In the first paragraph, it is written "the smaller the frequency." Usually, when talking about frequencies, you don't say smaller and larger. Those typically refer to amplitude (volume) of a sound wave. Because frequency is related to pitch, I would write "the lower the frequency." I know it is your hypothesis, so it's okay to have a hypothesis that is unsupported. That is what you have, because adding water to the glasses will make the pitch higher.
The third paragraph feels different. The opening two paragraphs established a tone and feel to your writing style (especially the first paragraph). Paragraph three (and a few that follow) is a distinct break in that voice. That paragraph, due to the vocabulary in it, feels like much of it was copy and pasted from your source. I'm glad to see that you cited your source, but if any of it is word for word quotations, you need to put quotation marks around those areas. Then the reader knows why the paragraph's "voice" sounds so different. The quoting suggestion needs to be applied to each paragraph.
Fourth paragraph: ". . . with it, producing a wave of water visible close to the edge of the glass. When those waves a produced . . ." Change to "producing a visible wave of water close to the edge of the glass. When those waves are produced . . . "
The 5th paragraph mentions an "effective increase in mass and decrease in energy." You might want to explain exactly how that happens. A change in mass within a closed system (glass and water) should not happen. Explain why it is an "effective" change.
6th paragraph talks about standing waves and superposition. I would avoid using "superposition," since it is typically synonymous with quantum mechanics at the atomic level. The wave interaction in your glass is not being tested at the atomic level. A standing wave is created by the wave interaction of interference. Your explanation of constructive and destructive are types of interference and were explained well. Note: Standing waves have total destructive interference at specific nodes.
Overall, the introduction is good. It made sense to me, and I teach science. If your audience is not a "science person," you might want to reduce the cognitive overhead (dumb it down) for your reader. In some places that means using an easier vocabulary word. In other places it means writing more to better explain a process. Your stick and slip paragraph is a good example of a well explained process. A layman could understand that no problem. There are a few grammar/flow issues scattered around. Nothing major but it is very difficult to highlight them using this Enotes interface. The best way for you to find and fix them is to read the introduction to yourself . . . out loud. That will force you to pay attention to each word and hear how it reads. I use that method all the time. It just works. Again, nice work so far.