts on the ball for a longer period of time, affecting the consistency of the throw. Thus, because of my understanding of mechanics, I can lead a well poised offense to give my Michigan Wolverines the win every time.
  3. DavidStack
    So, we've lasted half the year in Physics, and what better time than now to discuss how I'm feeling about this class?
    Ups:
    1) Physics C and BC Calc go well together. As I learn more in one class, it helps me understand something better in the other class.
    2) It's interesting to learn more real world physics, such as air drag and taking friction into account, instead of learning the mechanics of a perfect world that doesn't exist.
    3) Doing the same topics as last year, like momentum and energy and kinematics, has helped me to gain a better understanding of those concepts.

    Downs:
    1) Rotational mechanics makes energy and pulleys much more complicated. Before, it was very easy to find the kinetic energy of a ball rolling down a hill or the acceleration of an pulley with a massed string (when we were allowed to ignore things we no longer are allowed to ignore), but there are more components now.
    2) I have to study. In Physics B, I could do little to no work prior to taking a test and still do very well, but that is not the case now.
    3) Webassigns are longer and more difficult.

    Even though physics is definitely more challenging this year, I've made it this far with very few bumps and bruises, so the rest of the year can't be too bad (knock on wood). E and M here I come!
    I'd also like to give a shout out to Slim Shady/Mr. Jericho/Mr. Ditty - you've done a fabulous job looking important while Mr. Fullerton teaches, and we're really gonna miss you. Visit soon!
  4. DavidStack
    1) Don't worry about the time, it will just make you work slower.
    2) If Mr. Fullerton says it's going to be on the AP, it's probably going to be on the AP.
    3) Since the AP changes every year, test taking strategies can often come in handy more than trying to hammer in every single thing we ever learned in the entire year.
  5. DavidStack
    Reiterating Charlie's most recent blog post, this independent unit has certainly seemed more difficult conceptually than the previous independent unit. As soon as I thought I understood something in the unit, another curve ball was thrown at me. Luckily, I discovered that Ampere's law and the Bio-Savart law are extremely helpful and applicable in this unit, and the right hand rules and simple force equations (like F=q(v x and F = I(B x L)) are easier this year because of the practice we had with them last year. Thus, knowing those equations and laws should help greatly on the test, as well as being able to apply things from previous units. It is pretty interesting when mechanics, electricity, and magnetism all come together in a problem as centripital force is equal to the force of two charges attracting/repelling each other which is equal to the force due to the magnetic field. Making the connections between the two halves of the year is becoming easier and it is cool to think that famous theories are created by doing what we are doing - making comparisons to two different fields and seeing how they are related. So all in all, while this is a more difficult independent unit, it is certainly fascinating as well.
  6. DavidStack
    So, we all know that everyone in our AP-C Physics class has to be a nerd to be crazy enough to take this class, and i think we could come up with a lot of great nerd costumes. For spring potential energy and conservation of energy, someone could attach a spring to the front of his or her clothing and then run into people and bounce off with equal kinetic energy. Or, for centripetal motion, someone could carry around a rope which he or she hands one end of to random a random person and then runs in a circle around the person, holding the other end of the rope. Or, for the grandest of all, we could have a class atom costume, where a couple people are protons (all blue clothing with a giant "+" on the front) and a couple are neutrons (all gray clothing with a giant "o" on the front) and the rest of the class--hopefully the smaller people--as electrons (all yellow clothing with a giant "-" on the front) running around the cluster of the nucleus. Next Halloween is about to be bumpin'.
  7. DavidStack

    Mind Teaser

    By DavidStack,

    In my computers class we looked up mind teasers on mindcipher.com in order to improve our problem solving abilities, but problem solving is certainly applicable to physics and this question was relatively easy but got your brain working a little bit:
    You need to tell time for 30 seconds but all you have is a non homogenous rope (some parts burn faster than others) that you know burns for 60 seconds and a match. How do you tell time for 30 seconds?

    And if that one is too easy:
    It's said that a number N with 4 digits is a double-square number when it equals the sum of the squares of two numbers: one formed by the first two digits of N, in the order they appear in N and the other formed by the two last digits of N in the order they appear in N.For example, 1233 is a double-square number since 1233 = 12^2 + 33^2. Find another double-square number.

