How Are Speed Limits Enforced By Aircraft?

I'll answer the titular question last, and start off with a few different interesting road signs and road-related trivia I've run across in my time.

You Can Hack Into Road Signs

I feel obliged to say you definitely shouldn't do this, but if you were curious how to do it,

here's a link.

There are some great examples on that page but here's one representative image:

Photo Credit: Paul Anderson

A Few Random Interesting Signs

This is a sign for "Thin Ice"

Photo Credit: WordShore

Photo Credit: Tim Ellis

Photo Credit: Richard Masoner

Photo Credit: Joe Dunckley

Photo Credit Gabe Kinsman

How Often Do Speed Limit Signs Need to be Posted?

I did a little digging, and so can you, about how often speed limit signs are required to be posted. As it turns out, by federal law, signs only need to be posted at two places: entrances to the state, and at "jurisdictional boundaries to metropolitan areas." Everything else is a recommendation, including entrances to a freeway and where the speed limit changes. That struck me as interesting. These recommendations are nearly always followed, but they aren't strictly speaking, required.

In reality, every state has adopted something called the Manual on Uniform Traffic Control Devices, or MUTCD. This manual has stricter specifications about speed limit signs, along with every other sign you see on the road. The MUTCD is the main reason you can drive from Maine to California and never be confused along the way, because road signage is very standardized. To avoid going down a rabbit hole from which I'll never escape, I'm going to set down the MUTCD and move on.

I lied, one more thing:

"Speed" is defined in a few interesting ways in this manual. One of the most used is the "85th percentile," the speed under which 85% of vehicles travel. Now I'm done.

Maximum Speed Limit Limits Around the World

Here's a link to the original

Interstate Numbers Have Meaning.

If an interstate highway's number is even, it travels east / west, if it is odd, it goes north / south. Think about the highways near you, it holds true across the US.

Some highways (C-470 near where I live) travel in large loops. These are named for the direction they mostly travel

What's the Deal With Hawaii?

Hawaii has interstate highways. Interstate. What gives? It turns out the name simply means the highways receives federal funding, which is true in Hawaii. Good thing too, because the H-3 in Hawaii is not only one of the most beautiful segments of the US Interstate system, but also one of the most expensive. Feast your eyes:

Photo Credit: Marvin Chandra

The H3 on the Hawaiian island of Oahu cost about 80 million per mile to construct, with a total cost of around 1.3 billion. Here's a newspaper article on the building of the H3.

Don't Block the Box

Photo Credit: Richard Winchell

These signs can be seen in New York City and other large cities around the world. Their aim is to avoid gridlock by issuing fines to cars that block the intersection itself, of the "box"

Stolen Road Signs

Here is a short list of oft-stolen street signs around the world. See if you can detect a theme:

• Richard Bong State Recreation Area;  Brighton, Wisconsin
• Stoner Avenue; Bemidji, Minnesota
• High Street; Denver, Colorado
• Mile Marker "420;" I-25, Colorado*
• Katie's Crotch Road; Portland, Maine
• Butt Hole Road; Conisbrough, South Yorkshire, England
• Bat Cave; North Carolina
• Fucking; Austria (named for Adalpertus Fucingin)
• Shitterton; Dorset, England

Note* the "420" mile marker in Colorado is no longer stolen (though I doubt they moved the sign the required 53 feet south to compensate):

Photo Credit: Bill Keaggy

Road Crossings in the UK

Here's a random link for typeface geeks

If you've ever driven in the UK, watched the show "Sherlock," or saw a friend post a picture from the Abbey Road street crossing...

Photo Credit: Mage Who on YouTube

...you may have wondered what the deal is with those zigzag lines. It turns out they are there to signal cars not to change lanes or park near the pedestrian crossings so pedestrians can see the oncoming traffic.

Pictured above is a "zebra crossing," but not all crossings in the UK are this same type. There are also Pelican, Puffin, Toucan, and Pegasus Crossings

Zebra Crossings often come with "Belisha Beacons," (right) named for Leslie Hore-Belisha, the Minister of Transportation in 1934, who put up these beacons around the UK.

In addition to familiar Zebra Crossings, the UK has Pelican (Pedestrian Light Controlled) crossings that have auditory and tactile feedback for the visually impaired, and a light to stop traffic.

A Pedestrian User-Friendly Intelligent (Puffin) crossing uses sensors to detect pedestrians and control traffic flow based off their presence.

A toucan crossing is passable by bicycles as well as pedestrians, so two can cross it. Get it? Two-can, Toucan? Great name.

Finally, a Pegasus crossing is for horses. There's no clever pun there, just that the last few types of crossings got bird names, so the horse crossing became known by the name of a flying horse, Pegasus.

