Here are two identical rope ladders with slanting rungs. One falls to the floor, the other onto a table. The ladders are released at the same time and fall freely, but the one on the left falls faster, as if the table is “sucking” it downward. Why does this happen?
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Consider a single pencil falling at a shallow angle. When one end strikes the table, the opposite end jerks downward. In the ladder this action tugs downward on the string above, accelerating its descent. The other ladder doesn’t experience these tugs (yet), so it falls more slowly.
(Anoop Grewal, Philip Johnson, and Andy Ruina, “A Chain That Accelerates, Rather Than Slows, Due to Collisions: How Compression Can Cause Tension,” American Journal of Physics 79:7 [July 2011], 723.)
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