    Enjoy!
  8. DavidStack

    Triple Jumping

    By DavidStack,

    Although I had to quit indoor track because of an ankle injury, I did learn a lot about the precision of triple jumping form from my coach. Previously, I had run my approach with my chest not perpendicular to the ground but slightly more forward and my knees did not move very high. With this form, my momentum (which points perpendicular from my chest) was pointed into the ground, preventing me from jumping as far as possible. My knees also needed tweaking, since a lot of the power from jumping comes from the knee drive. Because my knees moved little as I approached my jump, it was hard to suddenly rip my knee up when I took off, due to the conservation of momentum (it takes an external force to change the direction of my momentum, but if my momentum was already directed up and forward, that force would not be necessary). With a continued knee rise throughout my approach, I could develop a more fluid and powerful jump. While these adjustments to the approach slightly decreased my speed, they vastly improved my control and jumping power, greatly lengthening the distance I could jump.
    This world class jumper displays this approach form, leading him to a record breaking jump:




  9. DavidStack

    Stunts!

    By DavidStack,

    If you have ever watched Hot Rod, one of my favorite movies, then you understand the joy/hilarity of poorly thought out stunts. My brother and I have always enjoyed puting ourselves in harms way of the purpose of an awesome video, but I've discovered that we are much more willing to do painful stunts if we are landing into water instead of on solid ground. Most recently, we went to some pier that was 10 or so feet off of the ground and attempted backflips on our bikes off of a ramp into the water. I don't think either of us would even imagine attempting such a thing if we were to land on the ground. But why? It has to do with molecular structure, a topic concentrated in Chemistry but still very important in Physics, as molecular structure impacts things like air drag and electrical forces. So, solids have a stiffer molecular structure than liquids because they move less, and likewise liquids are stiffer than gasses because they move less. Due to the cusion-like complection of water, it is safer to land in than landing on dirt. Professional stuntmen in movies often land in air-water mixtures instead of actual water because the air-water mixture is much less stiff, breaking the fall of the stuntman more than water would. This all relates back to impulse, as the less stiff structures provide a longer time of impact, reducing the force felt on the person.
  10. DavidStack

    Ping Pong

    By DavidStack,

    Ping Pong has always been one of my favorite leisure time activities, and after embarrassing a good friend of mine yesterday with my ping pong skills, the physics of the sport came to mind, especially the physics of my favorite shot: the top spin shot. Arguably the most effective shot, the top spin increases your accuracy with more powerful shots, and is very difficult to return. But why?

    The picture above shows how the spin of the ball forces the air below the ball to take a longer path, while the air going over the top of the ball has a shorter path, thus moving faster relative to the ball. Because of this difference in air speed, there is a downward force on the ball, causing the dip of the ball soon after it is hit. With this dip, the ball falls faster than a non spinning ball, allowing the player to hit the ball with more force and still have it drop on the other side of the table, giving the player more accuracy. Then, the forward spin of the ball couples with the forward direction of the ball upon impact of the table, increasing the speed of the ball and making it difficult to return. This very interesting physics of air flow is used in designing air planes, rockets, and many other inventions.
  11. DavidStack

    Momentum and Tennis

    By DavidStack,

    No doubt, the weakest part of my tennis game is returning hard serves. I often try to hit powerful shots, so i take a large backswing. But, when returning a serve, the ball already has a high velocity, so a large backswing is not needed to hit the ball back with a high velocity. Actually, a small swing is much more effective and accurate. This is because of the principle of momentum. When hitting a serve, a large swing is necessary to give the ball a high speed because the ball, right before contact, has a momentum very close to zero. So, a large force is needed to produce a large momentum. But, when the ball is traveling to the opponent with this large momentum, the opponent does not need to generate a large momentum in return, they only need to redirect the momentum. Thus, a large backswing is not necessary; the opponent just needs to hit the ball with a short and quick swing. If you watch professional tennis players, you will notice that they rerturn really fast serves with fast returns with a small and quick swing, as they have learned of the physics of tennis and know to simply redirect the momentum, not try to create new momentum. Once you understand the physics of tennis, you'll be looking like this guy.

  12. DavidStack

    Car Crash!

