Why do astronauts aboard the International Space Station seem to float? The ISS is only about 200 miles above Earth—where, according to Newton, gravity is almost as strong as it is here on the ground.

Stan Pearson, Newport News, Virginia

They experience weightlessness not because of a lack of gravity but because the ISS, and they, are orbiting Earth in constant free fall, says Valerie Neal, curator of space history at the National Air and Space Museum. They’re falling toward Earth and moving forward at about the same velocity. Because the downward and forward forces are nearly equal, the astronauts are not pulled in any specific direction, so they float.

Did the colonists really mount a massive chain across the Hudson River during the American Revolution? The required engineering skill and smithing manpower would seem beyond them.

Jono Mainelli, New York City

They really did. In 1778, the colonists, who then produced 14 percent of the world’s iron, forged the Great Chain to prevent a Royal Navy invasion upriver, says David Miller III, associate curator at the National Museum of American History. The chain consisted of 750 links, each two feet long and weighing more than 100 pounds. Soldiers stretched the iron barrier, supported by log rafts, across the river at West Point. They removed it in winter, to keep it from being broken up by river ice, and replaced it in spring throughout the war.

It’s generally known that a female honeybee’s stinger will rip away after stinging, fatally for the bee. Why would natural selection favor such a defense mechanism?

Michael Nieters, Des Moines, Iowa

This defense works for the colony, if not for the individual: Those females, worker bees, cannot reproduce, but their self-sacrifice defends the egg-laying queen. Also, says David Roubik, an entomologist at the Smithsonian Tropical Research Institute in Panama, the parting of bee and stinger exposes a gland that releases a pheromone alerting other colony members to sting the victim at that spot.

How did “wink” become a unit of sleep, as in “didn’t sleep a wink” or “40 winks”?

Daniel Beltz, Rochester Hills, Michigan

To “wink” meant to close one’s eyes for sleep as early as the 14th century, says Ives Goddard, senior linguist at the National Museum of Natural History. But “40 winks” as a synonym for “nap” didn’t appear until the 19th century, according to the Oxford English Dictionary. How that idiom evolved is a matter of speculation.

Methane decays rapidly in sunlight, so why or how is it a greenhouse gas?

Gary N. Miller, Davenport, Florida

That decay is relatively rapid; methane still lasts about eight years in the atmosphere. And like every other greenhouse gas, it traps heat in the atmosphere by absorbing infrared radiation, says Patrick Megonigal, deputy director of the Smithsonian Environmental Research Center. In fact, methane is about 30 times more efficient than carbon dioxide as an infrared absorber.

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