How are Speed Limits Enforced By Aircraft?

Photo Credit: Paul Bevan

Finally! I always thought it would be worth the cost of the ticket to get pulled over by a fighter jet, but that's not quite how the process works.

First, there is a designated area of a known distance that a small fixed-wing aircraft will patrol. The aircraft carries a pilot and a spotter. The spotter will time cars along this distance using some specialized timing equipment, and can figure out exactly how fast a car has traveled through the area. The spotter then informs a patrol car on the ground to issue a ticket, not needing a reading from a radar gun.

The cost for operating a small aircraft hovers around $150 an hour. In order to make this program profitable, the aircraft team needs to issue several tickets in that hour. Considering that the aircraft team as well as the serving officer need to appear in court, and the aircraft team often requires overtime pay, these programs are not very profitable. Many programs are justified by looking for other crimes such as illegal plant growth (mostly pot, but occasionally an particularly endangered ficus) and illegal hunting activity.

One way to cut down on costs may be to employ ticket-issuing drones, which are coming home to roost with fewer overseas engagements.Luckily, this is still in a legal grey area, for now.

On that happy note,

Cheers, 

    - Scott Sieke

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Do Australian Toilets Flush Differently?

The Coriolis effect is responsible for all kinds of interesting phenomena. It makes hurricanes spin differently in the northern and southern hemispheres, it makes toilets go counterclockwise in the northern hemisphere and clockwise in the southern, and makes it really difficult to play catch on a spinning merry-go-round. Or does it?

At the time of writing, Wikipedia says this about the Coriolis force:

"In physics, the Coriolis force is an inertial force (also called a fictitious force) that acts on objects that are in motion relative to a rotating reference frame. In a reference frame with clockwise rotation, the force acts to the left of the motion of the object. In one with anticlockwise rotation, the force acts to the right."

That didn't help me much because I lost steam partway through due to jargon. I think of the Coriolis effect as "things acting weird because the world is rotating underneath them." For example, if two friends are sitting on opposite sides of a spinning merry-go-round playing catch, the ball veers unpredictably.

This happens because once you release the ball it no longer cares about what the merry-go-round is doing beneath it, it just travels along the path it was thrown. If you're on the merry go round in a different frame of reference that straight line looks curved. The "force" moving the ball is what is responsible for the Coriolis effect.

In this case, you are the red dot, and the
black ball is the object being thrown

So far so good, right? The curving of the ball is a bit odd, but here's where it gets really interesting. In our example, the Coriolis effect was quite dramatic because the merry go round was moving quickly relatively to the motion of the ball; the merry-go-round moved about 25% of the way through its rotation while the ball was in the air. Let's consider a larger rotating frame of reference: our planet.

The earth rotates once per day (I think). The a equator has a much larger circumference (40,076 km) than do the poles (0 km). Over the course of one day, the poles just spin in place around the earth's axis, while a point on the the equator needs to travel the full 40,076 km in that same time. This means that the speed the Earth travels at differs at different latitudes.

*assuming a spherical Earth, not a oblate spheroid (I can't do the math for the
real shape, but these should be really close to the actual numbers)

If you throw a ball on the earth, the earth will rotate beneath the ball as it is in the air. The Coriolis effect doesn't doesn't show up very often, because many things aren't in the air long enough to matter; it does however show up in a few interesting places: long distance shooting and field goal kicks in (American) football.

In the field, snipers work in teams of two, a marksperson and a spotter. The spotter has a very interesting job: they must consider a whole spectrum of effects to preserve accuracy. A spotter must accurately find the range to ensure the parabolic trajectory hits the target at the right point (including shooting uphill or downhill where gravity acts at an angle, making the math much harder). Other factors the spotter must take into account include the wind conditions both at their location and downrange, updrafts caused by radiant heat, the curvature of the earth, a potentially moving target, humidity, and you guessed it, the Coriolis effect. If you are shooting directly North, the bullet will deflect to the right by a matter of a few inches. If you are shooting directly South, the bullet will deflect to the left. An East or West facing shot will have a smaller effect, but will travel either farther or less far respectively.

The red lines in the middle are the cardinal directions,
and the blue lines above are the apparent trajectories
of bullets fired in those directions.

In football field field goal kicks, the Coriolis effect may make a small difference, a matter of centimeters, if the ball is kicked either North(ish) or South(ish). This is such a small effect that it has probably never made a difference in an actual game, but it may have in cases where a few centimeters might be the difference between bouncing off the uprights and going through the goalposts:

On to hurricanes and toilet bowls. Hurricanes do rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern. The structure of a hurricane looks roughly like this:

Winds are trying to rush into the
low pressure zone in the middle

The Coriolis force, shown in yellow, displaces these arrows to the right in the Northern Hemisphere. This means the winds move to the right, and the effect is that the whole thing begins to spiral:

This is why hurricanes spin counterclockwise north of the equator and Clockwise south of the equator.

