Signs of life

Q: Would ancient features on a lifeless planet like Mars (if indeed it lacks life) become covered with meters of material, as we know happens on Earth with ancient cities and even natural features? Or is a carbon cycle required for the scale of the process we see on Earth?

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FROM THE MAY ISSUE:We asked you to complete a children’s cartoon script about why the air molecule Bob would travel faster over an aircraft wing than the molecule Flo traveling under it. Your responses were reviewed by Haithem Taha of the University of California, Berkeley.

WINNER: Flo: “I heard it was because of a law from Dr. Bernoulli.”

Bob: “But Flo, why would I fly faster just because I have to go farther? That would be like saying when we’ll ride our bikes to school, you take the shortcut and I’ll take the long way, and we’ll get there at the same time because I will pedal faster. But there’s no reason why I should pedal faster other than to force the result to get to school when you do. My uncle, Klaus Weltner, told me that it is pressure difference that causes us air molecules to move. You will be compressed against our other friends on the lower side of the wing, which creates a force that helps lift the airplane. It’s like when we put our hands out the window of a moving car. When we tilt them at a little angle, they are lifted up. But behind me, on my side of the wing, there is going to be less pressure on the shielded upper side of the tilted surface. So I will actually be forced to move faster because I will be subject to a greater pressure difference along the wing than you. I’m afraid I may not meet you again at the end of the wing, Flo. That’s not a requirement that Uncle Klaus said can be guaranteed. But I will look for you with our other air molecule friends in the calming of our motions caused by this passing wing.”

Jeffrey Cerro, AIAA Associate Fellow

Poquoson, Virginia

Jeffrey retired last year from NASA’s Langley Research Center in Virginia, where he worked in the Vehicle Analysis Branch as a structures and mass properties engineer.

Haithem Taha would add this response from Flo: “As you know, Bob, we air molecules don’t like to curve much. It’s called the principle of minimum curvature due to Hertz. But the wing is curved, so we will have to figure out a way to flow around it without curving more than necessary. We’ll create a circulation around the wing that makes you go faster. Otherwise, I and our friends traveling below the wing will have to rotate around the sharp trailing edge; I’m not sure we’ll be able to sustain this much curvature, Bob.”

Signs of life