Ch6_WangS

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 * Work, Energy, and Power**

a) Work

 * 1) ====__Definition and Mathematics of Work (method 3)__====
 * What is work?
 * Work is when an object is displaced due to a force acting on it.
 * How can this be shown mathematically?
 * Work is equal to the net force times the displacement times cosine of theta. When there is a 90 degree angle between the force and displacement vectors, there isn't work.
 * Under what circumstances does work occur?
 * For work to occur, the force must result in displacement. However, even if there is displacement, work may not have occurred. It only occurred if the force caused the motion, not the other way around.
 * What is negative work?
 * When the force vectors and the displacement are in opposite directions, the force is preventing the displacement. This causes negative work.
 * What unit is work measured in?
 * Joule. It is equal to 1 Newton * 1 meter
 * Theme: There are three things that you have to know to calculate work, which is when a force acts upon an object to cause a displacement, and those three things are: force, displacement and the angle between the force and the displacement.

a) Internal vs. External Forces

 * What forces are considered internal forces?
 * Examples of internal forces include gravity forces, magnetic force, electrical force, and spring force.
 * What forces are considered external forces?
 * Examples of external forces include applied force, normal force, tension force, friction force, and air resistance force.
 * What is the difference between positive work and negative force?
 * If there is positive work, then the object gains energy, and if there is negative work, then the object loses energy.
 * Describe internal work.
 * If net work is done on an object by an internal force, the total mechanical energy of that object stays the same. However, the object's energy changes form. Even though some kinetic energy can turn into potential energy, and vice versa, the sum of those will remain constant. Internal forces are sometimes called conservative forces.
 * Describe external work.
 * If net work is done on an object by an external force, the total mechanical energy of that object changes. It can either gain or lose potential energy, kinetic energy, or both. The work that is done is equal to the change in mechanical energy of the object. External forces are sometimes called nonconservative forces.
 * Theme: Internal forces change the form of energy, not the amount, while external forces change the amount of mechanical energy in an object.
 * Exercises: For the first part of the practice, where you have to say if the energy went from PE to KE or KE to PE, I got every one right. For the next section, I got all the "+ or - work" questions right, but I got a few "Change PE or KE or Both" questions wrong.

**Energy Bill Analysis**


The cost of electricity does seem like a lot to me. It is surprising how it costs so much money to run appliances, especially when a few items only cost a couple of cents a day in electricity. Even though the monthly total that I calculated was around $57, I use way more than 10 electronic appliances, and I know my sister and parents use a lot of electricity too. For example, I didn't account for our washing machine and clothes dryer, or our dishwasher. I also didn't account for the numerous lamps around the house. We also have more than 1 TV. I think the actual cost should be around $500 a month. Since I consume a lot of electricity, I should really cut down a bit. One thing I can do is try to use my computer less, and watch less TV. I can study or read instead. Also, I can let my hair air dry, instead of using a hair dryer. This is healthier for hair anyways. Something else I can do is turn off the lights and other electronics when I'm not using them.
 * Conclusion:**