...an ordinary lawnmower sucks air up into the mower body causing the grass to stand vertically, which allows the blade to slice evenly at the bottom of the grass.
To demonstrate this in another way, a vacuum hair clipper does the same thing. It sucks hair into it before it is cut so that a really precise cut can be made. The lifting of the grass is actually caused by the tab on the back of the mower blade which causes air lift and raises the grass up.
By filming a lawn mower in action with a super fast camera, that in turn gives wonderful slow motion, you can see the blades of grass being lifted up just before being cut.
ICYMI, Friday's links are here, and include medieval fitness programs, an interactive map showing all of the roads leading to Rome, lost survival tips from 100 years ago (with illustrations), and the Great Sperm Race, scaled up to human size (plus bonus Monty Python).
In this video from WIRED, John Collins (website), aka "The Paper Airplane Guy," who's devoted the last two decades of his life to paper airplanes, talks about how he designs and flies the world's best and coolest paper planes.
ICYMI, Friday's links are here, and include the science of knuckle cracking, how a simple artificial heart could permanently replace a failing human one, the legend of Blackbeard’s silver-plated skull, and a look inside the FBI's pre-computer fingerprint factory.
This is surprisingly fascinating. Living near sea-level or on flood plains have forever been risky propositions, calculated (or uncalculated) risks. All the same, people do it.
Yesterday was President James Garfield's birthday - when he was shot, Alexander Graham Bell showed up with a metal detector to try to locate the bullet.
ICYMI, Friday's links are here, and include the anniversaries of the Gettysburg Address and the opening of the Suez Canal, 3 foot long crabs that hunt birds, the pigeon’s rump cure for childhood seizures, and what it's like to be an Amazon.com "fake" reviewer.
Using a series of wooden poles and beams, this kid shows his dad how to build Leonardo da Vinci's (wiki) self-supporting arch bridge, also known as the emergency bridge, without nails, screws, rope, glues, notches, or any other fasteners.
They've made this with 5 sections, but you could make it with many more - each section increases the height as well as the length. I'm sure there's an upper limit to the number of sections that would work, but I don't know what it is.
In 1482, before he was famous, Da Vinci (April 15, 1452 - May 2, 1519) was looking for work. He sent his resume to the Duke of Milan, listing several useful skills he could provide, including the bridge:
I have a sort of extremely light and strong bridges, adapted to be most easily carried, and with them you may pursue, and at any time flee from the enemy; and others, secure and indestructible by fire and battle, easy and convenient to lift and place. Also methods of burning and destroying those of the enemy.
