TIL about the WeebSimpsons twitter account.
TIL: Today I Learned
- Thread starter Gilgamesh
- Start date
Which, as i pointed out, says nothing about the actual chance of miscarriage. At 10%, if you're over 35, it becomes 13%... which is still pretty low.
And my counter was that it's not "a LOT", as the actual numbers don't bear it out.
To quote teh wiki:
According to a computer simulation run by Henri Leridon, PhD, an epidemiologist with the French Institute of Health and Medical Research, of women trying to get pregnant, without using fertility drugs or in vitro fertilization.[24]
- At age 30
- 75% will have a conception ending in a live birth within one year
- 91% will have a conception ending in a live birth within four years.
- At age 35
- 66% will have a conception ending in a live birth within one year
- 84% will have a conception ending in a live birth within four years.
- At age 40
- 44% will have a conception ending in a live birth within one year
- 64% will have a conception ending in a live birth within four years.
Studies of actual couples trying to conceive have come up with higher results: one 2004 study of 770 European women found that 82% of 35- to 39-year-old women conceived within a year,[25] while another in 2013 of 2,820 Danish women saw 78% of 35- to 40-year-olds conceive within a year.[26]
That's so odd. I was 37 when I had my daughter. I wasn't on "high risk status". With my son, 4 years earlier, my pregnancy was high risk because there was a false positive for a neural tube defect in the triple screen test.
I wouldn't even say they conflict, people are just bad at getting statistics.
I mean, what do you think those doctors based their opinions on if not those exact types of studies?
The numbers clearly show it is harder to get pregnant as you get older, but it's not as bad as everyone seems to think.
fade
Staff member
TIL that bicycle stability is still unexplained. Commonly bike stability is explained as gyroscopic, but you can take away the gyroscopic motion and the bike is still self-stable. It's also been explained by a concept called "trail" which is "the distance the front wheel travels behind its steering axis", which is what makes caster wheels on things like shopping carts point in the direction of cart travel. But you can take this away and still have a self-stable bicycle. Here's an abstract on a proposal: http://ruina.tam.cornell.edu/research/topics/bicycle_mechanics/stablebicycle/
I assume their individual angular momenta cancel each other out, nullifying any sort of precession effect. I don't think I've ever had cause to think about it either.
--Patrick
When torque is applied to the two spinning wheels, they would want to precess in the opposite direction of each other, and thus cancel out.
So the simple concept of a gyroscope is that it resists change. The complex concept is that if you push it along its axis, then based on the direction of spin it changes* the force into another direction. Reverse the direction of spin, and the change in force based on the input force also changes exactly opposite. This results in it appearing to resist change, so the simple explanation isn't false, but it's incomplete.
By having two gyroscopes spin opposite each other on the same axis, then when you add a force to the axis one gyroscope changes that force into a force in one direction, while the other changes the force into a force the opposite direction. So they effectively cancel each other out.
This has a lot of caveats, though.
The upshot, though, is that you can perform this experiment yourself (note: I haven't done this). Take two similar items you can spin, attach them to each other on the same axis, spin them opposite each other, and see if the gyroscopic effect you expect still exists. It shouldn't. I suppose two fidget spinners on a dowel should provide the effect. Make sure they have the same rotational mass, and speed when spinning.
https://physics.stackexchange.com/q...le-gyroscope-still-have-gyroscopic-properties
Note that if this weren't true, then large jetliners would have to waste a more fuel turning, since they'd be resisting the gyroscopic effects of their turbines. Any plane with more than one engine has them turn opposite each other to avoid this issue. The forces are still there, but they cancel each other out - you just have to make sure the frame between the engines can withstand the cancellation force. The effect isn't so large that they couldn't fly if they all turned the same direction, but it's better to avoid it altogether.
Helicopters are a bit of a special case, first they really aren't that large, but second they can manipulate the pitch of the main rotor blades, forcing them up or down as needed, which takes care of the issue.
*Gross simplification, look up "precession" for more detail.
