Jump to content

APlusPhysics Blogs

Showing blog entries posted in for the last 365 days.

This stream auto-updates     

  1. Yesterday
  2. Rotation recap

    Our last unit in AP physics c was rotational motion. In this unit we learned about rotational kinematics, dynamics and momentum. Rotational kinematic is very similar to translational kinematics because the same kinematic equations are used. The difference is that instead of displacement roation has the change in the angle. Instead of translational velocity and acceleration, rotational motion is calculated with angular velocity and acceleration. As far as dynamics go, rotational motion has a very significant concept that separates it from translational motion. It's moment of inertia. Moment of inertia is the measure of an objects abilty to resist rotational motion. It could be compared to inertial mass or just mass. The other importance to rotational dynamics is the concept of torque which is a force that causes rotation mesured in Newton*meters. Torque is equal to the moment of inertia of the rotating object times its angular acceleration. Torque is also equal to the cross product of force and the distance from the axis of rotation that force is applied. Rotational dynamics is important for solving many different problems involving rotation. Rotational or angular momentum is the measure of how difficult it is to stop a rotating object. It can be calculated using the equation L = moment of inertia * angular velocity. Angular momentum is also equal to the cross product of the objects radius and its translational momentum. It is important to know that angular momentum is always conserved, so in a closed system the intitial angular momentum is equal to the final angular momentum. Rotation is a very important topic because it is so useful in the world of science and engineering because not everything moves in linear motion. For instance our solar system can be studied using rotation since our planets move in rotational paths.
  3. Last week
  4. My bike and I

    Provoke not the ire of I. Quick to temper, quick to wit. Verily I see the serpents' lie, perch'd low to befit. Bade not beget a quarrel but beget one indeed. Riven from I alike a valley cleft. Oft I wonder'd my words would have heed but I discover'd a friend bereft.
  5. Railguns

    Two words, ten letters: gun on rails
  6. Top-making

    I totally missed out, did not I?
  7. Engineering Design Process

    How come I was not invited?
  8. Earlier
  9. Spinning Top

    On Monday we were given a problem: Make a spinning top. We had two paper plates, six pennies, a sharpened pencil, and some tape. With no further instructions given, we were left to our own devices to solve the problem. Though I cannot speak for my partner, I can say that I was not thinking of the engineering design process at the time. However, the engineering design process was precisely how we were going about our task. We had a problem to solve and we began by constructing our solution. We taped the six evenly spaced pennies to the outside of one plate, then put the other plate on top. We poked the pencil through (roughly) the center of the plates. Then, we tried testing our results. When it didn't work perfectly the first time, we made adjustments. We would try placing our mass at different heights on the pencil. We found that it worked the best when it was lower. However, we did not pick up that we should have snapped the pencil in half to make the top more stable. We learned this after. Moment of inertia was crucial in this lab because a higher moment of inertia would mean the top would have greater angular momentum. Increased angular momentum would mean that the top would be more resistant to change in its rotational motion and stay spinning longer. We tried to maximize the moment of inertia of the top by placing the mass (the pennies) by the edge of the plate. This way, the radius was greater.
  10. Spinner Reflection

    On Monday during physics class, we were asked to create a “top” that would spin for a long period of time. The materials we were given included two small paper plates, a pencil, six pennies, and tape. At the end of the lab experiment, we were asked to answer the following questions in a blog post: How did today's opening activity relate to the engineering design process? The engineering design process involves designing, building, and testing something. This relates to what we did in class because we had to brainstorm solutions to the given problem, and then we built, tested, and redesigned various models. For example, we tried moving the pennies closer to the center of the plate, and then we tried moving them farther to the outsides. We also experimented with moving the plates farther up and down the pencil. Unfortunately I carelessly poked a hole through the plates that was off-center and this impacted our results. Oops!In the end, we learned that the task would've been much easier if we had snapped the pencil in half. How did today's opening activity relate to moment of inertia and angular momentum? If friction did not exist, the top could keep spinning forever. But because there is friction, you want to maximize the angular momentum of the top so that it takes longer for friction to stop the top. You can increase angular momentum by increasing pieces of rotational inertia such as mass and how far away the mass is from the center (or the radius). We did this by putting all six pennies evenly spaced on the outside edges of the plate.
  11. Top Lab

