To demonstrate the doppler effect, I got a friend to help me show how the doppler effect works when driving past someone, while honking. I acted as the driver, while he acted as the observer. He recorded 4 separate scenarios. First, to get a baseline, I was stationary in my car, and I honked the horn. Second, I drove towards my friend, while he stood still and recorded me honking as I drove past him. Third, we drove towards each other, while I honked the horn, with him recording. The speed for each of these scenarios was always 10 mph. The following are the audio clips of my recordings: This is the first observation: the car is stationary and I honked. If you listen, this has the lowest frequency, since the doppler effect doesn't apply right now. This is the second observation: The observer is stationary, recording, and the car drives by them, while honking. This frequency is greater than the standing still honk, due to the doppler effect. This is the third observation: The observer (recording) is driving towards another car that is honking.This frequency is greater than the 2 previous cases. As you can tell from the audio clips, the pitch gets progressively higher, with the double pass by having the highest. This is due to the doppler effect. As a sound originating from a stationary object wave travels towards you, you hear the waves in the same intervals. As an object is traveling towards you while making a sound, the waves bunch together, so you perceive more waves over the same time. Hearing more waves over the same time will increase the frequency. This is even more prevalent for 2 objects moving towards each other because the effect is essentially doubled (when both cars are moving the same speed).
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Since I got my driver's license at the end of last school year, one of the best advents of senior year has been my ability to drive. It's one of the first steps towards independence, as you don't need to rely on your parents to do everything involved in going somewhere. It's made senior year a lot better, and I know that there is a plethora of physics involved in driving, so I think it's a good choice for this blog post. To cover all of the units, I will go over the Motion, Forces, Energy, Momentum, and Rotation. Motion and ForcesThe principles of Kinematics and Forces can be used to determine/predict the motion of a car. I drive an automatic car, so for the purposes of this explanation, I will talk about automatic cars. There are two petals on every automatic car: the gas and the brake (duh). The gas petal controls the car's acceleration and the brake is used to slow down the car through friction. When you press on the gas petal, the chemical potential energy stored as gas is converted to kinetic energy that pushes the car forward (I will talk more about the mechanics of this when I talk about rotation). When a car is moving, several force are acting on it, including gravity, normal, friction, drag, and thrust. Gravity and normal force cancel out if you're not on an incline (if you are the gravity force will act downward, causing your car to have more of a force down the incline). Drag is negligible at low speeds, but as your speed increases, drag does too. This is also true for friction, but since the wheels are spinning, they don't generate as much friction as a sliding object. This is why cars have a terminal velocity (the maximum velocity possibly obtainable); eventually the force generated from friction and drag equals the maximum force of thrust that's possible. When this happens, the net force is 0, and there will be no acceleration, so the velocity can't increase, and will remain static. Given different elements of motion (mass, velocity, acceleration, change in position, etc) you can calculate unknown variables using the kinematic equations: Δx = 1/2 * a *t^2 + vi*t | Δv^2 = 2a(Δx) | Δv = a * t To relate kinematics to forces use Newton's second law: ΣF = m * a The following videos talk about the physics involved in a crash:
MomentumThe video on the left details an engineering choice that was implemented due to the nature of momentum. When you crash either into another car, or an inanimate object (such as a tree or a pole) an impulse is applied, which changes your car's momentum. Newer cars have material that can easily crumple, so if the car is in a crash, the crumpling absorbs some of the impact by increasing the time by which the force is applied, increasing the impulse. By doing this, the change in velocity of the impact is less sudden, and since the force is applied over a longer period of time, the passengers experience the sudden change in velocity slower; whatever whiplash they would feel is less extreme, lowering the chance of injury. Momentum can also be used to investigate crashes, since momentum is conserved in any collision. The video on the right details a crash report of an incident between a car and a truck driver. EnergyTo explain how energy affects driving, I will go over where the energy is stored during different stages of driving using LOL charts: In these LOL charts, Uc is chemical potential energy, Uk is kinetic energy, W is mechanical work, which in this case is friction and drag, and Q is heat lost. Heat (Q) is lost in 2 ways when driving. 