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YouTube // engineerguy

How Retractable Ballpoint Pens Work

YouTube // engineerguy
YouTube // engineerguy

We've all used clicky ballpoint pens. I'll admit, I fiddle with one on a daily basis, clicking it over and over—those clicks are very satisfying. But what are the details of the mechanism that allows the tip to be extended or retracted? Although I've taken apart many of my pens (another nervous habit that I enjoy, especially during long meetings), I never spent much time thinking about the engineering involved.

It turns out that there are various different ways to build a retractable pen. But in this four-minute video, we see how the hugely popular Parker Jotter ink pen works, using a series of surprisingly clever cams and a spring. Let Bill Hammack, The Engineer Guy, explain:

Note: If you'd like to read the original patent, Google has it (complete with plenty of minor scanning errors in the text). The illustrations are beautiful.

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architecture
Engineers Have Figured Out How the Leaning Tower of Pisa Withstands Earthquakes
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iStock

Builders had barely finished the second floor of the Tower of Pisa when the structure started to tilt. Despite foundational issues, the project was completed, and eight centuries and at least four major earthquakes later, the precarious landmark remains standing. Now, a team of engineers from the University of Bristol and other institutions claims to have finally solved the mystery behind its endurance.

Pisa is located between the Arno and Serchio rivers, and the city's iconic tower was built on soft ground consisting largely of clay, shells, and fine sand. The unstable foundation meant the tower had been sinking little by little until 2008, when construction workers removed 70 metric tons of soil to stabilize the site. Today it leans at a 4-degree angle—about 13 feet past perfectly vertical.

Now researchers say that the dirt responsible for the tower's lean also played a vital role in its survival. Their study, which will be presented at this year's European Conference on Earthquake Engineering in Greece, shows that the combination of the tall, stiff tower with the soft soil produced an effect known as dynamic soil-structure interaction, or DSSI. During an earthquake, the tower doesn't move and shake with the earth the same way it would with a firmer, more stable foundation. According to the engineers, the Leaning Tower of Pisa is the world's best example of the effects of DSSI.

"Ironically, the very same soil that caused the leaning instability and brought the tower to the verge of collapse can be credited for helping it survive these seismic events," study co-author George Mylonakis said in a statement.

The tower's earthquake-proof foundation was an accident, but engineers are interested in intentionally incorporating the principles of DSSI into their structures—as long as they can keep them upright at the same time.

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U2’s 360-Degree Tour Stage Will Become a Utah Aquarium Attraction
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LLPA

The immense stage that accompanied U2 on the band’s 360° Tour from 2009 to 2011 is getting an unexpected second life as a Utah educational attraction. It will soon be installed over a new plaza at the Loveland Living Planet Aquarium outside Salt Lake City.

The Claw, a 165-foot-tall structure shaped like a large spaceship balanced on four legs—a design inspired by the space-age Theme Building at Los Angeles International Airport—was built to house a massive speaker system and cylindrical video screen for the band’s performances. Underneath it, a 360° stage allowed U2 to play to audiences surrounding the structure in all directions. To make it easier to tour 30 different countries with the elaborate system, which took more than a week to put together at each concert location, the band had several versions built.

U2 and its management have been looking for a buyer for the 190-ton structures since the tour ended in 2011, and it seems they have finally found a home for one of them. One of the two remaining Claw structures is coming to the Utah aquarium, where it’s being installed as part of a plaza at the institution’s new, 9-acre Science Learning Campus.

A four-legged, industrial-looking video-and-sound-projection rig rises over a crowd at a concert
The Claw at a Dublin concert in 2009
Kristian Strøbech, Flickr // CC BY 2.0

As the only Claw in the U.S., the alien-looking feat of engineering will be "preserved and sustainably repurposed as a Utah landmark and symbol of science exploration and learning," according to the aquarium's press release. As part of the expansion project, the 2300-square-foot stage system will play host to festivals, movies, and other special events in two venues, one with 7000 seats and the other with 350.

The $25 million Science Learning Campus hasn’t been built yet—construction is starting this fall—so you’ll have to wait awhile to relive your U2 concert experience at the aquarium.

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