    The Engineering design process is a series of steps that engineers go through to create a product of some sort. The process can be very repetitive at times while going through a process of trial and error. The lab that we did in class demonstrated the engineering design process. We were given two paper plates, six pennies, a pencil, and tape to create a spinning top. First we came up with an idea that we thought might work so we constructed a top that had a pencil through the center of a plate with six penny's evenly spaced around the plate but not to the edge. The plate was at about the center of the pencil. This failed because the plate was not stable enough on the pencil so we added the other plate to the bottom of the first plate to stabilize it a little more. We also lowered the location of the plate to be more toward the bottom of the pencil. This would decrease the wobbling because there would be less torque on the pencil if there is a smaller distance since Torque is the cross product of F * r. These two adjustments improved the top but it still was not spinning perfectly. Something that would have made it spin a lot better would be to shorten the length of the pencil. This would have gotten rid of the weight at the top of the pencil to decrease the net torque even more. Moment of inertia was a big part of this lab because moment of inertia is an object's resistance to rotational acceleration. An object with the least possible moment of inertia would be the most successful. Angular momentum was also a very important part of this lab because angular momentum describes how difficult it is to stop a rotating object. Therefore, an object with the greatest angular momentum would be very successful in this lab because it would take a lot of torque to change it.
  12. A Summary of Our Top-notch Design

    The objective of the lab TheNightKing and I performed this week was to create a functioning top with the given materials of a pencil, 2 paper plates, 6 pennies, and tape. In relation to the engineering design process this would be the problem or objective we need to focus our ideas around. Our next step would be research, but , due to our lack of time, we pulled from our knowledge gained throughout this past unit and our previous year physics. One of the main principles to keep a top up is angular momentum. The equation for spinning angular momentum is rotational inertia x angular velocity. So we need to spin it as fast as possible and, most importantly, we need to give it the largest quantity of rotational inertia possible. So, ignoring the pencil rod at the moment and plates, we knew we needed to get the pennies as far away from the center as possible since the equation of a mass away from the axis of rotation for a given mass is mr^2. So, by increasing the radius, we could get a larger quantity of spinning angular momentum. Stating and listing the requirements would be the next step in the engineering process, but we were already given them in the objective. The next step is to brainstorm, evaluate, and choose solution. We chose to use the pencil as our main post and then centered and poked it through the two plates. We then taped the pennies to the outskirts of the plate as this would put their mass at the farthest points away from the center of mass as possible. Our prototype was created and now we began testing. The top originally wobbled so much that it wouldn’t spin so we adjusted the pennies. We Adjusted until we had the top balanced which decreased the wobble dramatically. That being said, it was not as stable as we ideally would like. This is when FizziksGuy gave us a nudge in the right direction by asking which part was the most unstable. We both noticed that it was the very top of the pencil. In our efforts to make the top more stable, we broke the pencil to a fourth of the size and therefore dramatically lowering the center of mass. Now the top was much more stable as the distance of the center of mass from the ground is substantially less than before. After all this testing, we felt our top was substantially more stable and adequately addressed the problem, being able to spin for longer than 30 seconds at a time. The last step in the engineering design process is communicating our results which coincidentally are all explained above. Engineers are used not only to create solutions, but to improve on the efficiency of current ones, so to this effect, had we had a longer time frame I am sure the results could have been even better. As always thanks for reading! - ThePeculiarParticle
  13. This past week, we did a small partner lab. Our mission was to make a top out of the following materials: 2 paper plates, a plain wood pencil, 6 pennies, and tape. The top also had to be able to spin for more than only a few seconds. However, there were no instructions other than to make a top. Immediately, each student in the room with his or her partner immediately began undergoing the engineering process, whether they knew it or not. The engineering process has steps to be done in this order -- Define the problem, do background research, specify requirements, brainstorm solutions, choose the best solution, do development work, build a prototype, test and redesign. We already knew the problem, and we were presented with a top to look at in the back of the room, so we already defined the problem and did a little research on tops. The requirements were to make the top with the materials provided, and the top must spin for more than only a few seconds. We brainstormed quickly and then talked about our ideas on how to make the top. We then chose to mix our ideas together to get the best solution possible and we discussed who was to make it and walked through it together. Soon, we had a prototype and we were able to test that design. If it did not work that well, we tried something new. This lab, in a nutshell, was a little simulation of the engineering process! This lab also shows a relationship between tops, angular momentum and moment of inertia. As the top spins, the angular momentum generated points straight up into the air, and if there were no friction, the top would spin forever because the momentum that holds the top up is forever conserved unless acted on by an outside force. The moment of inertia of the top is the rotational analog of the mass of the top. The angular momentum discussed above is the result of the top's moment of inertia times the rotational velocity.
  14. Creating a Top

