Today I Learned

[fresh_42]

When I took driver's ed (so many years ago), it was commonly said that you need 1 car length per 10 miles/hour of velocity to safely stop.

I would not really on that measure on high speeds. Ten car lengths at 100? Never, ever!

 

[BillTre]

I was also told that (in the US), the dashes in the middle of the road (where passing is permitted) had a wavelength of about a car length.
Count the dashes.

 

[fresh_42]

I was also told that (in the US), the dashes in the middle of the road (where passing is permitted) had a wavelength of about a car length.
Count the dashes.

I remember well the following situation. I was behind another car and we both have driven about 100 on the left lane. Then a bus driver decided to overtake a truck, both around 55. Then the bus driver looked into his rear view mirror and got back to the right as we were approaching fast. Unfortunately, there was another truck in front of the bus who saw the bus attempting to overtake, so he as well changed to the left lane to overtake a third slow vehicle ahead of both: truck and bus. However, the truck driver didn't check twice and relied on the bus driver's decision, so he stayed on the left. As a result, we both had to decelerate from 100 to 50 something, and I can tell you, this took essentially more than 10 car lengths $\sim$ 30-40 meters. This measure you've been told is a secure method to have an accident if above 50.

 

[Buzz Bloom]

When I took driver's ed (so many years ago), it was commonly said that you need 1 car length per 10 miles/hour of velocity to safely stop.

I would not really on that measure on high speeds. Ten car lengths at 100? Never, ever!

The rule of thumb I have learned is to keep about three seconds behind the car in front of me. The faster you go,, the larger this distance is. I find this easier to determine than trying to count car lengths. You spot something along the road which the car in front passes, and then count the seconds until you pass the same object.

 

[fresh_42]

Duplication deleted

You accidentally (?) deleted both versions. Shall I restore this one?

 

[Buzz Bloom]

No. My intention was post # 2489.

Regards,
Buzz

 

[fresh_42]

The rule of thumb I have learned is to keep about three seconds behind the car in front of me.

That would had given me 130 meters. Probably around the distance which I actually needed. Our rule of thumb is half the speedometer (in km/h). That would have given me 80 meters, which I think hadn't been enough. Anyway, the main experience was, that kinetic energy counts, and this is quadratic in speed, so what works for low speeds doesn't necessarily work at higher speeds. And all three rules so far are linear in speed!

 

[BillTre]

Anyway, the main experience was, that kinetic energy counts, and this is quadratic in speed, so what works for low speeds doesn't necessarily work at higher speeds. And all three rules so far are linear in speed!

Disappointing.
I thought you were going relativistic.

 

[jim hardy]

there's a real delay between receiving signals, processing them, and then acting on them that your brain has to take into account or else you smash into a pole or person coming around a corner or something.

I wonder what part of the brain does that. I marvel watching a hawk or hummingbird navigate through tree limbs. I can't even think that fast.

 

[nitsuj]

Such a subtle thing that when and where it counts, shows a vast difference in abilities; between me and some pro athlete lol

The more you practice the more an action becomes a reflex not requiring nearly as much processing time An athlete also need a good sense of anticipation of his opponent's next move. It is easier to fake out an amateur.

Anyone can train like a "pro athlete".

Almost implicitly some variations of our genetics are better at such brain/nervous system tasks than others...Ask Michael Jordan lol

 

[fresh_42]

What a surprise!

https://digest.bps.org.uk/2017/04/0...ted-people-are-less-into-conspiracy-theories/

 

[mfb]

What a surprise!

https://digest.bps.org.uk/2017/04/0...ted-people-are-less-into-conspiracy-theories/

Clearly the result of the brainwashing in education! Here, I have this website of someone who disappeared under mysterious conditions shortly after revealing this!

 

[collinsmark]

I've always wondered how much of your brain's 'processing power' goes into predicting the near future. Not in a tarot card, palm reading, or other magical sense, but in the sense that there's a real delay between receiving signals, processing them, and then acting on them that your brain has to take into account or else you smash into a pole or person coming around a corner or something.

On a somewhat related note (sort of related, or at least sort of in-part), this new Physics Girl episode just came out today:

 

[TheDemx27]

I've always wondered how much of your brain's 'processing power' goes into predicting the near future. Not in a tarot card, palm reading, or other magical sense, but in the sense that there's a real delay between receiving signals, processing them, and then acting on them that your brain has to take into account or else you smash into a pole or person coming around a corner or something.

Speaking of sight, I've always been interested in eye movement. You never ever see the wooshing eye movement when you move your eyes from one area to another. Your brain just stops formulating and constructing the world for a few milliseconds and just cuts off perception until your eyes have stopped moving. What does your evolution programming do to create continuity in experience? It slows down your perception of time passing to aid in you thinking that your visual feed was never cut off at all, because no time has passed since you were last seeing input.

https://en.wikipedia.org/wiki/Time_perception#Eye_movements_and_"Chronostasis"

 

[Drakkith]

Speaking of sight, I've always been interested in eye movement. You never ever see the wooshing eye movement when you move your eyes from one area to another. Your brain just stops formulating and constructing the world for a few milliseconds and just cuts off perception until your eyes have stopped moving.

You sure about that? I swear I can see a small amount of blur or 'whoosh' when quickly looking back and forth.

 

[pinball1970]

I came across this stat when looking up something (physics for psychics on another thread)

https://www.telegraph.co.uk/educati...929672/Why-dont-more-girls-study-physics.html

Everyone knows about Einstein are the women trail blazers not promoted enough to kids?

Marie Curie, Jocelyn Bell, Rosalind Franklin, Emmy Noether?