On to the topic at hand (finally): toilets. As we have seen, the Coriolis force shows up in large-scale systems, where objects are either in the air for a long time, travel very long distances, or are massive in scale. A toilet bowl fits none of these criteria. The fact is that the Coriolis force is vanishingly small and insignificant on the scale of one or two feet. The direction a toilet bowl flushes is dominated by the shape of the bowl and the direction of the water jets that are released from the top of the bowl.

Phil Plait, in his book Bad Astronomy talks about a small Kenyan village right on the equator. For a few bucks you can pay someone to give you a "demonstration of the Coriolis
effect." There are two basins, each in different hemispheres, one that drains clockwise, the other drains counterclockwise. This is because the one to the North has right-facing jets, and the the one in the South has left facing jets. Simple as that.

The interesting thing is that you actually can see the Coriolis effect in a draining water basin, but you have to control variables very carefully or random effects will trump the Coriolis effect. Enjoy:

Note* It's cool to sync the videos, but not necessary. If you don't want to, just watch the "North" video. If you want to sync them up, grab your phone and your computer, or two computers, or two tabs. Here are the individual links:

North

South

Destin and Derek have fantastic channels and you should check them out, their passion for science is infectious. 

Cheers,

   - Scott





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What Are Gravitational Waves?

About a month ago, two specialized observatories called LIGO announced the first direct detection of what are called gravitational waves. This discovery represents another step in knowing that science is on the right track with this whole "relativity" thing Einstein figured out a century ago. I'll answer the two most common questions I've gotten from my friends when they've been kind enough to let me talk about gravitational waves for entirely too long.

"What are gravitational waves?"

Here is a great primer from Brian Greene:

Gravitational waves can be thought of like waves in the surface of a lake. When there is some disturbance in the lake, say a poodle jumps into the water, waves propagate across the surface. The same goes for gravitational waves, but rather than propagating through water, they propagate through space and time.

A bug on the surface of the water a little ways away from the poodle will travel in little circles, moving up and down in the wave (below [top]), while an object "caught up" in a gravitational wave actually gets stretched and compressed while staying still as space and time are altered around it. In the case of this circle (below [bottom]), you can see how it gets distorted and changes shape.

Note that the points in the circle get closer and further away as the circle flexes, this property is what we exploit in order to detect gravitational waves, but more on that a little later.

Going back to our poodle, the disturbance that a poodle jumping into a lake makes is pretty large relative to the water molecules. The opposite is true for gravitational waves, they are extremely small, though everything creates gravitational waves. Even by typing this sentence, my fingers are creating small gravitational waves, though they are immeasurably insignificant.

Gravitational waves produced by large, energetic events are they only types of waves we have a hope of detecting, because they will warp space enough for us to notice. Some common sources of large gravitational waves are supernovas, neutron stars, or black holes rotating around each other (above) and merging.

Let's move on to the specific gravitational wave the LIGO team detected in late 2015. A little before 3pm mountain time on September 14th of 2015, a gravitational wave swept over the earth, altogether lasting about a tenth of a second. The event that created this wave occurred about 1.3 billion years ago, when two black holes, each about 30 times the mass of our sun (one 36, one 29), began rapidly rotating around each other, then merged. Here are two short videos visualizing the event, one as if you were up close observing it with your own two eyes, and another showing the warping of the gravitational field around the event.

The distortion is caused by gravitational lensing, gravity strong enough to alter the direction of beams of light.

This merging of black holes created a cataclysm in the fabric of spacetime, and the rippling from this event has affected the Earth 1.3 billion years later by compressing it and stretching it by about a nuclear diameter. Here's a short video showing this effect, greatly exaggerated:

<sidenote>

Humans are not good at thinking about scale. Our brains have never needed to be able to comprehend a billion of anything, so evolution didn't set us up to be able to comprehend this sort of number. Thinking in analogies helps, so I came up with this: The same gravitational wave that stretched and compressed Earth by an atomic diameter stretched and compressed the entire solar system by the length of a single skin cell, and the Milky Way galaxy by the distance someone could run in about an hour.

</sidenote>

"How did we detect it?"

Aerial view of LIGO

...by looking very closely at two specific beams of light. The two LIGO observatories in Washington and Louisiana do not look up at the sky, but rather have a very unique setup designed to detect differences in the space between a few sets of mirrors.

