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DavidStack

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  1. 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.
  2. 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!
  3. DavidStack

    Bottle Rocket

    By DavidStack,

    To add to the benefits of the Kerbal space program listed in the previous post, it helped us with the bottle rocket mostly in terms of simplicity. Instead of trying to make a giant rocket with parachutes or other complicated things, we decided to go with a simple rocket because we learned the importance of aerodynamics and weight balance through the Kerbal space program. My group realized that all we really needed was the two liter bottle, fins, a nose cone, and some weight on the top of the rocket in order to help it fly straight and keep the center of mass towards the top of the rocket, while the drag force was towards the bottom of the rocket. Even though our rocket wasn't flashy or put together incredibly precisely, it had the basic components to fly for over 5 seconds, which I consider to be a success.
  4. 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.
  5. 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.
  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

    CYO Swag

    By DavidStack,

    As I perpare myself mentally, physically, and spiritually for the upcoming CYO basketball season, I can't help but think of the physics that partner with a fluid and successful basketball shot. Players that have perfected their basketball shot, like Ray Allen, have found a combination of enough leg bend, a straight-armed follow through, and an effective wrist flick. With these three key components, the ball travels with arc and backspin in a projectile motion, sailing through the hoop. The potential energy developed through the bend of the legs is stored in the leg muscles (which act much like springs), which is then transfered through the arm to the ball and converted into kinetic energy, giving the ball the energy to travel to the hoop. Basketball shots that have arc are much more effective than flat shots because the ball moves less in the horizontal plane in the time it takes the ball to travel through the hoop, so the ball has less of a chance of hitting the rim and bouncing out. Also, the backspin creates a softer bounce of the rim, giving the ball a greater chance of bouncing into the hoop off of the rim. So, through my knowledge of physics, I can focus on getting the power in my basketball shot from my legs instead of my upper body, and making sure I have an effective amount of arc and backspin.
  8. 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!
  9. DavidStack

    Einstein's Hair

    By DavidStack,

    Although Albert Einstein's mess of hair was most likely due to the fact that he rarely slept well because of the equations constantly rattling through his brain and that he really didn't care what he looked like since he was too busy making history, electricity also plays into effect.


    Due to the likely rolling around that Einstein did at night, his hair felt a lot of friction from his pillow case and the sheets on the bed. This frictional force led to the passing of electrons from the sheets to his hair, and since like charges repel each other, the electron build up in his hair led to his hairs repelling each other and standing up on end. And with a known charge of electrons, the repelling force between his strands of hair could actually be calculated with the equation F = kqq/r^2. Someone needed to get that man a comb!
  10. DavidStack

    Feeding the 5000

    By DavidStack,

    In the famous Bible story of feeding the 5000, Jesus and his 12 disciples feed 5000 men with 5 loaves of bread and 2 fish. But, the 5000 only counts the men, and since these people have been following Jesus for over 2 days, it can be assumed that they are with their families. On average, we'll say that each man has a wife and two kids, speaking that some of the men weren't married and some of the men had much larger families. That means that this story is actually the feeding of the 20000.
    First, let's look at how much bread and fish would be needed to feed these people. According to Mark 6:42, the people "ate and were satisfied." These people hadn't eaten for 2 days as they've been following Jesus, so to eat and be satisfied, each person would need at least 2 fish and a loaf of bread. There needed to be 40000 fish and 20000 loaves of bread, meaning that Jesus multiplied the amount of fish by 20000 and the amount of bread by 4000, and that doesn't even include the extra 12 basket-fulls of bread that the disciples picked up afterwards. That's crazy!
    We can also see how long it would take to pass the bread around. The passage states that the people were divided into groups of 50 and 100, so if the groups are close to equal, there are 133 groups of 100 and 134 groups of 50 (267 groups in total). With large groups like that, the distance between the center of one group to the center of another was probably around 30 meters (close to 100 feet). The disciples had to pass around a lot of food to each group, so they likely stayed all together. Thus, they had to walk a 26700 meters to go to each group, and since the people ate and were satisfied, they probably wanted seconds, so that's actually 53400 meters with an average velocity of 1.4 m/s (the average walking speed). Using kinematics, we know that v = x/t, so t = x/v. Therefore, it would take 38143 seconds for the disciples to pass out that food, which is about 10 hours and 36 minutes. That's a lot of time!
    By understanding physics, you can appreciate the incredible awe of this miracle.
  11. DavidStack