 

[kyphysics]

Currently reading Peter Lynch's, One Up on Wall St., and learned that the bear market of the early 1970's took 15 years for the Dow and other averages to regain the prices reached in the mid-60's.

Dang...15 years!

Talk about needing patience to hold onto stocks!

 

[jim hardy]

You never ever see the wooshing eye movement when you move your eyes from one area to another. Your brain just stops formulating and constructing the world for a few milliseconds and just cuts off perception until your eyes have stopped moving.

When driving at night i am bothered by modern luxury automobile taillights that are pwm LED's . When i move my eyes i see a series of dots and it's really disturbing.

Check it yourself next time you're behind a Cadillac or Lexus .

i'd say perception doesn't stop it's just dulled.

old jim

 

[gleem]

I think the retina also has what is called persistence. i.e, the response to light does not decrease instantaneously to zero when the stimulus is remove. so a moving bright light will appear as a streak in your vision. The brain has to process the changing signal as well as it can and sometimes it doesn't get it right. Witnesses to accidents often do not agree with one another.

 

[nitsuj]

When driving at night i am bothered by modern luxury automobile taillights that are pwm LED's . When i move my eyes i see a series of dots and it's really disturbing.

Check it yourself next time you're behind a Cadillac or Lexus .

i'd say perception doesn't stop it's just dulled.

old jim

I agree,

I was watching a stream of stones being flung from a conveyor and was "playing" with following the stones visually. It was fun to see the stream of stones go from a blur, to seeing individual stones if I followed them visually.

 

[fresh_42]

TIL that the rate of applications for naturalization increased by 1200% since Brexit. (Has been named as a cause for the increasing number of double citizenships.)

 

[mfb]

In which country from which country?

 

[fresh_42]

In which country from which country?

From UK to Germany. As they keep their passport, a second one simply enlarges their options. Would be interesting to know how the British tax laws are, because Americans wouldn't have this option if they don't want to get taxed twice, as the US taxes by citizenship and not by location.

 

[CWatters]

British and European taxes are generally similar with different rates and allowances/deductibles. Some tax on where you are 'ordinarily resident' which isn't always the same as where you are living. This can sometimes mean you are you are taxed twice but we have double taxation treaties. Not all EU countries have Capital Gains tax so it may pay to realize gains before/after emigrating. Should always take tax advice before emigrating or it can cost you big time.

 

[Drakkith]

Today I learned that, fully fueled and loaded, the Saturn V launch vehicle + Apollo spacecraft had a mass of nearly 3 MILLION kg! Each of the five F-1 engines on the 1st stage burned just over 2500 kg of fuel and oxidizer each second, pushing a combined total of 12,890 kg of mass out the back and propelling the vehicle with 35 MN of force! (that's MN for mega-Newtons. Yes, MEGA Newtons! Not your ordinary Isaac Newtons, but Isaac with his superhero pants on!) For those here in the states, that's 7.891 million pounds of thrust.

It sure beats the fins off of my 20 oz model rocket I had as a kid!

 

[mfb]

pushing a combined total of 12,890 kg of mass out the back and propelling the vehicle with 35 MN of force!

48 GW of power, about 10 GW per engine.

Each F-1 had a fuel pump with a power of 40 MW.

 

[jim hardy]

No chlorine in RP1.
Shuttle boosters had solid fuel, aluminum with polyvinyl chloride binder and ammonium perchlorate oxidizers -

and they complain about chlorine from car air conditioners ?

 

[Drakkith]

48 GW of power, about 10 GW per engine.

Each F-1 had a fuel pump with a power of 40 MW.

Speaking of power, I just launched my first Saturn V in Kerbal Space Program (with a realism mod added) and my S-IVB stage had exactly zero power. Because I forgot to add fuel to the fuel tank. (I blame the ground crew. The sign said "Full Service". At least it will once I get back!) Luckily it was an Apollo 8 style mission with no LM and I still had enough delta-v to get to the Moon and back.

Interestingly my orbital velocity around the Earth was only around 200 m/s after my TEI (trans-earth injection, the engine burn to get out of the Moon's orbit and back to Earth's), while my orbital velocity around the Moon was somewhere between 1k and 2k m/s. Nothing like trying to understand linear velocities along curved paths while transitioning between moving reference frames in three dimensions to get the brain juices flowing!

 

[Fewmet]

Today I learned how to identify the back locust tree. This came shortly after I learned that the black locust has thorns.

 

[phinds]

Today I learned how to identify the back locust tree. This came shortly after I learned that the black locust has thorns.

And did you learn that the hard way ?

 

[BillTre]

Today I realized that a guy, Shaun, who I deal with occasionally and who recovers tissues from deceased donors for transplanting, is...

Shaun of the Dead!

 

[Phys12]

Today...a few days ago, actually...I learned that the capital of Turkey is *not* Istanbul. I had been living a lie for the past 19-20 years.

 

[jim hardy]

Today I learned how to identify the back locust tree. This came shortly after I learned that the black locust has thorns.

Yep they'll go clear through a boot or tractor tire.

 

[jtbell]

Just now I learned that the melody for "God Save the King/Queen", which is used on this side of the pond for "My Country 'Tis of Thee", was used at George Washington's inauguration in 1789, 33 years before the latter song was written. On that occasion the words were:

Hail, thou auspicious day!
For let America
Thy praise resound.
Joy to our native land!
Let every heart expand,
For Washington's at hand,
With glory crowned.

I wonder if the choice of melody was politically deliberate.

Was God Save the Queen played at John McCain's funeral? (BBC News)

 

[fresh_42]

Wiki says the melody for God save the Queen has been first published in 1744 with similar even older melodies. So the winner are the British in this case. Surprisingly "The Jacobites also adopted the song with the introductory words "God save great James our king" ". Seems it served each side even before Washington.