For the blog post, I used a slinky to demonstrate different types of waves and other things that we learned about waves in this unit. First, I demonstrated the difference between longitudinal and transverse waves. A longitudinal wave is when the oscillation is parallel to the direction of motion, and sound waves and pressure waves are examples. On the other hand, a transverse wave is when the oscillation is perpendicular to the direction of motion, and a rope wave or a light wave are examples.
When I pull part of the slinky towards me, this increases the tension of the slinky. We learned that as tension increases, so does the velocity of the wave, and I can confirm this by comparing the velocity of these waves to the initial ones, and I used approximately the same force on the slinky in both scenarios. Finally, I tried to create a standing wave, where there are clearly defined nodes and antinodes due to constructive and destructive interference and reflection. Although it definitely isn't perfect, the snapshot that I show looks pretty close to the third harmonic. In a closed-closed system, the wavelength of the third harmonic is 2/3 times the length of the slinky. The things we learned in the waves unit can apply to lots of things in life, from sound, to light, to the movement of a slinky and beyond. I think this video provides a summary of the most basic concepts of the unit, and they can be used to expand to the more complicated things like the Doppler effect or finding more harmonics.
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With Spring Training starting up and opening day about a month away, I wanted to do my application blog post on baseball. I thought about different aspects of the game, and then I connected them to what I have learned this year in AP Physics 1. I hope I knocked it out of the park! Motion An interesting new philosophy in the MLB is about the importance of launch angles for hits. According to this article, written during the first half of the 2017 season, hitters are increasingly looking to hit the ball in the air. Daniel Murphy is a leader in this movement because he advocates for “air balls,” or trying to hit fly balls instead of ground balls. This article calls the sweet spot for hits to come at launch angles between 25 and 35 degrees. We learned that the optimal angle for the greatest horizontal distance for a projectile is 45 degrees because this combines time in the air (determined by vertical velocity) with distance traveled (horizontal velocity). With this physics knowledge, I was confused while reading this article because I would expect the sweet spot to be 45° solely based on projectile motion. However, the initial velocity is another important part of the motion of a baseball, and in order to make solid contact with the baseball, it has to come at an angle lower than 45° because otherwise the bat wouldn’t hit the center of the ball. Forces and Motion Here is a physics problem about both motion and forces that can be related to baseball that I found on this website. Sliding into a base causes there to be a force of friction that slows the runner down. This is an oversimplified force diagram because there is also air resistance to take into account, but it helps us solve a problem to find the acceleration of the runner as he slides into second base. Rotational Inertia Two strikes. You step outside of the box and hear your coach remind you to choke up and put the ball in play. Why is this though? The bat undergoes rotational motion throughout a swing, so we can apply physics concepts to help understand this sport. Rotational inertia is an object’s resistance to a change in its angular velocity. It is determined by the distribution of the mass of the object in relation to the fulcrum, or the axis of rotation. The farther away the mass is from the pivot point, the more difficult it is to change its rotational motion so the greater its rotational inertia. Using a regular grip means that the vast majority of the bat’s mass is far away from the axis of rotation, so the bat has a large rotational inertia. However, if a batter chokes up, now the mass is closer to the axis of rotation (smaller radius). This means a choked-up grip causes less rotational inertia, so the batter doesn’t need to apply as great of a torque to affect the motion of the bat. This can be useful in a two strike situation because it gives the batter more control and time for last minute adjustments in order to avoid striking out. Linear and Angular Momentum This Mythbusters article explains why runners slide into bases instead of running to them, and it relates to both linear and angular momentum. If a player runs into second base, he has to slow down in order to avoid overrunning the base and being tagged out. Therefore, the runner must decrease his velocity, which decreases linear momentum (impulse in the opposite direction) which means that it takes longer for the runner to reach the base. On the other hand, starting the motion of sliding causes some linear momentum to become angular momentum (rotate into a headfirst or feet-first position), so the runner doesn’t lose as much momentum as he would by decreasing his translational velocity. Then the runner relies on the friction with the dirt to slow down and then his hands or feet to stop on the base. Here is an interesting video about the physics of sliding and why it is better to slide headfirst than feet-first. Translational and Rotational Kinetic Energy This article talks about how Statcast can now track the different spin rates for pitches. Based on the image below, the key for good pitchers is to have both high velocity and a high spin rate on pitches. I'm going to solve another problem from this document that discusses both translational and rotational kinetic energy of baseball pitches. There is a short summary of some of the ways physics can be applied to baseball! I'm looking forward to this season and I hope the Nationals do well!
Originally, this turn had a very small radius, but the construction increases this radius. The equation for centripetal force, or the force an object undergoing uniform circular motion experiences, is shown above. If the turn has a small radius and the mass and velocity of the car remain constant, the centripetal force (aka the net force) needs to be large in order for the car to maintain circular motion. The centripetal force comes from the friction force by the road on the car, and this reaches a maximum value that might not be great enough to maintain circular motion. During the winter, slippery roads would mean that there is even less friction and a smaller centripetal force, so it is unlikely that a car would be able to maintain circular motion.
On the other hand, increasing the radius decreases the necessary centripetal force because the radius is in the denominator of this equation. This means that the friction force present might be enough to keep the car in the turn instead of drifting out like it would with the smaller radius. Therefore, increasing the radius of the turn makes the turn a lot safer for cars, especially during the winter with icy conditions. I felt pretty confident going into this test because it followed the freshman physics curriculum, and I had worked with position vs. time, velocity vs. time, and acceleration vs. time graphs in calculus last year. I was able to complete the Mastering Physics assignments pretty successfully because I am comfortable with using the equations and switching between the different graphs.
I spent a lot of time working on my content page for this unit, and I think this helped me a lot. I didn't feel like I needed to do excessive studying once I had completed this, so I just read over it a few times to review. I also filled out the majority of the practice packet that you gave us. I found the Dynamic Study Modules very useful and some of the information I learned on that tool was very useful on the test. The team test was beneficial because since I was able to complete this effectively, it made me realize I was prepared and increased my confidence for the test. The test itself was a little bit harder than I expected, mostly because it had more complex problems than the team test did. However, overall I think I did a good job, and I think I will get a good grade, especially with the curve. Other than a few difficult problems, I was able to complete the rest of the test with confidence in my answers, so I left the room satisfied with my efforts. So far, I am enjoying this class and I think I am right where I should be. Although I know the class is going to ramp up to be a lot more difficult than it is currently, I think I have solid grasp on the basic concepts of physics like the relationships of position, velocity and acceleration.
Based on my friends who took this class last year, it was a lot of work and they were frustrated with how difficult the assessments were. I am nervous about the tests in this class because I have never been in a class where getting a 60% raw score could lead to a B or and A. It will be a different approach to walk into a test, only feel confident with a small portion of the test, and be ok with that. However, it will be a nice surprise when the curve is factored in to our scores. I also know that this class is more about understanding concepts and applying them to problems than it is memorizing formulas, so I am prepared to work very hard to master the concepts and this should help me with the tests and quizzes. I signed up for this class because Physics was my favorite subject between Physics, Chemistry, and Biology, and I wanted to try an AP Science before I graduated from Flint Hill. I am ready for any challenges that this brings, and I am confident that I will be able to persevere through them. |
AuthorMy name is Kathleen Boyce and I am a 12th grader at Flint Hill School who is taking AP Physics I. Archives
April 2019
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