Readers ask about buoyancy, Stonehenge sounds and more

Readers ask about buoyancy, Stonehenge sounds and more

cover of the September 26, 2020 issue

Rock the boat

Scientists made a toy boat float upside down on the bottom of a layer of levitating liquid, Maria Temming reported in “Toy boats defy gravity by floating upside down” (SN: 9/26/20, p. 32).

“I was quite intrigued by the upside-down boat. The explanation of buoyancy versus gravity does suggest an equilibrium for the upside-down boat, but it seems to be unstable in theory,” reader David Edmonston wrote. “If the upside-down boat were pushed upward ever so slightly, then its buoyancy should increase, making the boat rise to the top of the liquid layer,” Edmonston wrote. “If it were pushed downward, then its buoyancy should decrease, allowing it to fall below the underside of the levitated liquid. That would be an unstable equilibrium, like standing a pencil on its point. Is there more to the explanation? Is there surface tension involved? Upward force from the levitation?” he asked.

The boat does exist in an unstable equilibrium, Temming says. “Shaking the container holding the boat and liquid helps the upside-down boat maintain a steady position on the bottom of the liquid layer,” she says. “Because the boat is constantly shaking up and down as well, its own vertical vibrations cancel out any external jostling that would knock the boat off its float. More massive boats require stronger shaking to resist being knocked down to the bottom of the container or up to the top of the liquid layer.”

Spooky sound effects

A scale model of Stonehenge revealed that the complete structure would have amplified speech and improved musical sounds for people inside it, Bruce Bower reported in “Stonehenge enhanced sounds within” (SN: 9/26/20, p. 14).

“I’ve always found Stonehenge very interesting. It is in the middle of fields, but a busy road passes it about a half a mile or so away.… You get a weird thrill seeing it loom up out of the mist as you drive along,” reader Michelle Reeve wrote. “Another weird acoustic effect is that although the road is visible from the monument … strangely you cannot hear the traffic. Sound normally carries well over open ground,” Reeve wrote. “It gives the impression of a ghost road from another dimension. A spooky effect!”

Energy matters

Spacetime ripples revealed that two black holes merged to form the first definitive example of a midsize black hole, Emily Conover reported in “Midsize black holes really do exist” (SN: 9/26/20, p. 7).

Eight solar masses’ worth of energy was carried away by gravitational waves during the merger. Reader Jonathan Lis wondered if matter was converted into that energy.

Matter particles aren’t being converted into energy in this case, Conover says. Instead, other forms of energy are transformed into the gravitational wave energy. “The orbiting black holes have both kinetic and potential energy. It’s that energy that gets converted into gravitational waves,” she says. Because energy and mass are equivalent in general relativity, that means the total mass of the system decreases when the black holes merge.

Life story

Clumps of bacteria exposed to the harsh conditions of outer space might be able to weather a trip between Earth and Mars, Jonathan Lambert reported in “Bacteria can survive for years in space” (SN: 9/26/20, p. 10).

Reader Daniel Jameson wondered if such floating clumps of microbes could have seeded early Earth with life.

That idea is one of many theories for how life on Earth began, Lambert says. While there’s no direct evidence that life descended from otherworldly microbes, amino acids and sugars have been found in outer space and within meteorites on Earth. That suggests space rocks could have delivered those and other necessary ingredients for life to the planet. Another theory is that early Earth formed the ingredients, and eventually life, on its own (SN: 9/26/20, p. 22).

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