For my waves unit blog post I decided to explore the doppler effect, something I did not really get initially. I thought this lab would be a great way to understand the concept of the doppler effect by using a real life example. The Doppler effect is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. For a source and observer with no relative motion, the wavefronts are all centered at the source at all times. Observers on any side will hear the frequency of sound from the source. The change in frequency results in a change in pitch. You can see this when my car moves past the camera, as the sound gets "louder" as it gets closer. As the car approaches the pitch increases, but as it is moving away the pitch decreases. The reason this happens is because with the doppler effect, the waves are 360 degrees. This means that as the car gets closer to the camera's microphone, the wavefronts are much closer together, hence, creating a higher frequency. When the car gets farther away from the camera, the wavefronts of the sound waves are much farther apart which decreases the frequency. The waves still travel at the same speed, the only thing that changes is frequency and wavelength. The diagram below demonstrates how wavefronts change as the distance changes with the observer and the car.
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There's a million ways to throw a football, but the most efficient way is only determined by its physics. Here I will explain the physics that goes into throwing the perfect football with Tom Brady as an example. Projectile Motion (2D Motion): Assuming there is negligible air resistance, the only force acting on it is the force of gravity. Since there is no rotating force acting on the object, it does not experience any external torque. Therefore, the only thing it experiences is the translational acceleration due to gravity. The quarterback can control three factors: the angle he throws it, the velocity of the ball as it leaves his hand, and the rotation he puts on the ball. When throwing a football, quarterbacks have to consider the angle they throw it. A higher angle means, it spends more time in the air. When the quarterback is throwing the football for a shorter distance, he does not need to use a higher angle because he will need to throw it in a short period of time. It takes the receiver a short amount of time to get to the shorter distance, which allows the quarterback to throw it quickly. The defensive players will have less time to react the less time the ball spends in the air. Furthermore, quarterbacks will throw at a higher angle when throwing long distances so that it has more air time. The receiver will have more time to get to the final position for the catch. Evidently, time plays a big role in throwing the football. The velocity of the ball is in the vertical and horizontal directions. With the quarterback throwing it at a higher angle, the ball will have a higher vertical velocity than horizontal. If he throws it at a lower angle, it will have a higher horizontal velocity and a slower vertical one. https://entertainment.howstuffworks.com/physics-of-football1.htm Forces: A force is a push or a pull exerted on one object from another. A quarterback throwing a football is an example of a force that makes the football fly in a game. There are three forces acting on the ball as it is being thrown, there is the force of gravity, the applied force by the person, and there is the force of friction by his hand. The spiral that the ball gets is caused by the force of friction. If there was no force of friction, the quarterback’s applied force will not be enough to create a perfect spiral. This can be seen in wet conditions where the quarterback has less a less force of friction on the ball and it leaves his hand wobbly and without a sufficient spiral. As a result, the ball does not travel as far of a distance, and it travels much slower. Energy: When Tom Brady throws the football, he keeps a short range of motion so that he is able to produce more chemical energy within his arm muscle groups. The chemical energy turns into kinetic energy that is transferred onto the ball. He uses a short range of motion to reduce time and to maximize energy output. If he used a larger range of motion, he would not have enough time and he would not be able to generate enough energy, hence making the ball travel slower and at a lesser distance. Tom Brady maximizes his arm movement and uses chemical energy from his abdomen muscles and his arm muscle groups to maximize the kinetic energy output of the ball. His short range of movement helps him move the ball quickly and efficiently in a short period of time. Momentum (Does not include throwing the football): The game of football is not only an offensive game, but a defensive game. When the quarterback gives the running back the ball, the running back has to penetrate the line of scrimmage with a lot of momentum. Momentum is a product of mass and velocity, which means the faster the person runs, the more momentum he has. That also works for mass, the bigger the mass, the more the momentum. So when a running back is gaining velocity, he increases his momentum so that he can get through the line of scrimmage and also be able to break tackles. As a defensive player, to stop him, by changing his momentum, a tackler must apply an impulse in the opposite direction. In order to beat the offense, defensive players should generate more momentum