Sound from an object moving toward you sounds higher in pitch than the same sound coming from that same object moving away from you. This phenomenon is called the Doppler effect. While more noticeable from fast and loud vehicles like speeding cars and trains, the doppler effect can even be observed from an electric skateboard. The Doppler effect occurs because the sound waves emanating from the moving object are closer together in front of it than they are behind it. The speed of sound through air is constant, so when Owen yells while as he rides, the sound always travels from his mouth to the microphone at the same speed. The difference is that when Owen rides toward the microphone, he moves forward slightly between each individual peak of the sound wave he makes. This means that the sound reaching the microphone effectively has a higher frequency and therefore a higher pitch than if Owen was stationary. The opposite is also true as he rides away. Owen travels a slight distance away from the microphone in between each sound wave crest that he generates, making the frequency and pitch lower. While Owen could have easily lowered his voice while passing the microphone to fake this experiment, a camera and microphone on the board itself proves otherwise. Because the board-mounted camera always maintains the same distance from Owen the pitch remains constant.
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The Great Ball Contraption is a series of Lego machines built to move marble-sized balls from one machine to the next. These machines, called modules, are constructed to a set of standards so that any module can feed balls into any other. Many builders will bring their modules to Lego fan conventions, like Brickfair, and arrange them together in a loop for continuous circulation of balls. https://www.youtube.com/watch?v=HvJg3YoehYk&t=1610s I've build many of these modules, but my most complex one to date appears at 10:08 in the video. It works by dropping the balls one at a time into a barrel, where a small electric motor pulls down a spring loaded arm. Once released, the arm accelerates the ball upward and around the underside of the arch, eventually landing on the other side. I designed this module to be overly-complex and entertaining as possible. As a result, there are many different kinds of energy being converted into one another as the ball travels from one end to the other. Almost all modules are powered by an electric motor, and all modules must lift the balls to a certain height to dump them into the next module, so the simplest module would use a motor to convert electrical energy from an outlet into kinetic energy of the spinning motor, and then use a simple lift or conveyor to transfer some of that kinetic energy to the balls in the form of gravitational potential energy. However, this module first takes the electrical energy from the wall and converts it into kinetic energy of the motor, but then converts it into elastic potential energy by compressing a spring. when the spring is released when in contact with the ball, it transfers some of its elastic potential energy into the ball's kinetic energy. As the ball travels up the arch, some of its kinetic energy is converted into gravitational potential energy, only to be converted back into kinetic energy as it continues down to the other side. However, the ball does gain a small amount of gravitational potential energy through this process, as it leaves the module slightly higher than it enters. The conversion from kinetic energy of the motor to elastic potential energy and then back into the ball's kinetic energy is crucial to getting the ball up to such a high velocity to travel on the underside of the arch. In order for the ball to achieve such a high velocity as it exits the barrel, it must experience a very large force and therefore a high acceleration. The motor itself is incapable of exerting such a large force that would accelerate the ball to such high speeds. With a gear reduction, the motor can exert a large torque and therefore a large force at the cost of speed The spring acts as an intermediate step. The motor exerts a comparatively small force on the spring to compress this, but does it over a relatively long time. However, when the spring is released, it exerts a large force on the ball over a short period of time. The impulse that the motor applies to the spring and the impulse the spring applies to the ball are the same, however, the spring is able to reach high enough speeds to change the ball's momentum enough to make it up and around the arch. The spring itself is fixed to a pivoting arm which forms a class II lever. The spring exerts a large force on the lever arm but is connected at a small radius from the pivot point, creating a torque. To compress the spring, a rotating arm attached to the motor exerts a force on the spring arm, but at a larger radius from the pivot than the spring. This means that the motor exerts a smaller force to create a torque greater than that created by the spring, at the cost of having to exert this torque over a longer distance. Once traveling out of the barrel, the balls undergo circular motion as they pass through the underside of the arch. There is no wall or guard underneath the balls. The inside of the arch creates a centripetal force which keeps the balls in a circular path, similar to the tension force created by swinging a ball in a circle from a string. The faster the balls travel, the greater this force is, so the balls must be traveling at a high velocity to overcome the force of gravity.
After some road work, an intersection is now safer for drivers. The only alteration made was to increase the radius of the turn the cars make when turning right. This makes the turn safer because of the principles of circular motion, which state: Fc=(mv^2)/r In this equation, Fc is the magnitude of the force of friction a car's tires need to keep the car moving in circular motion. If this force is greater than the force of friction between the car's tires and the road, it car will skid out of control. To minimize this risk, the radius of the turn must be made as large as possible to decrease the amount of friction needed for the car to stay in the turn. This is because in the formula, The frictional force (Fc) is inversely proportional to the radius of the turn, meaning that as the radius gets larger, the frictional force gets smaller. This is especially important in winter when there could be ice one the road. The coefficient of friction between tires and ice is much less than between tires and asphalt, meaning that a car with the same weight will not exert as much frictional force on ice as it would on dry asphalt. The radius must be even larger to reduce the chance that a car could slide off of the road in icy conditions.
I was somewhat caught off guard by this test. I had a good sense of each of the concepts in our One-Dimensional Kinematics unit, but I lacked the experience in putting these concepts together as many of the problems did. In retrospect, I should have focused my studying on practicing these kinds of problems. The math aspect in particular was not what I expected. While I had no troubles plugging in variables into kinematic equations to solve basic problems, I lacked the ability to properly manipulate the equations to aid me in more complex ones. I attribute this to my intuitive sense of solving simple physics problems, so I was not prepared to rely so heavily on math. This test has definitely made me rethink how I will study for future assessments so hopefully I will be less surprised in the future.
AP Physics 1 is a good fit for me. As an aspiring engineer, I feel that is is important that I have a good understanding of physics before I go to college. After looking into Flint Hill's different different AP Physics options, I came to the conclusion that taking AP Physics 1 and 2 would allow me to focus more on material that I am interested in, like mechanics and electricity. After getting a glimpse of the workload of the class, I think that I am in the right place, as I want to be pushed and challenged without being worked to death. Additionally, I did well in Freshman Physics which gives me a small jump on the material we are learning. Overall, I am happy with my course selection and intend to stay in AP Physics 1
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Zach Pabisis a high school junior writing about his adventures in physics. Archives
April 2019
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