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Sunday, July 15, 2018

The Physics of How Lawn Mower Blades Cut Grass (at 50K frames per second)

Interesting Engineering on Smarter Every Day's super slow motion video (below) of a lawnmower:
...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.

Friday, July 13, 2018

Friday links

Apocalypse alert: supermoon, solar eclipse and Friday the 13th. Paraskavedekatriaphobia: Why is Friday the 13th Considered Unlucky?

July 14 is Bastille Day. Here's Jonah Goldberg's classic article on the subject: The French are Revolting.

A Brief History of Trial by Combat.

Supercut: 100 Greatest One-Liners Before The Kill.

Mozart’s Much Less Family Friendly Works (Some NSFW language - apparently his sense of humor had a scatological component).


ICYMI, Thursday's links are here, and include the 19th century fight over Sunday mail delivery, the art and science of creating ice in the desert 2,000 years ago, sporting pastimes from the Georgian era, and some male contraceptive advice (just wear a polyester sling, and let the heat and electrostatics do all the work), with bonus Monty Python.

Thursday, July 12, 2018

Thursday links

The massive 19th century fight over Sunday mail delivery.

The U.S. Air Force Learned to Code and Saved the Pentagon Millions.

Male contraceptive advice: just wear a polyester sling, and let the heat and the electrostatics do all the work, with bonus Monty Python.

Skittles and Nine Holes, or Bumble Puppy: sporting pastimes in the Georgian era.

The Cutting-Edge Science That Can Turn Everyday Objects, Like a Bag of Chips, Into a Listening Device.

How People Created Ice in the Desert 2,000 Years Ago: the ancient art of "night-sky cooling."

ICYMI, Monday's links are here, and include Nikola Tesla's birthday, the U. S. Navy's 1920's ice cream barge, how alcohol and caffeine helped create civilization, and eye-searing fashion ads from the 1970's.

Tuesday, July 10, 2018

Male contraceptive advice: just wear a polyester sling, and let the heat and the electrostatics do all the work

Hey, it's science! 

So, is birth control just a women’s issue? Men are equally involved in producing a baby, and there are a few male-centric birth control options (i.e., condoms) available. But there’s definitely room for new male contraceptives–especially ones that aren’t permanent and don’t require last-minute application. And that’s where the polyester comes in. 

No, not this kind of sling, dummy.
Apparently, simply wearing a polyester sling (I suppose you could get one that isn't polyester, and line it yourself) around the scrotum can produce sperm-free semen (azoospermia), presumably from the heat (what’s sweatier than polyester?) and the electrostatics. The sling must be worn for months before it’s effective, and it takes another couple of months, after removal, to reverse the effects.

This makes sense, if you give it any thought (which I never have) because your balls hang low for more than one reason, and one of those reasons is temperature regulation. In order for sperm to mature successfully, they need to be kept a few degrees lower than normal body temperature, so keeping them below the body is a good way to keep things cool. 

Related stuff: 

Swinging high and low: Why do the testes hang at different levels? A theory on surface area and thermoregulation. 

and this:

Scrotal Asymmetry In Man And Ancient Sculpture which discusses the fact (?) that the left side generally seems to hang lower. 

Previous studies in dogs wearing polyester underpants showed that the dogs had reduced sperm count under those conditions:
"A recent study has shown that dogs, while wearing polyester underpants, had a diminished sperm count which was reversible when the pants were removed. In contrast, dogs wearing cotton pants showed insignificant semen changes.”
Here's the abstract from the paper on humans mentioned back at the beginning of this post (I don't, unfortunately, have a link to the dog paper), which, by the way, also fits into the "tax dollars at work" category, since it's from the NIH:


"Every 2 weeks, a physician at the Faculty of Medicine at Cairo University in Egypt examined 14 32-47 year old male volunteers wearing a polyester scrotal sling day and night for 12 months to determine if polyester fabrics can act as a contraceptive in men. 

They changed the sling only when it became dirty. None of the men dropped out of the study. The sling did not cause any complications or reactions. Their partners took an oral contraceptive until 3 sperm samples proved the men to be azoospermic. The men became azoospermic from 120-160 days (mean 139.6 days) after 1st putting on the sling. They remained azoospermic throughout the study. None of the partners became pregnant during the study. All 5 couples who wanted a pregnancy after the study period did indeed conceive. 4 had normal live births and 1 a miscarriage. The volume of their testicles fell greatly from 22.2-18.6 sd ml during the 12 months (p.05), but returned to pretest levels 75-135 days after removal. Further the mean rectal-testicular temperature difference was lower 3 months after wearing the sling than it was before they wore it (1.3-3 degrees Celsius; p.001). 3 months after they stopped wearing the sling, the mean rectal-testicular temperature difference reverted to normal. 

The polyester in the sling generated greater electrostatic potentials during the day than at night (326-395 volt/sq. cm. vs. 142-188 volt/sq. cm.; p.01). This was a result of the friction between the scrotum and the polyester sling. Germ cells of the seminiferous tubules still exhibited degenerative changes 6 months after removal of the sling. Within 140-170 days after removal, sperm concentration levels returned to pretest levels (40 million/ml). Apparently the electrostatic field effect and the disordered thermoregulatory effect of the polyester sling produced azoospermia. In conclusion, the sling is a safe, acceptable, inexpensive, and reversible method of contraception in men.”

Borat's mankini might work

 for this purpose
Somewhere in reading about this stuff I ran across this (read the whole thing), on the dangers of blogging (if you're male, that is):
When bloggers write, with laptops, seated,
Bits of them get overheated—
Sitting in their rooms, retreated
To their hidden cloisters.
If I should hear “Well done! Well done!”
I hope they mean my writing’s fun
And not some cruel and heartless pun
About my mountain oysters.
That reminded me of the Family Guy episode "Hell Comes to Quahog" (I couldn't find it on youtube), which is the episode in which Superstore comes to town. It's just after Peter gets a job at Superstore :
Peter: Boy Meg, I am so looking forward to this job. 
Brian: Peter, I can't believe you're working for Superstore USA. How could you sell out like that? 
Peter: Because Brian, they have industrial sized air conditioning. And I'm tired of sitting in ball soup.
And, of course, it's impossible to touch on this subject without including Monty Python's classic Every Sperm is Sacred skit from The Meaning Of Life:

Monday, July 9, 2018

Monday links

July 9th is Nikola Tesla's birthday: bio, Tesla coil music, Tesla vs Edison rap battle, history, videos and links.

How Alcohol and Caffeine Helped Create Civilization.

Making the World’s Largest Lemon Battery for a Lemon-Powered Car.

Fashion Ads From The 1970s. Be warned - you can't unsee these.

Science: U.S. women have a significantly larger mean breast volume than women born in other countries.

Why the U.S. Navy Once Had a Concrete Ice Cream Barge

ICYMI, most recent links are here, and are all Independence Day-related: Lincoln's 1858 speech on the eternal meaning of Independence Day plus speeches from Coolidge (1926) and Reagan (1986), the text of the Declaration of Independence, founding fathers stories, how the breaking news spread in 1776, the science of fireworks and of barbecue, and Independence Days from science fiction.