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# Can a Penny Dropped from a Skyscraper Kill Someone?

Let's just get this out of the way up top: No, a penny dropped from the Empire State Building cannot kill a pedestrian below. But the interesting question is why not?

The answer starts with terminal velocity. If we calculate the maximum speed a penny can achieve due to acceleration from gravity minus drag from wind on the 1,250-foot drop from the Empire State Building, we get a speed of perhaps 30-50 mph, depending on various assumptions made about wind, the orientation of the penny, and so on. In the clip below, the MythBusters start by shooting a penny at about 65 mph to test the highest conceivable speed a penny might achieve.

Where it gets interesting is sorting out just how much this would hurt. If somehow you were hit by a falling penny, would it break the skin? The MythBusters try this, and predictably scale up the test to the point where they're effectively shooting a penny like a bullet. At one point, Adam Savage takes a penny for the team...and lives.

Have a look, and keep an eye out for Savage's 2003-era haircut and earring. Enjoy:

Carl Court, Getty Images
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Is There a Limit to How Many Balls You Can Juggle?
Carl Court, Getty Images

In 2017, a juggler named Alex Barron broke a record when he tossed 14 balls into the air and caught them each once. The feat is fascinating to watch, and it becomes even more impressive once you understand the physics behind it.

As WIRED explains in a new video, juggling any more than 14 balls at once may be physically impossible. Researchers who study the limits of juggling have found that the success of a performance relies on a number of different components. Speed, a.k.a. the juggler's capacity to move their hands in time to catch each ball as it lands, is a big one, but it's not the most important factor.

What really determines how many balls one person can juggle is their accuracy. An accurate juggler knows how to keep their balls from colliding in midair and make them land within arm's reach. If they can't pull that off, their act falls apart in seconds.

Breaking a juggling world record isn't the same as breaking a record for sprinting or shot put. With each new ball that's added to the routine, jugglers need to toss higher and move their hands faster, which means their throws need to be significantly more accurate than what's needed with just one ball fewer. And skill and hours of practice aren't always enough; according to expert jugglers, the current world records were likely made possible by a decent amount of luck.

For a closer look at the physics of juggling, check out the video below.

Lawrence Livermore National Laboratory, Wikimedia Commons // CC BY-SA 3.0
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7 Giant Machines That Changed the World—And 1 That Might
Lawrence Livermore National Laboratory, Wikimedia Commons // CC BY-SA 3.0

From a 17-mile-long particle accelerator to a football-field–sized space observatory, here are seven massive machines that have made an equally huge impact on how we build, how we observe our universe, and how we lift rockets into space. We've also included a bonus machine: a technological marvel-to-be that may be just as influential once it's completed.

Carlo Fachini, Flickr // CC BY-ND 2.0

The Large Hadron Collider, a particle accelerator located at CERN outside of Geneva, Switzerland, is the largest machine in the world: It has a circumference of almost 17 miles and took around a decade to build. The tubes of the LHC are a vacuum; superconducting magnets guide and accelerate two high-energy particle beams, which are moving in opposite directions, to near-light-speed. When the beams collide, scientists use the data to find the answers to some of the most basic questions of physics and the laws that govern the universe we live in.

Since the LHC started up in 2008, scientists have made numerous groundbreaking discoveries, including finding the once-theoretical Higgs boson particle—a.k.a. the "God" particle—which helps give other particles mass. Scientists had been chasing the Higgs boson for five decades. The discovery illuminates the early development of the universe, including how particles gained mass after the Big Bang. Scientists are already working on the LHC's successor, which will be three times its size and seven times more powerful.

#### 2. CRAWLER-TRANSPORTER ROCKET MOVERS

Built in 1965, NASA's crawler-transporters are two of the largest vehicles ever constructed: They weigh 2400 tons each and burn 150 gallons of diesel per mile. In contrast, the average semi truck gets roughly 6.5 miles per gallon. The vehicles' first job was to move Saturn V rockets—which took us to the moon and measured 35 stories tall when fully constructed—from the massive Vehicle Assembly Building (the largest single-room building in the world) to the launch pad at Cape Canaveral. The 4.2-mile trip was a slow one; the transporters traveled at a rate of 1 mph to ensure the massive rockets didn't topple over. Without a vehicle to move rockets from the spot they were stacked to the launch pad, we never could have gotten off the ground, much less to the moon.

After our moon missions, the crawler-transporters were adapted to service the Space Shuttle program, and moved the shuttles from 1981 to 2003. Since the retirement of the orbiters, these long-serving machines are once again being repurposed to transport NASA's new Space Launch System (SLS), which, at 38 stories tall, will be the biggest rocket ever constructed when it's ready, hopefully in a few years (the timeline is in flux due to budgetary issues).

#### 3. NATIONAL IGNITION FACILITY

Lawrence Livermore National Security, Wikimedia Commons // CC BY-SA 3.0

Three football fields could fit inside the National Ignition Facility, which holds the largest, most energetic, and most precise laser in the world (it also has the distinction of being the world's largest optical instrument). NIF—which took about a decade to build and opened in 2009—is located at the Lawrence Livermore National Laboratory in Livermore, California. Its lasers are used to create conditions not unlike those within the cores of stars and giant planets, which helps scientists to gain understanding about these areas of the universe. The NIF is also being used to pursue the goal of nuclear fusion. If we can crack the code for this reaction that powers stars, we'll achieve unlimited clean energy for our planet.

