Why Does the Leaning Tower of Pisa Lean?

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In 1172, Donna Berta di Bernardo donated 60 silver coins to the local cathedral for the purchase of stones to be used in the base of a new bell tower.

The next year, construction on the tower began and almost immediately there were problems. The tower site sat on soft ground composed mostly of clay, fine sand, and shells (the city sits between the Arno and the Serchio rivers). By the time the builders finished the second floor in 1178, the tower was beginning to lean.

Soon, construction was halted for almost 100 years, as Pisa fought wars against Genoa, Lucca, and Florence. This may have been a lucky break, as modern analysis says that the tower definitely would have toppled had construction continued without time for the soil to settle.

When work on the tower resumed again, it was leaning 0.2 degrees north of vertical, but by the time the workers started on the seventh floor, the tower was tilting one degree south. Around this time, construction stopped again for unknown reasons.

DON'T LEAN ON ME

Over the next century, construction continued intermittently.

The tower’s lean gained another 1.6 degrees. To counteract the lean, the builders made the remaining floors taller on the south side of the tower. But the weight of the additional floors only made the foundation sink further, making the lean worse. Having done what they could, the builders finished up and officially completed the tower around 1370.

Since the tower’s completion, engineers and architects from all over the world have monitored the lean and tried to correct it. These attempts have involved adding grout to the foundation masonry, wrapping plastic-coated steel pieces around the tower up to the second floor, pouring a concrete ring around the base of the tower, laying lead counterweights to the north side, installing anchored cable counterweights, and extracting soil from underneath the north side.

After the removal of more than 70 metric tons of soil in 2008, engineers announced that the Tower had been stabilized enough that it had stopped moving for the first time since construction began. Its lean is now only about four degrees (prior to the all the restoration attempts, the lean was 5.5 degrees), or about 13 feet past perfectly vertical. The Leaning Tower of Pisa should be stable for at least the next 200 years.

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Do Lobsters Really Mate for Life?

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It's a pop culture trope that mated lobsters stay together until they die. But is it true?

Nope. While plenty of animals practice long-term monogamy, lobsters are not among them. Lobsters actually mate by a weird system of serial monogamy. It's not exactly a one-night stand, but it's not a lifelong commitment either. Instead, a bunch of females take turns having a fling with the local dominant male that lasts a week or two and, if they're not happy with the amount of genetic material he's provided, then seek a little extra action.

It works like this: A female lobster who's ready to mate (which they can only do right after they've molted) hangs out near the den of the local dominant male and fans her pheromone-laced urine into his home. This relaxes the male, making him less aggressive and more receptive to mating. Then there's a brief courtship, and the male allows the female into his den.

Anywhere from a few hours to a few days later, the female slips into something a little more comfortable by shedding her exoskeleton. (Shacking up with the neighborhood tough guy guarantees her protection during this vulnerable time.) The pair mates, and the male deposits his sperm in the female. Once her new shell has hardened a week or two later, she takes off, and another female can have her turn. Often, the females in an area will stagger the timing of their molts to make their reproductive conga line more efficient. As soon as one female is done with the stud, the next one is already waiting to pee on his doorstep.

Sometimes, the male doesn't provide enough sperm to fully fertilize all of a female's eggs. In these cases, she'll leave before her new shell finishes forming to find and mate with another male (or males) until she collects enough sperm. Usually this requires just an extra dalliance or two, but as many as 10 have been reported.

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Could an Astronaut Steal a Rocket and Lift Off, Without Mission Control?

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C Stuart Hardwick:

Not with any rocket that has ever thus far carried a person into orbit from Earth, no. Large rockets are complex, their launch facilities are complex, their trajectories are complex, and the production of their propellants is complex.

Let me give you one simple example:

  • Let’s say astro-Sally is the last woman on Earth, and is fully qualified to fly the Saturn-V.
  • Further, let’s say the Rapture (which as I understand it, is some sort of hip-hop induced global catastrophe that liquefies all the people) has left a Saturn-V sitting on the pad, raring to go.
  • Further, let’s grant that, given enough time, astro-Sally can locate sufficient documentation to operate the several dozen controls needed to pump the first stage propellant tanks full of kerosene.
  • Now what? Oxidizer, right? Wrong. First, she has to attend to the batteries, oxygen, hydrogen, and helium pressurant tanks in her spacecraft, otherwise it’s going to be a short, final flight. And she’ll need to fill the hypergolics for the spacecraft propulsion and maneuvering systems. If she screws that up, the rocket will explode with her crawling on it. If she gets a single drop of either of these on her skin or in her lungs, she’ll die.
  • But okay, maybe all the hypergolics were already loaded (not safe, but possible) and assume she manages to get the LOX, H2, and HE tanks ready without going Hindenburg all over the Cape.
  • And…let’s just say Hermione Granger comes back from the Rapture to work that obscure spell, propellantus preparum.
  • All set, right? Well, no. See, before any large rocket can lift off, the water quench system must be in operation. Lift off without it, and the sound pressure generated by the engines will bounce off the pad, cave in the first stage, and cause 36 stories of rocket to go “boom.”
  • So she searches the blockhouse and figures out how to turn on the water quench system, then hops in the director’s Tesla (why not?) and speeds out to the pad, jumps in the lift, starts up the gantry—and the water quench system runs out of water ... Where’d she think that water comes from? Fairies? No, it comes from a water tower—loaded with an ample supply for a couple of launch attempts. Then it must be refilled.

Now imagine how much harder this would all be with the FBI on your tail.

Can a rocket be built that’s simple enough and automated enough to be susceptible to theft? Sure. Have we done so? Nope. The Soyuz is probably the closest—being highly derived from an ICBM designed to be “easy” to launch, but even it’s really not very close.

This post originally appeared on Quora. Click here to view.

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