Second Semester Unit 2 Blog Reflection

It's hard to believe that another unit has gone by this semester and it is only February. Our units have been so short that they just fly by. This unit has seemed particularly easy, but I guess we will see how easy it was tomorrow during the test. Not only did we learn about work and power but also their relationship together. We also learned about kinetic energy, potential energy,the change in kinetic energy, the law of the conservation of energy, and machines. To start things off, lets talk about work. Work means that you are exerting a force on an object over some distance. It is equal to force multiplied by distance. Work is measured in joules which is one Newton-meter. We learned that there is a specific relationship between the force and the distance; these items need to be parallel to one another for work to be done. For example, when a waiter is carrying a tray and walking, he is not doing work because his force and distance are not parallel to one another. Also, you have to be moving some distance to be doing work. When you push against a wall, you are not doing work on a wall. However, your muscles are doing work because they are stretching and moving over a distance. You are still exerting a force on the wall, but since the wall doesn't move (or shouldn't move because maybe sometimes it does move) you are not doing work on that wall. Moving on, the next thing we talked about was power. Power is how quickly work is done. It is equal to work divided by time. We measure power in watts which is one joule/second. Here, we also talked about horsepower, which is how much work something does. One horsepower is equivalent to 746 watts. That's impressive! Work and power have a special relationship with each other. Think back to when we did the experiment running and walking up the steps. When we calculated the work for both running up the stairs and walking up the stairs, they stayed exactly the same. This is because neither the force or distance were changed. Work does not depend on time. However, power does. The answers for the power when running and walking up the stairs were very different to each other. Because it took a longer amount of time to walk up the stairs, there was less power done. Accordingly, running up the steps took a lot less time which meant there would be more power. This concept can be complicated to grasp at first, but once you think about it a few times it starts to sink in. Next, we talked about kinetic energy, potential energy, and the change in kinetic energy. We know that kinetic energy is the energy of motion. The equation for this is one half of the mass multiplied by the velocity squared. To calculate the change in kinetic energy you calculate the initial kinetic energy and subtract that from the final kinetic energy. The change in kinetic energy is equal to work. Potential energy is stored energy. To calculate the potential energy, you multiply the mass, the gravity, and the height together. Then, we learned about the law of the conservation of energy. This law states that energy cannot be created or destroyed. It may however be transformed from one form into another, but the total amount of energy never changes. We talked about how in cars, energy is transformed into heat, and that is why an engine heats up. We also talked about this in terms of a ball falling to the ground. Before the ball has started movement, it might have 1000 Newtons of potential energy and zero Newtons of kinetic energy. Then, as the ball reaches the halfway mark, it will have 500 Newtons of potential energy and 500 Newtons of kinetic energy. Then, right before the ball reaches the ground, it will have zero Newtons of potential energy and 1000 Newtons of kinetic energy. The amount of energy will be constant throughout the fall. Finally, we learned about machines. A machine helps decrease the force needed to exert on an object and still keeps the work the same amount. There are two different kinds of work here, the work in and the work out. While both of these final values will be the same, there is still a difference between the two. The work in has a larger distance which results in a smaller force whereas the work out has a smaller distance resulting in a larger force. One machine is an inclined plane or ramps. These ramps help use energy more effectively. There are many other kinds of machines that we use in our every day lives and just might not know it. I feel that unit has gone particularly well. I still think that my confidence in solving physics problems is increasing. One thing I have not done that much in this unit is talk in class. I think that I could benefit from doing this more. Similarly, I have also been thinking of different methods of studying for tests to improve my grades each time. I have been working on a study guide that has all the concepts we studies this unit. It seems to be working well since I feel confident about this material but we will see tomorrow come test time.