Here's how to observatory works:

In the above image, the leftmost element is a really expensive laser pointer.

 - The laser pointer produces incredibly pure light of a specific wavelength (1064 nm).

 - The laser beam hits a half-silvered mirror that splits the beam by letting half the light through and reflecting the other half.

 - Each beam then travels 4km through a vacuum, bounces off a mirror, then travels  4km back to the half silvered mirror at the base.

 - The beam is then recombined and received at a very sensitive detector (H-shaped object near bottom)

A quick not about interference (the "I" in "LIGO"): Light, being a wave, can either "stack up"  or "cancel out." In the image below, you can see that where peaks line up with peaks, the beam multiplies and gets stronger (constructive), and where peaks line up with troughs, the beam cancels out (destructive).

As the mirrors move closer and further apart due to the warping of spacetime, the waves of light align and misalign, making the beam "turn on" and "turn off," as you can see in the animation above.

It's at this I must admit I lied to you. The beam of light pointing at the detector doesn't actually turn on and off, because the warping over a distance of 4km is merely 1/1000th the size of a proton. This is nowhere near enough to warp the mirrors enough to move from fully constructive to fully destructive interference. In actuality, the beam changes by an incredibly small fraction and the change in the brightness in the beam is exceedingly slight. As a result, the instruments that detect the light have to be very precise. While in operation, the LIGO team has had to take remarkable measures to create such a precise instrument. Among the factors that were caught up in the noise they recorded were: individual atoms of gas in the 4km long vacuum tubes, trucks driving on highways kilometers away, as well as quantum effects in the mirrors themselves. That's right, the fact that mirrors are made of atoms was something the team has to consider and remove from their data.

Here is the actual data. The two signals were received 7ms (speed of light delay) apart from each other, and matched predictions nearly perfectly. The confidence level was reported at 99.999994%

One last thing I'll mention.

While reading the paper about the detection, I was struck by this table:

Take a look at the first three items. These are the masses of the two black holes, and the resulting black hole after the merger (M_☉ is solar mass).

There are three solar masses missing.

Einstein figured out what's called mass-energy equivalence (E = mc²), which, at its simplest, states that a particular mass m, say an apple, can be converted into a particular amount of energy, E. Using this equation, we can figure out that our apple contains more than enough energy to form this crater:

Notice the parking lot near the bottom

Using this same equation, three solar masses is the amount of energy released in 5000 supernovae, or to use a common analogy, roughly one million billion billion billion Hiroshima bombs. That's the amount of energy required to make a tiny blip on the screen of a ludicrously precise instrument on earth 1.3 billion light years away.

Cheers,

   - Scott


P.S. - If you turn those waveforms above into audio, you get the sound of a gravitational wave, and it's fantastic:

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Gravitational Waves Supplement

***This is a follow up to the above post about gravitational waves, and no longer directly relates to gravitational waves, but rather is my own personal thoughts and opinions***

The last question - "Why should I care?"

"Until now, we have only seen warped space-time when it is very calm — as though we had only seen the surface of the ocean on a very calm day, when it's quite glassy. We had never seen the ocean roiled in a storm, with crashing waves. All that changed on September 14. The colliding black holes that produced these gravitational waves created a violent storm in the fabric of space and time."

       ~ Kip Thorne 

Something that I hear a lot about science is "what's the point?" Gravitational waves have no intrinsic worth; you cant make money off them in any way. I cede this point entirely (for now). Gravitational waves cant be bought of sold, and in fact the LIGO observatories cost of a few hundred million a year to operate. There are certainly arguments to be made for pure research, such as GPS becoming possible using Einstein's equations, or the fact that Hubble's faulty mirror resulted in software being developed that helped doctors accurately find breast cancer in mammograms. There are hundreds of these examples, but the point I want to make is more nuanced.

Science inspires. I'm continually in awe of what science has accomplished and the ways in which it improves human life. This isn't universal, and any tools developed can be used for moral or amoral purposes, but one only needs to look at nearly any metric, such as quality of drinking water, instances of polio, predictive power of equations over time, overall lifespan etc... and see how it tracks along with the development of formal scientific practices, and you see a fairly strong correlation.

In order to continue this trend and invest in the future, young people need to continue to head into STEM (Science, Technology, Engineering and Math) fields. The best way I know to do that is to continue to make science more than bookkeeping or number-crunching, but to make it engaging and inspiring (think Apollo 11).

Last note - There is a tendency to create a divide between liberal arts and science. This is terribly unhelpful at best and detrimental at worst. Many scientists are not good at disseminating their ideas to the public, and this is something that the liberal arts excels at. Data is not inspiring without the understanding that the liberal arts bring.


Cheers,

   - Scott




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