1. when you convert chemical potential energy (gas) to kinetic energy, approximately 80% of the energy is lost through heat dissipation from the engine. 2. when you are braking (in the last LOL chart) heat is lost because when you push down on the brake petal, the brake pads press against the wheel's axle, causing a friction force to be applied between the rotating axle and the brake pad. This causes the kinetic energy to be converted heat energy and dissipate. Mechanical work is still done because of friction and drag. TurningWhile driving, turning is all about centripetal motion, or motion acting about a circular path. Every turn is essentially traveling along the arc of a circle. If you make a 90 degree turn, then you travel approximately 1/4th the arc of a circle. When turning there is a chance that your car will skid out of control. This happens if the centripetal force acting on your car is greater than the friction force acting between your tires and the road. You can calculate the Fc with the equation (m*v^2)/r. This is why to minimize the chance of skidding, one should drive slower, and make a wider turn, since centripetal force is quadratically proportional to velocity and inversely proportional to the radius. Furthermore, the chance of skidding increases on an icy road because the frictional force is lower between the road and the tires. Rotation and TorqueSince driving consists of your wheels rotating, rotational motion is involved. When the internal combustion engine generates its explosions from burning fuel, it pushes pistons, which turns the crank shaft in a rotatory motion. This rotates the wheels. If a car has more torque, then its wheels can rotate faster, and the car can in turn get more speed.
Below is a picture of the intersection before and after some road construction to make this intersection safer. This will be especially safer during the winter time when road conditions may be icy. The picture on the left with the red semicircle shows the intersection before the change and the picture on the right with the green semicircle after the change was made. The change increased the radius of the turn on the intersection Important equation to evaluate this situation: Centripetal Force = (Mass * Velocity^2)/Radius – Fc = (m*v^2)/r Evaluating the first equation, you can see that the radius of the turn and the centripetal force needed to complete the turn are inversely proportional. This means that if you increase the radius, less centripetal force is needed to complete the turn (and vice versa). For a car to skid, the tires need to lose traction with the road, and for that to happen the centripetal force needs to be greater than the frictional force between the tires and the road. Therefore, having the radius be smaller increases the Fc, and by extension, the chance of skidding. This is especially prevalent during winter because the frictional force between the road and the tires is less when there's ice on the road, so having a lower Centripetal force (from a higher radius) is important to reduce possible skidding. In conclusion, the radius being increased lowers the centripetal force needed to make the turn, and with icy roads, is necessary to lower the chance of skidding.
Going into the first test I knew from the practice test I took the day before that I would see a curveball or two that I wouldn't know how to handle. Those problems are the ones that scare me because there is very little I can do to prepare for them. Other than that I wasn't very worried for the test. I feel as though I conceptually understand the material pretty well. Taking Calculus is definitely an advantage when it comes to understand position, velocity, and acceleration time graphs, and the knowledge that I had a (however slight) advantage over my classmates was comforting. When I was taking the test I felt confident on how I did other than 2 of the multiple choice questions. I won't go into specifics, but they were "curveballs" and I wasn't entirely prepared to answer them. I didn't study very much for the test because I knew how to do the basic stuff (thanks to the mastering physics assignments), and knew that my main problem would be the problems I couldn't prepare for. In conclusion, I hope there's a curve.
I've been told by many people who have taken AP Physics in the past that it is a pretty big time commitment. While so far most of the material has been review, it still takes a long time. I do think that taking physics is important to any of the field I am planning on going into. Regarding the difficulty of AP Physics, I am more worried about the time commitment rather than the actual material. In the past I haven't spent much time on classes for homework every night nor have I gone into see a teacher on a regular basis. I feel as though this pattern will change from taking this class. Physics was the only science I enjoyed taking from the 3 core sciences you learn in high school. While chemistry and biology revolve around memorization, physics is more intuitive, which I find much more engaging. For this class I will need focus more and manage my time more than I have in the past, but I think in the end it will be for the better.
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