that allows them to literally stop the offense. Because impulse is a product like momentum, the same impulse can be applied if one varies either the force of impact or the time of contact. Impulse is the product of force and change over time. Therefore, if the running back has a lot of momentum, the defensive player can use less force over a longer period of time in order to stop the offensive player. This is useful when the offensive player is much larger and has more momentum because it will help the defensive player exert an impulse to stop the offensive player. Also, players can exert a large force over a short period of time to accomplish the same thing. For example, Aaron Donald exerted a large amount of force over a shorter period of time to stop Tom Brady, which he evidently did. He exerted an impulse that exceeded Tom Brady's momentum. https://www.wsj.com/articles/new-england-patriots-win-super-bowl-liii-11549249520 Rotation: If an object is spinning, there is an angular momentum to the right. The more rotational momentum the ball has, the more external torque is needed to set it off its path. When the ball has more rotations per second, it means it has more angular velocity, which then means it will have a higher angular momentum. Therefore, when Tom Brady throws the ball quickly, his spiral on the ball will generate more angular momentum which will keep the ball on its path. If he does not spin it, any other external force will be able to change its orientation and direction, making his passes to Julian Edelman harder to catch. It can also end up a significant distance from its intended destination. But when he does put a spiral on it, it will make it harder for external forces to offset the ball, which means when pass rushers attempt to block the ball, they will have to exert a large torque to actually affect the ball’s movement. In addition, the perfect spiral has a centripetal force which means that the ball will be far more stable. The faster it is spinning, the more stable it is. The spiral makes it easier for receivers to see the ball, predict its position, hence, making it easier to catch. What makes Tom Brady so great is that not only does he have the ability to throw a ball a long distance, but to throw the ball where he wants it to go, and throwing a tight spiral is essential to that. https://giphy.com/gifs/perfect-tom-spiral-iYDdp9Sj7FFiU
http://hyperphysics.phy-astr.gsu.edu/hbase/cf.html In the first picture, the radius of the turn is much smaller. In the second picture, the radius is evidently larger than that of the first picture. If in both scenarios the cars have the same mass and velocity, the smaller radius would require a much stronger force in order to follow the circular path safely. In the equation Fc= mv^2/r, it can be seen that if a larger radius is put into it, it will show that a smaller amount of force is needed to follow the circular path. In addition, the equation shows that the radius is inversely proportional to the centripetal force, which means that the bigger the force, the less the radius is. Therefore, making the radius bigger in the second scenario made the turn much safer as a much less force is needed for a car to follow circular motion.
This centripetal force is provided by the frictional force on the car by the road. If this force is larger than that of the frictional force, the car will release from its circular path and skid out of control. This becomes especially dangerous during cold weather conditions. If there is ice on the road, the frictional force between ice and the tires of the car is very little compared to the frictional force between the car and dry asphalt. If anything can be learned from this example, it is that a larger radius on a turn will create a much safer path for the car to follow. My first AP Physics 1 test was taken today and I thought I would feel better about finishing it, but it was quite the opposite. It was a lot harder than I anticipated because while studying, I practiced easier examples and practice questions. I felt less prepared than I should have because I did not practice questions with the same level of difficulty like on the test. Not only did I not practice examples well, I did not study well either. I only prepared by watching kinematics review videos on Khan Academy and by doing the homework on MasteringPhysics. I could have done much better if I had taken the time to really study the material and do the harder questions. This caught up to me in the test because for the free response questions, I did not know how to apply my knowledge and understanding of kinematics into my answers. I was simply lost on how to answer these questions. Although, I did find easier parts of the exam that included interpreting position vs time graphs, velocity vs time graphs, and acceleration vs time graphs. In the future, I will commit more time to studying and understanding the concepts fully.
AP Physics 1 has been a great class so far. I enjoy the experiments we do because they help me learn all the fundamentals of the unit we are taking. Although, I do not entirely know whether I am in the right place or not. I am most concerned about the heavy workload and not being able to keep up with it. I am looking forward to doing lab experiments and learning how to properly interpret the data.
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AuthorSami Khleifat: Junior studying AP Physics 1 at the Flint Hill School Archives |