ShmoopTube

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Here's your shmoop du jour, brought to you by the Grand Canyon.

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Almost as awe-inspiring as AP Physics.

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Max is scolded by his parents for leaning over the railing of a dangerous vista at the Grand Canyon.

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Mom conveys her distress as she steps back from the ledge,

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and Dad cries out while lunging forward to grab his son. 

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Which of the following is technically true for Max

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as he stands still at the edge of oblivion?

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You know... other than the fact that he now has proof his parents love him?

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And here are the potential answers...

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This problem doesn't have a lot of numbers, so it's clearly a conceptual one.

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Heck, there are no numbers at all. If we glance at the answers,

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we'll see that they all have to do with the perceived pitch of Max's parents' cries.

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Also, the problem give us information on the motion of his parents.

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When we have waves and movement, our mind should immediately snap to the Doppler effect.

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Named for Christian Doppler, it's the phenomenon that occurs when a source of waves is in motion.

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Say, for example, that we had a speaker emitting a tone with a frequency of 100hertz.

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A listener 1 meter away would hear a frequency of 100 hertz.

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A listener 2 meters away would hear the same frequency.

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No matter how far, the sound is still 100 hertz.

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But, uh... what the heck is a hertz?

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A hertz is a measurement of one cycle of sound per second.

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One hertz every second the sound wave oscillates - moves up and down - one time.

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If a sound has a frequency of 100 hertz, it oscillates 100 times in a second.

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This rate of oscillation determines how high or low a sound is.

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A higher frequency means a higher sound.

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What if the speaker starts moving?

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If the speaker moves away from the listeners, then the distance between each wave would increase.

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This decreases the frequency and creates a lower tone.

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On the other hand, if the speaker moves toward the listeners,

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the waves would become closer together, and a higher tone would be heard.

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So Max's father moving toward him will sound higher, and his mother will sound lower.

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The only answer that fits this description is (D).

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Next year's family vacation?

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Kansas.

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