    By DavidStack,

    As we dive into impulse and momentum in this independent physics unit, I am reminded of my only car "crash" I've ever experienced, if you can even call it that. When I was backing up in a small parking lot several months ago, the back of my car bumped into a small pole that I didn't see, jerking my car to a stop. Due to the minimum speed my car was moving at (5 mph or 2.24 m/s), my car was not damaged at all. So I was interested in finding out what speed it would have been damaged. Given that the car accelerates from 0 m/s to the collision speed in 1 second, its acceleration will equal the collision speed. The force of the collision is measured by F = ma, and with a mass of 1000 kg (close to the mass of my Toyota Corolla), F = 1000 * a. A 1000 kg car can withstand an impulse of about 1000 N*s without damage, so with a collision time of .2 seconds (for the car, not the driver), and the equation J = F * change in time, J = 1000 * a * .2. Thus, 1000 = 200 * a, meaning that the car can top out at an acceleration of 5 m/s^2, or a collision speed of 5 m/s (11.2 mph), without damaging the car if the car starts from rest.
  13. DavidStack
    I have always failed at writing down 50 equations in 4 minutes, both last year and this year, and I was never really sure why because I do know a good deal of equations. But as I think about it, I usually try to think of every little equation - getting me flustered and slowing me down - instead of focusing on the general equations that can help me figure out other equations. So, here's a simplified equation dump of equations that can lead you to most any equation we've learned in mechanics.
    F = ma
    K = .5mv^2
    U = mgh
    p = mv
    J = F(delta)t = (delta)p
    W = Fx = (delta)K
    P = W/t
    U(s) = .5kx^2
    F = -kx
    F(g) = (GMm)/r^2
    F(f) = (mew)F(n)
    T = 2(pi)(m/k)^(1/2) -> for springs
    T = 2(pi)(l/g)^(1/2) -> for pendulum
    T = 1/f
    F© = (mv^2)/r
    I = mr^2
    I = I(cm) + Mx^2
    v = v(0) + at
    x = x(0) + v(0)t + .5at^2
    v^2 = v(0)^2 + 2a(x-x(0))

    And for rotational mechanics, the analogs are:
    torque = F
    theta = x
    omega = v
    alpha = a
    L = p
    I = m

    This does not cover every single equation, but it hits the most important ones and can centralize your equation focus while preparing for the midterm.
  14. DavidStack
    As my last blog post of the quarter, I think the only reasonable thing to do is get sentimental (at least as sentimental as you can in a physics blog post) and think of the ups and downs of this quarter. This quarter was mostly independent units, which was good in the fact that it helped prepare us for college but also made me realize that I need to change a lot of my study habits - or lack there of. I also have discovered that E&M comes a lot less naturally than mechanics did, so studying for the E&M AP could take a good deal of time. And even though I thought I could stay up to date on my blog posts after the first quarter, I failed that once again, so hopefully the fourth quarter can finally be the quarter of success. Thus, I have learned that more work on physics outside of class would be benefitial, as well as staying more focused during work time in class. Fourth quarter here I come!
  15. DavidStack
    Many people do not enjoy plane rides because of the uncomfortable feeling of their ears popping as the plane rises. This has to do with air pressure, a concept that is not really covered in AP-C Physics but we did deal with last year and is certainly important in understanding the general physics around us. As the airplane increases in altitude, the air becomes less dense (since less air is being pushed down by gravity), leading to a decrease in air pressure. Because of this, the air trapped in your inner ear will cause your eardrums to push outward, causing a discomfort. To compensate for this, your body naturally allows some air from your inner ear to escape through the Eustachian tubes, two small channels that connect the inner ears to the throat, creating the "pop" of your ears. You likely had no interest in this, or you were already aware of why your ears pop, but thanks for reading anyways!
  16. DavidStack

    Catapults

    By DavidStack,

    Depressingly, I followed the whizzing ball as it flew past the 50, the 60, the 70, and even the 80 yard mark. Our costly (both with time and money) trebuchet could not compare to the spring loaded demon of a catapult that bested our yardage by 44. But, this project certainly did improve my engineering knowledge. Comparing my trebuchet to another very similar one that flung the softball farther, I saw that with a stiffer structure, we could have had more success. If we had used screws instead of nails, and secured the pole that our level arm swung on with bolts instead of duct tape, we could have supported more counter weight and had a more fluid, straight, and speedy projectile. Also, the record-tying trebuchet showed me that a bigger catapult is not necessarily better, as that trebuchet was less than half the size of mine but shot the ball so much farther because of the very powerful springs and bungee cords. So, I can say that our catapult did fairly well, I enjoyed the creativity and problem solving that the project required, and I am better prepared for projects in the future.

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