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Dallin Hatch Shawn Wortham Pearl Corry

Inventors and Their Impact

with Christiaan Huygens (played by Shawn Wortham)

(Dallin): Hello, and welcome to “Inventors and Their Impact”. My name is Dallin Hatch… (Pearl): …and I’m Pearl Corry. (Dallin): …and we will be your hosts for today’s segment/show. The purpose of today’s Podcast is to learn about the 4-stroke process of an internal combustion engine and discuss its impact on the 6 P’s of culture as taught by professor Jackson. In this Podcast, pay close attention to the specific connections we make between the functionality of the combustion engine and its impact on American 20th century transportation. (Pearl): During our integration of the internal combustion engine and American 20th century transportation we’ll pay particular attention to the side effects on the assembly line, development of motels, and establishment of credit to strengthen our argument. To help us make these connections we have invited the original ideologist of the combustion engine, and friend of Dr. Turley, to join us in the studio... (Dallin): So without further ado, please gave a warm welcome to Dr. Christiaan Huygens! [sound of happy children] (Pearl): Christiaan, we are so happy to have you with us and excited to learn from you today! (Christiaan): I am happy to be here Pearl!…

(Pearl): … Well before we dive into the nitty gritty why don’t you tell us a little about yourself. (Christiaan): Yeah sure! As you mentioned my name is Christiaan Huygens and I’m excited to be here on your show today. I was born in the Netherlands in 1629, and lived a good life! As a child I was privately tutored until the age of 16 and grew passionate about mathematics, physics, and astronomy. I enjoyed working in a variety of fields of research and study and would like to think that I made a difference in the world in my profession. One thing most people don’t know about me is that I did in fact design the first prototype of the internal combustion engine, so I’m excited to talk to you guys about it today!

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(Dallin): Wow that is crazy. And I’d say it’s safe to say you’ve had a really large impact! To me there’s no doubt you are one smart dude! (Christiaan): …dude? (Dallin): Uh… never mind, so can you explain to us how the internal combustion engine works? (Christiaan): The internal combustion engine really is a fascinating mechanism—a scientific phenomenon—annnnnd I’ll be honest it’s quite difficult for beginners to understand. I’ll try my best to walk you through a 4 step process that will hopefully give you a clearer picture of what’s going on inside that engine and how it’s able to produce enough energy to turn the wheels of a car for example. Let me just clarify that today I’ll be talking about our basic 4-step process in a 4-stroke combustion engine. That’s a lot of fours! One of the first things that we need to understand is that “all internal combustion engines depend on the exothermic chemical process of combustion.”1 Combustion is the process in which a “complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames….”2 (Pearl): Wait what?? (Christiaan): Oops, sorry Pearl, and thanks for slowing me down. Sometimes I get so excited about science that I forget that I’m teaching! Combustion is a fancy synonym of the word burning. In the combustion engine the basic chemical reaction that’s taking place is the burning of a mixture of a fuel and an oxidizer, which produces a certain amount of energy. In the case of a 4-cylinder engine our fuel is typically going to be gasoline, and our oxidizer is air. So the goal of the engine is to burn that mixture in order to produce energy sufficient to power the machine. Does that make a little more sense?3 (Pearl): Now that’s a language I can understand. So this burning is what causes all the ruckus?! (Christiaan): Oh yeah for sure, that engine is definitely loud once it gets roaring!

                                                                                                               1 "Internal Combustion Engine." - New World Encyclopedia. MediaWiki, 18 Apr.

2014. Web. 31 Mar. 2016 2 "Combustion." - New World Encyclopedia. N.p., n.d. Web. 31 Mar. 2016 3 Ibid.  

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(Pearl): Yeah, I mean, noise levels in the cities have definitely changed over time which could be seen as a good or bad thing depending on your reference frame. But on top of that I think it’s so interesting to see how engines and automobiles have impacted several patterns in our culture such as our patterns of leisure, travel, transportation, business and so much more. The relaxing Sunday drive, travel by way of highway and intercity transportation, the development of and work

