In the course of time, physics as a science underwent great changes. From a subdivision of philosophy it gradually turned into an applied science and then, in the 20th century, into an extremely complicated, greatly specialized and somewhat closed science. For the majority of this time physics has been rather ambiguously limited, describing the movements of celestial bodies and other material objects that stand behind the construction of many mechanisms and so on. To be a physicist was to know something about all these fields. But in the 20th century and, especially, after the works of Albert Einstein, everything changed. Physics split into a number of very narrow and very specialized fields, sometimes with little connection between each other. The majority of scientists work in one and the same field their entire lives.
Longer essays may also contain an introductory page that defines words and phrases of the essay's topic. Most academic institutions require that all substantial facts, quotations, and other porting material in an essay be referenced in a bibliography or works cited page at the end of the text. This scholarly convention helps others (whether teachers or fellow scholars) to understand the basis of facts and quotations the author uses to support the essay's argument and helps readers evaluate to what extent the argument is supported by evidence, and to evaluate the quality of that evidence. The academic essay tests the student's ability to present their thoughts in an organized way and is designed to test their intellectual capabilities.
Plan B: Use Plan B if you have only a few, larger similarities or differences. After your introduction, in the next paragraph discuss one similarity or difference in BOTH works or characters, and then move on in the next paragraph to the second similarity or difference in both, then the third, and so forth, until you're done. If you are doing both similarities and differences, juggle them on scrap paper so that in each part you put the less important first ("X and Y are both alike in their social positions . ."), followed by the more important ("but X is much more aware of the dangers of his position than is Y"). In this format, the comparing or contrasting goes on in EACH of the middle parts.