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fade
Staff member
The effect of stability is based on precession torque, which is opposing for both wheels. Here are some diagrams: http://hyperphysics.phy-astr.gsu.edu/hbase/rotv2.html
The quantity dAngle/dt is opposing for both wheels.
The quantity dAngle/dt is opposing for both wheels.
Tourbillons are meant to counteract the effects of gravity in the many positions a watch may find itself throughout the day, but I imagine it helps with the gyroscopic forces as well, though in an oscillating escapement mechanism I doubt those forces are very large at all.[DOUBLEPOST=1508774494,1508774227][/DOUBLEPOST]
When I read that I didn't believe it either. Today has been a very informative day.
I also doubt they are very large, but with an instrument such as a watch, the cumulative effect would become noticeable in short order as its accuracy drifted.
--Patrick
I think it (likely) has more to do with marketing than actual utility. Something could lose a second a year, but if your competitor advertises that they only lose a second every TEN years (or 100, 1000, etc) then it's a marketing advantage, even if for utility purposes it's useless.
Note: this is discussing a WRISTWATCH. Such inaccuracies make BIG differences in other clock-based applications, like GPS.
Or TLS. Seriously, it's almost at least once/day I have to deal with someone's "The Internet isn't working." "Did your battery die yesterday?" "Yes." "Fix your date/time, it'll be fine."
--Patrick
Oh yes. Tourbillons are marketed to people who have money and are interested in unique mechanical timepieces. The reality is that a crystal digital watch you can get from walmart for $9.95 is more accurate and lasts ten years on the built in battery.
It's a hobby, and scratches an itch for certain people, and it's fascinating for those of a mechanical bent of mind.
I've been wanting a copy of George Daniels "Watchmaking" for years now, despite knowing I'm never going to build, repair, or probably even own a mechanical watch. The precision manufacturing, etc fascinate me. Which is why I subscribe to youtube channels like Clickspring.
I guess I'm getting off topic.
For those that care about this stuff, the minuscule difference is enough for them to choose one product over another, but its effects are very, very small.
I'm guessing part of the handshake rejects you if your delta is off by too much? But even then, it won't reject over a 1-second delta (at least no standard TLS I've ever heard of) given that round-trip times over 1000ms (1s) are easily demonstrable.
TLS itself doesn't inherently require clock synchronization, but many of the protocols built on it do, primarily to avoid replay attacks:
https://serverfault.com/questions/8...ronicity-can-secure-protocols-tolerate/852423
Looks like +/- 5 minutes is common.
Agreed, but it was the sub-second accuracy per 1000s of years that Patrick was claiming was important that I had issue with. As I said originally, very few things need that, and not in a wristwatch. Hell, if you lost a second every year, it would still take around 300 years for such a watch to not be suitable for TLS!
You are conflating my statements. Nobody seriously expects things like GPS or TLS to rely on/interact with any sort of mechanical timepiece. My first statement was merely an assertion that, with an uncompensated mechanical wristwatch, not only would the time vary, but the discrepancy itself would vary based on the amount of movement the watch endured, leading to frustration as the person wearing it tried to compensate for a watch that did not gain/lose a consistent amount of time every day.
My second statement was merely a sort of "...and my axe!" regarding having to deal with technological dependency on accurate timekeeping.
Losing one's battery often resets a clock back to 2000 or something. The Internet then complains. Most frustrating are the ones where someone sets the correct date and time...but then doesn't fix the year for some reason.
--Patrick
That's okay, you just need another head to spin in the other direction and cancel each other out.
I thought guys already had two heads. Y'all need another?
I feel so naked without a watch. I own five, and I'm thinking about splurging and buying a custom-built one from a watchmaker in Toronto.
If you count my fitbit, I have the band tan-line to prove I wear it every day.
fade
Staff member
I'm imagining you wearing all 5 80s style.
Hi Chad!
TIL who does the song on the ABC college football commercials. And I wish I hadn't.
Every day. I feel naked without one.
I haven't worn a watch in five years, and I still feel naked without one.
I don't get it...?