#### 4. BERTHA THE TUNNEL BORER

When Seattle decided it needed a giant tunnel to replace an aging highway through the middle of the city, the city contracted with Hitachi Zosen Corporation to build the biggest tunnel boring machine in the world to do the job. The scope of Bertha's work had no precedent in modern-day digging, given the dense, abrasive glacial soil and bedrock it had to chew through.

In 2013, Bertha—named after Bertha Knight Landes, Seattle's first female mayor—was tasked with building a tunnel that would be big enough to carry four lanes of traffic (a two-lane, double-decker road). Bertha needed to carve through 1.7 miles of rock, and just 1000 feet in, the 57-foot, 6559-ton machine ran into a steel pipe casing that damaged it. Many predicted that Bertha was doomed, but after a massive, on-the-spot repair operation by Hitachi Zosen that took a year-and-a-half, the borer was up and running again.

In April 2017, Bertha completed its work, and engineers started the process of dismantling it; its parts will be used in future tunnel boring machines. Bertha set an example for what is possible in future urban tunnel work—but it's unlikely that tunnel boring machines will get much bigger than Bertha because of the sheer weight of the machine and the amount of soil it can move at once. Bertha's tunnel is scheduled to open in 2019.

#### 5. INTERNATIONAL SPACE STATION

NASA

The international space station is a highly efficient machine, equipped with instrumentation and life support equipment, that has kept humans alive in the inhospitable environment of low-Earth orbit since November 2, 2000. It's the biggest satellite orbiting the Earth made by humans. The major components were sent into space over a two-year period, but construction has slowly continued over the last decade, with astronauts adding the Columbus science laboratory and Japanese science module. The first module, Zarya, was just 41.2 feet by 13.5 feet; now, the ISS is 356 feet by 240 feet, which is slightly larger than a football field. The station currently has about 32,333 cubic feet of pressurized volume the crew can move about in. That's about the same area as a Boeing 747 (though much of the ISS's space is taken up by equipment). The U.S.'s solar panels are as large as eight basketball courts.

From the space station, scientists have made such important discoveries as what extended zero-G does to the human body, where cosmic rays come from, and how protein crystals can be used to treat cancer. Though NASA expects the most modern modules of the ISS to be usable well into the 2030s, by 2025 the agency may begin "transitioning" much of its ISS operations—and costs—to the private sector [PDF] with an eye on expanding the commercial potential of space.

#### 6. LIGO GRAVITATIONAL WAVE DETECTOR

The Laser Inferometer Gravitational-Wave Observatory (LIGO) is actually made up of four different facilities—two laboratories and two detectors located 2000 miles apart, in Hanford, Washington, and Livingston, Louisiana. The detectors, which took about five years to build and were inaugurated in 1999, are identical L-shaped vacuum chambers that are about 2.5 miles long and operate in unison. The mission of these machines is to detect ripples in the fabric of spacetime known as gravitational waves. Predicted in 1915 by Einstein's theory of general relativity, gravitational waves were entirely theoretical until September 2015, when LIGO detected them for the first time. Not only did this provide further confirmation of general relativity, it opened up entirely new areas of research such as gravitational wave astronomy. The reason the two detectors are so far from each other is to reduce the possibility of false positives; both facilities must detect a potential gravitational wave before it is investigated.

#### 7. ANTONOV AN-225 MRIYA PLANE

Andrew J. Muller, Wikimedia Commons // CC BY-SA 4.0

The Russians originally had a rival to the U.S. Space Shuttle program: a reusable winged spacecraft of their own called the Buran—and in the 1980s, they developed the AN-225 Mriya in order to transport it. With a wingspan the size of the Statue of Liberty, a 640-ton weight, six engines, and the ability to lift into the air nearly a half-million pounds, it's the longest and heaviest plane ever built. Mriya first flew in 1988, and since the Buran was mothballed in 1990 after just one flight (due to the breakup of the Soviet Union rather than the plane's capabilities), the AN-225 has only been used sparingly.

The monster plane has inspired new ideas. In 2017, Airspace Industry Corporation of China signed an agreement with Antonov, the AN-225's manufacturer, to built a fleet of aircraft based on the AN-225's design that would carry commercial satellites on their backs and launch them into space. Currently, virtually all satellites are launched from rockets. Meanwhile, Stratolaunch, a company overseen by Microsoft co-founder Paul Allen, is building a plane that will be wider (but not longer) than Mriya. The giant plane will carry a launch vehicle headed for low-Earth orbit.

#### BONUS: 10,000-YEAR CLOCK

This forward-thinking project, funded by Amazon and Blue Origin founder Jeff Bezos, focuses on reminding people about their long-term impact on the world. Instead of a traditional clock measuring hours, minutes, and seconds, the Clock of the Long Now measures times in years and centuries. The clock, which will be built inside a mountain on a plot of land in western Texas owned by Bezos, will tick once per year, with a century hand that advances just once every 100 years. The cuckoo on the clock will emerge just once per millennium. Construction began on the clock in early 2018. When this massive clock is completed—timeline unknown—it will be 500 feet high. What will be the impact of this one? Only the people of the 120th century will be able to answer that question.

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