    Wow! It is already December and we are working on rotation in class! Last year, this unit was one of the worst for me because I truly did not understand any of the concepts. I have started to figure out some of the equations and concepts but, I am going to have to work hard all this week in order to really understand the unit. In class last week, Mr. Fullerton gave us a challenge to solve. He gave us a pencil, two small paper plates and six pennies. Our task was to make a top that would spin for a longer period of time from those materials. For the blog post this week, we have to explain how this activity relates to the engineering design process. If I am being honest, I had no idea what it was and typed it right into the handy dandy Google. I found a website (sciencebuddies.org) which gave me the steps to the engineering process. Those steps are: Define the Problem Do Background Research Specify Requirements Brainstorm Solutions Choose the Best Solution Do Development Work Build a Prototype Test and Redesign I definitely think that all of these were used in the activity with some of them slightly combined and happening all at once. Our problem was creating the top that would stay spinning for more than just a few seconds. Our research came from the information that we could see coming from the actual top and our background knowledge from the physics we had been learning. The requirements came in the form of the items we could use to make the spinning top which were the pencil, paper plates and pennies. The next few steps were combined because of time and we began to use trial and error to try and build the top. Brandon and I immediately knew that the the plates would have to have the pencil going through the center. We tested out where the plates would have to go on the pencil and eventually found that it had to be placed towards the bottom of the pencil. On the plates we tested the different distances of where to put the pennies and ended up putting the pennies at about an even distance towards the outside of the plates. Our final aspect that we fixed to make the top spin longer was put a small piece of tape at the tip of the pencil to keep it from spinning around all over the table. After that, we had created a top that spun for a decent amount of time with the many aspects we changed and tested. The next question we have to answer is relating this activity to moment of inertia and angular momentum. For the moment of inertia, the mass and radius are the factors that change moment of inertia. Since we could not really change the mass of the object, spreading out the pennies to create a larger radius impacted the moment of inertia for our top. For the angular momentum of the top, the moment of inertia and angular velocity impacted the top and allowed it to spin for a longer period of time. These two concepts combined created the top with lots of trial and error for the perfect one. Until next time, RK
  15. Slingshot Engaged

    Over the thanksgiving break, I watched one of my favorite movies, Talladega Nights. The movie is about a race car driver and one of the moves that he frequently uses to win is called the slingshot. In this maneuver, the driver would get really close behind his teammate to draft up speed and be able to pass the car in front of them. At first I didn't understand how this worked, but I dived into some of the physics behind it to get a better understanding. The slingshot maneuver, which is also known as drafting, is not only used in race car driving but also in other sports such as cycling. In this imagw, you can see how drafting works and enables the second car to go faster. The second car gains speed when it gets right up behind another driver because the first car is keeping the second car from being impacted by wind resistance or drag forces. I watched cyclists use this technique in the Olympic events last year in order to gain an advantage. Towards the end of the race, the riders often go into a slipstream where the rider trailing gets really close behind the leader so that pedaling is easier because there is less drag force acting on them. Then when they have saved up enough energy, they are able to cycle past the leader and win the race. You can see this demonstrated in the video from the link below. http://www.nbcolympics.com/video/cycling-womens-road-race-finish This is a pretty clever technique that can change the outcome of sporting events and it was interesting to understand the physics behind it.
  16. Elevators are Evil

