For my waves blog I decided to explain the phenomenon that is the doppler effect. The doppler effect is when you observe a change in the pitch of a either an object moving by you or when you are moving by an object. This effect can be observed in the video clip below as my car drives past a camera at second 26. As the car approaches the camera the pitch of it raises and goes back down after the car passes. This is because as the car is traveling towards the waves in front of it causing them to be pushed together causing a higher frequency to be heard and the waves behind it are being driven away from so they are separated more causing a lower pitch to be heard.
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Like all motion track and field is following the laws of physics but once you understand these laws you can optimize how you work allowing you to go faster and have less injuries. Forces are very important to understanding track and field. The two images below show forces acting on a runner. These images highlight the forces that influence good running form. One mistake many people make when running is allowing their legs to go ahead of their body during their stride. But as can be seen in the second diagram you shouldn't do this as you are exerting a downward and forward force on the ground which because of newtons third law will then exert a upwards backwards force on your leg slowing you down and forcing you to exert more energy to maintain your speed. The first image shows that the ground reactionary force is actually made up of two forces, a normal and a friction force. Energy is also very important to running in track. The main conversion happening is from chemical potential energy from the food you have eaten to both kinetic energy and internal energy (heat). If you have not had anything to eat for a long time before a run you will likely not perform well as you will have less chemical energy to convert into kinetic energy to travel. When you are running in the cold and before you start running you are cold and need a sweatshirt but after you warm up no longer the sweatshirt is because internal energy is also created when the chemical energy is converted into kinetic energy. One last way energy is important in running is explaining why you speed up going down hills and slow down going up hills. At the top of a hill you have all of your kinetic and chemical energy along with more gravity potential energy than you will have at the bottom of the hill so this Gpe can be converted into kinetic energy. This transfer can be seen in the LOL chart below. The relationship is the opposite of this for going uphills. At the top of the hill you need to have more Gpe than you had at the bottom so your kinetic energy is converted into that so to maintain your speed you need to convert even more chemical energy to kinetic. One of the most common injuries in track is shin splints. While running does have some strong and repeated forces on your legs one of the biggest causes of this injury is stopping abruptly and if runners understood momentum they would realize why its bad to do this. Momentum is calculated by mass * velocity. So when a full grown runner is doing a 100 meter sprint traveling at about 9m/s and weighs about 70kg they have a momentum of 630kgm/s. The formula for change in momentum is Force * change in time. So if they wanted to slow down in one second they would need to exert 630N on their legs for 1 second which is an extremely large force and can lead to injury. If they even took just two seconds they would only be exerting 315N over those 2 seconds. So the longer they take to slow down the smaller the force exerted on their legs is reducing their chance of injury as they are changing their momentum over a longer period of time. One type of running form is called Chi running and calls for the runner to lean their body forward as they run and once the form is done well allows runners to travel faster. This can be explained by rotational motion. The point where your feet make contact is your fulcrum and your body up until your center of mass is the radius of the motion. So as you lean forward the Fg acting on you now has a component perpendicular to the radius which makes a torque pulling your body down but because this is rotational motion it is rotating around the fulcrum meaning there is also a horizontal component to the motion speeding up your running. In the video of somebody teaching chi running he has people try to lean at their hips and this doesn't produce the result that leaning the whole body does as the center of mass won't change as much.
Obviously running is also linked to motion, you're moving. You have to accelerate at the start of a race. You cannot reach a higher velocity without passing through all lower velocities before. There are countless other links to motion in this blog post as well.
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. Using your knowledge of physics that you have learned in class, explain why this right-hand turn was dangerous before the construction (especially during the winter). Then explain why it will be safer after the construction? This intersection was made safer by increasing the radius of the curve that the car travels on. Because centripetal force needed to stay on a circular path can be found with Fc=mv^2/r as radius increases the force needed will decrease. So previously the turn had a very tight turn and a small radius meaning lots of centripetal force was needed to not spin out. The force in this situation is friction so as the roads get icy it is harder for a car to have enough friction to not spin out. By increasing the radius of the turn much less centripetal friction force is needed to not spin out making the turn safer as it is more likely for a car to have enough force to continue on its circular path and not spin out during the turn.
I think the test went well and I felt mostly prepared. It seemed a little bit harder than the class test which was where most of my studying was because I felt very confident in that. So my review was doing all of the homework, making my content page, and the class test but besides that no specific studying. This had me feeling mostly prepared for the test except for a few questions where I had to guess on some of the details on how to solve them. But overall I think I did well on the test.
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AuthorCharles Stuart, Archives
April 2019
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