Question: “If you made a beach using grains the proportionate size of the stars in the Milky Way, what would that beach look like?” (74).

Typical grains of sand range from 0.2 to 0.5 millimeters, but the range of star sizes is far wider. If the Sun were a typical grain of sand, then the beach would be a large field of stones, gravel, and boulders with just a small patch of sand. This sand patch would hold 99% of the grains but only 1% of the beach’s total volume.

Question: “How tall can a swing set be while still being powered by a human pumping their legs? Is it possible to build a swing set tall enough to launch the rider into space if they jump at the right time?” (79).

Pumping one’s legs, or “driven oscillation,” works by pushing around the pivot of the crossbar. Pumping becomes less efficient as the swing set becomes taller because each pump adds less twist to the whole system, while air resistance becomes more significant. The ideal swing to propel by pumping is 10-15 feet tall, which is the height of a normal playground swing set.