    Final Blog Post

    By DavidStack,

    Well this is kind of bittersweet, finally being done with blog posts but also realizing that high school is completely over, as is Physics C with a fantastic teacher. I've learned so much during the year, from angular analogs to retarding forces to induction to the sheer brilliance of Walter Lewin's ability to draw a dotted line; it's been quite a year. I've appreciated this blog posts as much as I've hated them, mostly because they forced me to truly learn the stuff that I write about. And now when I struggle with physics in college, I'll always be able to go back to APlusPhysics and ask for help. I encourage anyone and everyone to take Physics C - it's certainly challenging but I can't see how you could regret it. So, farewell APlusPhysics, I'll likely come crawling back in no time at all.
  12. DavidStack

    First Post (Finally)

    By DavidStack,

    So good thing I spent half an hour trying to figure out how to make a post, and then thought, 'hey, maybe I should actually look at that sheet that Mr. Fullerton gave us,' only to realize that all I had to do was verify my account, and that I wasn't supposed to make my real name my user name. But anyways, here is my post. The first thing to know about me is that I love Jesus, and really the reason there's any need for you to know that is because that is why I'm taking AP-C Physics. I would love to become a Civil and Environmental Engineer, and create better water filtration and water collection systems for impoverished countries, much like the Ugandan Water Project, also using the civil side to help design more efficient infrastructure in these countries. I've been on numerous missions trips, most recently to Peru, and have discovered a love for serving others and teaching others about Jesus. In the class specifically, I'm excited to be challenged and start making connections to what I learn now and how I'll use that in the future, but I am a little anxious about discovering the many complexities of physics. And other than all that, you should know that I love the Bills (which obviously is thoroughly depressing), I really enjoy talking to people and hanging out with my friends and playing sports, and I quit when things get hard.
  13. DavidStack

    Good ole Sandy...

    By DavidStack,

    In the wake of the costly hurricane Sandy, its interesting to look at how physics explains the dangers of those extremely powerful winds. In my backyard, the gusts snapped a horizontal branch off of one of my trees on monday night, so I wondered how dangerous it would be if I was standing under the branch when it hit the ground. The branch was about 4 meters high. Assuming that the wind was moving completely horizontal and perpendicular to the branch, the branch would have had no vertical force acting on it, neglecting air drag. Thus, you can calculate the vertical speed of the branch upon hitting the ground with conservation of energy. K = U, so .5m*v^2 = mgh, so v = (2gh)^(1/2), so v = (2*9.8*4)^(1/2), so v = 8.85 m/s. The wind was moving at 35 mph (15.6 m/s), so that is the horizontal speed of the branch. Given these two speeds, the final speed of the branch is calculated by taking the square root of the sum of the squares, so v = 17.94 m/s (40.13 mph). I don't know about you, but I certainly would not want anything crashing into me at 40 miles an hour, so Sandy was dangerous even as she was cooling off.
  14. DavidStack

    Hot Rod

    By DavidStack,

    Hot Rod, arguably the greatest movie ever created, actually has quite a bit of physics incorported into it. The part I will focus on is when Rod fails miserably to jump the local pool. Barely making it halfway, Rod slowly spins forward while in the air and lands face first, bike and all, into the pool. His demise results from two things - lack of kinetic energy and conservation of angular momentum. While he did have a ramp leading up to the jump, it was not nearly big enough to clear the pool. Thus, his moped could not gain enough speed, which meant that he didn't have enough kinetic energy to convert to potential energy to reach the height he needed to reach. Not only so, but while taking off the jump, Rod leaned forwards. Since he couldn't control his angular momentum while suspended in the air, that initial momentum continued while he was in the air, leading him to rotate forward ever so slowly and land on his face. All in all, Rod clearly didn't understand the physics needed to clear this jump. However, he made the movie hilarious, which is all that matters I guess.
  15. DavidStack

