Unit 6 was one of my favorite units so far this year. We learned about work, potential energy, kinetic energy, and many other things. First I’m going to talk about work, work=forcexdistance. The proper definition is; the product of a force and distance moved by the force. One thing to know is that in order for something to be doing work on an object the force and distance must be parallel. In other words, if you are carrying a 10 Newton book and walking a distance of 20 meters you are doing no work on the book. But if you push the book along the ground you will be doing 200 Joules of work (Joules is the standard measure for work). While talking about work we must talk about power, power=work done/time interval. Basically, the amount of time in which work is done, power is measured in watts.
Next came energy, which is defined as the property of a system that allows it to do work. We talked about potential and kinetic energy. Potential energy is present the energy that an object possesses because of its position. When an object has potential energy it is at rest, the equation for potential energy is PE= mass x gravity x height. The next type is kinetic energy, which is the energy of motion. The equation is KE= ½ Mass x velocity squared. A roller coaster is a good example of both because, the first hill is always the largest in order to get the most potential energy so when transferred to kinetic energy there will be enough to make it up the next hill.
The work energy theorem states that the work done on an object equals the change I kinetic energy (change in KE = work).
Machines were the last thing that we talked about. A machine is a device used to increase or decrease the force you need to put in, in order to do a certain amount of work. One thing that is important when dealing with machines is the Law of Conservation of Energy, meaning that the work you put in equals the work put out (forcexdistance in = forcexdistance out). A machine lessens the force you need to put in to do this work by increasing the distance, therefore making your job easier. For example, when using a jack you only have to apply a little bit of force, but you must pump it a lot to only make the car move up a little (you increased the distance). A jack is a type of lever. The last thing you must know when dealing with machines is efficiency, or work output/work input. If a machine is 100% efficient that means that all of the energy was transferred and none was released. Efficiency is basically the percentage of energy you got out of what you put in.
One thing that was difficult for me to understand at first was the idea that machines don’t change the amount of work you do. I felt as though machines made it to where you needed to do less work on an object and that’s why they made things easier. However, as I explained above they actually increase the distance, which decreases the force, thus making it easier to do the work. Problem solving was a big part of this section because all of the equations were related. We were presented with questions that gave us a mass of an object, the speed at which is was travelling, the speed it sped up to, and the distance it traveled. Then the questions had several parts. First we had to find the change in kinetic energy. Then the work done, which you had to know equals the change in kinetic energy. Next the amount of force applied, which you had to know the distance travelled and the work done, so you could use the work formula. Lastly, you were given a time in which this work occurred and you had to find the power. So, it was crucial that we had a solid understanding of how these formulas related. These concepts apply to real life for me, because they really helped me learn why things like jacks and pulleys work so effectively and how I could use this knowledge in the future to move heavy objects.
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