Logical Reasoning

PT102 · S3 · Q19 When an ordinary piece of steel

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When an ordinary piece of steel is put under pressure, the steel compresses; that is, its volume slightly decreases.

Setup

(Unlike steel) when you put glass under pressure, the volume stays the same because glass is a fluid, so it flows to areas under less pressure.

The Blank

If you have a horizontal sheet of glass of uniform thickness and you put a really heavy object in the middle of it, then assuming the glass can support the the weight without cracking, the sheet of glass will eventually ______ .

Evaluate

We need to use the information we were provided about how glass behaves when it's put under pressure, to fill in this blank about what will happen when we put a horizontal sheet of glass under pressure by putting a heavy object in the middle of it.

We were told that when glass is put under pressure, the fluid glass will flow very slowly from areas under sustained pressure to areas under less pressure.

If we put a heavy object in the center of a sheet of glass, then the center will be under sustained pressure, while areas way from the center (like the four corners, for example) will be under less pressure.

So we know that the fluid glass will flow very slowly away from the center of the sheet of glass.

Goal

The blank is saying that eventually (this is accounting for the very slow flow of glass) ... what will happen?

Eventually, the fluid underneath the heavy object will flow away from the center to areas under less pressure.

19.

Which one of the following most logically completes the argument?

  1. become larger in size yet

    Contradicted

    Becoming larger in size would mean that the volume had increased. But we were told that glass's "volume remains unchanged" when put under pressure.

    6% picked this

  2. flow toward the point at

    Contradicted

    We were told that "any portion of glass under pressure will very slowly flow to areas under less pressure." So we would expect the glass will flow toward the point at which the pressure is least.

    9% picked this

  3. compress, although not as much

    Contradicted

    This answer is saying that the sheet of glass would compress. The second sentence says that, "Glass, however, is a fluid, so rather than compressing, it does [something else]."

    1% picked this

  4. divide into exactly two pieces

    Out of Scope

    Out of Scope: divide Too Strong: exactly two pieces We're talking about glass that can support the weight without cracking, so this paragraph doesn't seem to be leading into glass dividing/cracking into two pieces.

    3% picked this

  5. Correct

    be thinner in the portion

    Why this is right

    This answer feels like a bit of a stretch, but it helps us that the first four answers were pretty much contradicted. That would make anything non-contradictory be the most logical completion. We were looking for the idea that the flow of glass would move away from the center toward the areas under less pressure. Would this cause the glass under the heavy object to be thinner and the other parts thicker? Sure, since the glass started out at uniform thickness and now we're moving material away from the center to other areas. Picture one of those floating rafts people lay on in swimming pools, a rectangular shape with uniform thickness. If you put that raft on the sidewalk and then sat in the middle, your butt would sink down close to the sidewalk, while the headrest and footrest of the raft would puff up. That's because our butt pressure is sending the air from the area under sustained pressure to the areas under less pressure. That's the same phenomenon this answer choice is describing, in relation to a sheet of glass.

    Skill tested: Most Supported · how this choice captures the argument's function is the move to repeat next time.

    81% picked this

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