    Kerbal Project

    By DavidStack,

    After spending quite some time with the Kerbal project, I am starting to understand how the program works. Building the biggest rocket possible doesn't really work; you need a balance between fuel level and weight, aerodynamics, the necessary seperators and parachutes, and a knowledge of when to hold off on burning fuel, the SAS, and other things like that. Thus, our first couple launches were not as successful as we would have hoped, but as we learned to decrease the drag force by improving the rocket's aerodynamics and not just stack fuel tank on fuel tank, which decreased the engine power by making the rocket too heavy, we started having successful launches. While the game is definitely interesting and I have learned a decent amount about space exploration, I wouldn't mind if there were other options for an end of the year project, given that I don't necessarily love video games and there are topics that I would love to explore, especially things involving engineering. So to recap, the program is a great idea for an end of the year project, but other options would be much appreciated.
  16. 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.
  17. 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.
  18. 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!
  19. 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.

  20. DavidStack

    Moon Boots!

    By DavidStack,

    Reflecting on my Christmas presents, I immediately think of the incredible gift that my sister Julia got me, these super comfortable moon boots. But why are they so comfortable? As with most things, physics offers an explanation. As we've learned way back with momentum, impulse is equal to the force multiplied by the change in time. Impulse also equals the change in momentum, and given that momentum is conserved when only conservative forces are acting on the object, the impulse does not change. Therefore, when the time that the force acts on the object is lengthened, the force felt by the object decreases. This is where the moon boots come into the scenario. Ordinary sneakers have little padding between the sole of the sneaker and the wearer's foot, so the time of impact from the floor to the foot is relatively short, meaning a relatively large force. The moon boots, on the other hand, have a great deal of padding, extending the time of impact of the wearer's foot and the floor. This reduces the force felt by walker and provides them with a lighter, more comfortable feeling as they feel almost like they are walking with less of a gravitational force (as on the moon, hence the name of the shoes).
  21. 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.
  22. DavidStack

    Muscle Memory

    By DavidStack,

    The brain is an incredible thing and is refered to as the world's smartest computer for a reason. I've recently grown to love muscle memory as it helped me greatly in performing in a musical this past weekend. Even though I would be in the middle of a dance number and completely forget the next part of the dance, my body would do the moves for me without me even thinking about it. This is because of muscle memory, as our bodies build neural pathways after doing a certain activity over and over again so that when presented in a situation, we naturally do what we've done so many times. Even though I would feel like I didn't know what to do, the procedual memory of doing certain moves on the stage on cue with certain music and lights led to me somehow almost always doing the right thing. I also just realized that this doesn't necessarily have to do with physics, but I still think it's a really cool topic, and now I can dance like this guy.

  23. DavidStack

    My Cookie Problem

    By DavidStack,

    Alright Charlie, I'm writing a cookie problem just for you. You might need to get the cookie from Liz, but I figured I'd write one since you said there haven't been enough. And continuing with the Disney theme, here goes: Mulan is curious about how current and magnetic field interact, so she inserts her charge filled sword (which temporarily acts like a wire) of length 1 m into a magnetic field of 2 T in the postitive i direction, creating a force a 2.5 N in the positive k direction.

    1) What is the direction and magnitude of the current?
    2) What is the funniest movie David has ever seen? (You need to answer this correctly in order to get the cookie.)
  24. DavidStack
    Given that this is my first post of the second quarter, it's fair to say that I am not always on top of my Physics work. And since I have not been doing as well on our tests as I would hope, I have a couple new year's resolutions regarding Physics:
    1) Do my blog posts before the weekend that they are due!
    2) Continually look over equations so as to hammer them into memory
    3) Study more diligently before tests instead of "hoping for the best" as I often do

    With these resolutions, hopefully I can see my test scores rise and my stress levels fall (known as David's theory of the inverse relationship between stress and test scores, which will hopefully prove true).

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