Logical Reasoning

PT156 · S2 · Q19 Geologist: As a spinning object's radius

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Geologist: As a spinning object's radius decreases, its rate of rotation increases; for example, figure skaters can twirl faster by bringing their arms closer to their sides.

Conclusion

The law that a spinning object speeds up as its radius shrinks helps explain why Earth's rotation rate increased over the past decade.

Evidence (For, and, since)

A spinning object rotates faster as its radius decreases, as figure skaters show by pulling in their arms.

Earthquakes increased in number and severity during the past decade.

Immediately after an earthquake, tectonic plates move toward Earth's center, which decreases Earth's radius.

Evaluate

The #1 pattern on Strengthen / Weaken is Explain Curious Fact.

The CURIOUS FACT we're trying to solve: How come Earth's rate of rotation has increased over the past decade?

The author's EXPLANATION: after a quake, the tectonic plates move toward the center of the Earth, which causes Earth's radius to decrease, which causes the rate of rotation to increase.

A correct answer would either offer an Alternate Explanation for the curious fact, or it would hurt the plausibility of the story the author is telling.

Goal

Look for an answer offering a different reason why Earth's rotation would be speeding up, or an answer making it seem like the decreasing radius of the Earth following an earthquake wouldn't be the cause of Earth's rotation speeding up.

19.

Which one of the following, if true, would most undermine the geologist's explanation of why Earth's rate of rotation increased over the last decade?

  1. In the beginning of the

    Opposite (if anything)

    This strengthens the plausibility of the author's story, since it is more evidence that Cause / Effect have coincided. The author thinks that a decreasing radius is causing more quakes, and this is giving a historical example to corroborate that theory.

    2% picked this

  2. Correct

    During the past decade, other

    Why this is right

    This weakens by ruining the plausibility of the author's story. He wanted us to think that the reason we've had faster rotation the past decade is because we've had more quakes, which lead to a decreased radius, which leads to faster rotation. This is basically saying, "No, in the last decade, quakes wouldn't have led to a decreased radius, because other events counteracted the movements of the plates". It's a frustratingly vague answer. Did the other geological events prevent the the tectonic plates from moving? I think that's what they're going for by saying it "counteracted the movements that occur after quakes". Is that contradicting a premise? Yeah, kind of. But remember, there's no rule against that. That happens sometimes. If the plates don't move, then the radius doesn't decrease, and so this wouldn't be the explanation for why Earth's rotation has increased.

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

    89% picked this

  3. Only skillful figure skaters succeed

    No Impact

    Wow, leave the skaters alone, (C). They are a total afterthought to this argument. We don't care that skillful skaters can do this "shrink your radius, spin faster" move while unskilled skaters can't pull it off. The skaters are an illustration of the law, not evidence for it. The physical law still exists that as a spinning object's radius decreases, the rotation speed increases.

    1% picked this

  4. Since the time of the

    No Impact

    Strengthen and Weaken are famous for having these wishy-washy wrong answers that just say, "Things change / differences exist". Ok, the rate of fluctuation has been known to change over time. That doesn't in any way help us solve the causal mystery of why the rate increased in the past ten years. If this answer were saying, "the rotation just naturally speeds up for a while then slows down for a while", then it could be an alternate explanation, but this isn't saying that the rate naturally ebbs and flows as part of some cycle. It's just saying we've been able to measure this sort of difference for the last 3000+ years.

    5% picked this

  5. Increased volcanic activity over the

    Unclear Impact

    More plate movement overall could mean more inward movement, which would support the geologist, or more movement in other directions, which might not. Without knowing which way the plates moved (or whether any of that movement shrunk the radius of the Earth), we don't know how this answer impacts the argument.

    2% picked this

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