Reading Comprehension

PT143 · S2 · P4 · Q21 The Myth of Liquid Glass

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To glass researchers it seems somewhat strange that many people throughout the world share the persistent belief that window glass flows slowly downward like a very viscous liquid.

Topic

The myth that old window glass flows downward over time, and the science debunking it.

Framework

Challenge Position

Main Point

The commonly held belief that window glass flows downward over time (causing old windows to be thicker at the bottom) is a myth; scientific calculations and historical glassmaking techniques explain the thickness differences instead. (The main point is most directly addressed at the beginning of paragraph 2 and fully explained in the last paragraph.)

P1: Introduction to the Glass Flow Myth

A lot of people (even in science books) mistakenly believe that window glass is a super slow-moving liquid and gradually flows downward, explaining the thicker bottoms in old windows. This myth likely started because glass's atoms are not arranged like in crystals, but the structure alone doesn't mean glass is liquid—it's solid at room temperature, just with a unique atomic arrangement.

P2: Scientific Debunking

A recent study shows that, although glass *can* flow under gravity, it would take longer than the age of the universe for old windows to change thickness from flow. So, that's not the reason old windows are thicker at the bottom!

P3: Why Flow Still Isn’t the Answer

Even the easiest-flowing glass (like germanium oxide glass) would still take trillions of years to change shape noticeably, and medieval glass—even with impurities—wouldn't flow in just a few centuries. The science is clear: for glass to flow, it actually needs to be heated to at least 350°C.

21.

Which one of the following most accurately states the main point of the passage?

  1. Zanotto's research has proven that

    Too Narrow

    This is a derivable claim from the end of the 2nd paragraph, but it doesn't have any of the big picture framing ideas. Where's the Challenge Position part? It doesn't address the popular belief that glass flows downward. Where's the Answer a Question part? It doesn't address the real reason that medieval cathedral glass bulges at the bottom (old glass-making techniques).

    1% picked this

  2. The technology of window-glass production

    Wrong Emphasis: technology

    This answer's main clause is, "The technology of window-glass production has progressed substantially". Did the author write this passage to update the world on window-glass production technology? Heavens, no. She wrote it to go after the misconception that glass flows downward. The author was helping people let go of their misconception by telling them the real reason that old glass bulges at the bottom is because of the old school janky technology.

    2% picked this

  3. After years of investigation motivated

    Wrong Emphasis: calculating flow rates

    The main clause here is, "Scientists have developed ways of precisely calculating even slow rates of flow in solids such as glass". Did the author write this passage in order to alert the world that science has gotten better at calculating the flow rates of solids? Heck no. She wrote it to address the misconception that glass flows downward, to present a study debunking that idea, and to supply the real causal story behind the misconception. The phrase "such as glass" in this answer makes it seem like glass was just one of potentially many examples of solids we were considering. Meanwhile, we know that glass wasn't an aside or an example. It was the central topic of the whole passage.

    4% picked this

  4. Recent research provides evidence that

    Opposite

    This answer is conceding that solid glass does flow slightly downward. That flow is part of why there is a noticeable difference in thickness between the top and bottom of old windows. This answer choice makes the passage out to be saying, "People think that old glass is thicker at the bottom because glass flows downward, and while that's true, there are other factors that also contribute." The passage is actually saying, "People think old glass is thicker at the bottom because glass flows downward, but they're believing a myth. Scientists think it's weird how people insist on believing this. Luckily, a new study empirically debunks this myth. It would take trillions of years for the flow of glass to make any noticeable change in thickness, and these old windows are less than 1,000 years old." The last sentence begins, "The difference in thickness in antique windows probably results instead from glass manufacturing methods". This answer is acting like it said, "... probably results in addition from glass manufacturing methods".

    8% picked this

  5. Correct

    Contrary to a commonly held

    Why this is right

    The main clause here is the Challenge Position part of the passage: differences in thickness are not due to the flowing of solid glass. The final clause captures the Answer a Question final paragraph: the real reason for old glass's weird thickness is glass manufacturing methods.

    Skill tested: Main Point · how this choice captures the passage's function is the move to repeat next time.

    85% picked this

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