    This is about me, right?
  17. Aztec Spear Thrower

    An atlatl or spear thrower is one example of mankind's inherent knowledge of throwing spears well. The throw or "casting" involves acceleration, force etc. but the precise action that our mechanisms enhanced our early projectile weaponry is remarkable and telling of humanity's ingenuity. This device acts like an extension of the wielder's own arm amplifying the leverage, involving elements of the center of mass and whatnot, of the throwers arm and wrist. It also improved upon the stability of the cast using a rigid piece of wood or perhaps bone for an an atlatl instead of relying on the muscles of the arm. This balance in the throw is particularly important because the most effective strikes are delivered forcefully at the point of the spear, more pressure is applied at the very narrow end because of force per area. A selection of darts may use fletching to balance the projectile and these fins provide good lift or thrust due to air resistance. The amount of thought that our forebears put into killing things is notable because it is a point towards hallmark qualities that man has that animals do not, our high motivation and ability to plan. This is at the soul of humanity and I believe this is important to understanding our heritage and natural intuition as it is for supplementing our understanding of physics.
  18. Running Fast = Gaining Weight = Fun!

    I am similarly enthralled.
  19. The Wizard of Oz

    In Ap psych this phenomenon was called eyesight.
  20. The Sport of Pumpkin Chucking

    A trebuchet is a medieval siege engine that can launch a 90 gram projectile a distance over 300 meters.
  21. The Physics of Birthday Wishes

    How to make such an equation which results in the age of 27?
  22. We consecrate thanksgiving in the abundance that has come to us, not in vainglory but of thankfulness for our lot in life. With a class of a few, we know each other by name and are never far apart. These blogs keep our thoughts fresh and physics at the forefront. Really, AP physics C is a paradise. The packets are straightforward and with a bit of searching, the answers are conveniently there with little confusion on the whole. Our equations are adequate and fulfilling, they are means to an end and I am thank that my forebears had thought them. Thanks, to my teachers and my peers. This year will be worth it!
  23. Physics in English

    As a member of that same English class, I say we meme-orialize those moments as part of a happier, simpler time.
  24. The Weight of Air (and birds)

    Hold up, if lil peep is no longer with us and the peeps candy are modeled after ducks, is this post pretty much a eulogy. I selected option C in the very beginning so I should have some say in the prize given. A carton of peeps candy would do nicely.
  25. Quantum Leap

    This is the truth.
  26. But how did Sylvestor get across the ravine?
  27. Violin Blog 3: Tuning

    It's so cool learning about things in music and then learning why these things happen in physics. If you think about it, most of music is physics.
  28. What is Onix Made Of?

    That's a whole lotta math! Well, you know what they say... gotta catch em all. Or in this case, Gotta catch all of em, meaning all of this ginormous baby powder beast into a tiny pokeball.
  1. Load more activity

Terms of Use

The pages of APlusPhysics.com, Physics in Action podcasts, and other online media at this site are made available as a service to physics students, instructors, and others. Their use is encouraged and is free of charge. Teachers who wish to use materials either in a classroom demonstration format or as part of an interactive activity/lesson are granted permission (and encouraged) to do so. Linking to information on this site is allowed and encouraged, but content from APlusPhysics may not be made available elsewhere on the Internet without the author's written permission.

Copyright Notice

APlusPhysics.com, Silly Beagle Productions and Physics In Action materials are copyright protected and the author restricts their use to online usage through a live internet connection. Any downloading of files to other storage devices (hard drives, web servers, school servers, CDs, etc.) with the exception of Physics In Action podcast episodes is prohibited. The use of images, text and animations in other projects (including non-profit endeavors) is also prohibited. Requests for permission to use such material on other projects may be submitted in writing to info@aplusphysics.com. Licensing of the content of APlusPhysics.com for other uses may be considered in the future.

×