in car manufacturing plants, the use of assembly lines, the distribution of vehicles through dealers, and even our pattern of purchasing through credit are all patterns, which have been influenced by the development of this engine! The engine has even changed the way we view our cultures structural time! We saw that reshaped as laws defined when a person could get a driver's license, what kinds of vehicle’s they can operate….. Oh I’m so sorry, I totally got us sidetracked! Please continue, I am anxious to see the science behind it all! (Christiaan): No problem! Now, where were we? Oh yes, the 4 step process! The first step in a process we call induction, or can be referred to as the intake stroke. The intake stroke initiates with the piston being at the top dead center of the combustion cylinder, which is called the cylinder head. A piston is that rod or a disk shaped part, which fits inside a larger cylinder and will actually move up and down within that larger cylinder. That movement is

facilitated by the crankshaft, which is in constant motion on a running engine. You can just remember that the cranky crankshaft is always on the move! Although the piston might look really cool moving up and down, it’s real purpose is to act as a compressor. So the induction stroke is the process by which fuel enters into the combustions cylinder and is then ready to be compressed! What happens is when the crankshaft pulls the piston from the top dead center to the bottom dead center of the chamber, the downward movement of the piston creates a vacuum effect because of the airtight space created by the piston and chamber. To understand why the vacuum is created you need to recognize that on this earth there is always air pressure which is called barometric pressure. As the piston moves down in the cylinder the increased volume within the cylinder creates a cylinder pressure which is actually lower

than the atmospheric pressure which makes it possible for the mixture of air and fuel to come into the cylinder. It might be tempting to think that the cylinder is sucking the air in, but that’s actually not correct. The vacuum which is created actually allows the barometric pressure to push the mixture of fuel and air into the combustion chamber which is just fascinating to me!4 (Dallin): Me too! So, that is what the gas is for! You have no idea how that has impacted my cultural process! Everyday I fill my car up before going to work. That is when I step in the

                                                                                                               4 "Piston." Wikipedia. Wikimedia Foundation, Jan. 2013. Web. 31 Mar. 2016.

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food mart and get my breakfast, and that has been my process nearly every weekday! Also, everyday I am constantly looking at those gas prices, which can completely throw my daily process for a loop! It really slows down my schedule, but the automobile has also sped it up. I guess there is a give and take when it comes to how the car affects cultural process. But what is the cycle after the gas is brought into the cylinder? (Christiaan): The next part of the process is the compression stroke! During the compression stroke, the mixture of fuel and air is compressed by the movement of the piston from its position at the bottom dead center towards the top of the cylinder shaped combustion chamber. As it’s being compressed or pushed towards the top of the chamber, “the proportion of energy which can be extracted from the hot gas” is increased and its capacity to produce power is then recognized at it’s highest potential. It’s important though, that the mixture isn’t compressed excessively. If it’s compressed too much, the mixture can actually be detonated without the spark plug facilitating that detonation which isn’t what you would hope for. Then on the other hand, if you didn’t have enough compression in your cylinder it would cause problems because the current mixture would still be burning when the piston returns to its downward stroke and the exhaust valve opens up which would disrupt the desired cycle. The ideal circumstance is to facilitate a “controlled burn” which is produced by the correct amount of pressure and makes it a much smoother experience for the engine and its owner.5 For example, in your average sedan, the volume of gas to air ratio will be around 50.3 cubic inches. When it is compressed into a 6.3 cubic inch cylinder, that will be something called the compression ratio (50.3/6.3=8). This means that the natural PSI (15) is multiplied by 8 turning the pressure to 120 PSI!6 (Christiaan): Now I hope that’s making sense but let’s just do a quick review in case I’ve lost you both already. The first step is for the fuel mixture to enter into the combustion cylinder which is what we call induction. After the mixture is in the chamber, a piston will compress it towards the top of the chamber which increases its potential energy and prepares it to give off the maximum amount of energy when it’s burned. Is that making sense? (Pearl): Yeah! (Christiaan): Just imagine if horses had that kind of power! I wish that my horses could do that!

                                                                                                               5 "Cylinder Pressure." Performance Trends Inc. N.p., n.d. Web. 31 Mar. 2016. 6 Alves, Francisco Jose. "Production and Feeding of Ethanol Vapor for an Internal

Combustion Engine Operating with Pre-vaporized Fuel." (2007): n. pag. S˜ao Carlos Engineering School of S˜ao Paulo University. Web.  

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(Dallin): It's because you’re giving your horses hay. Next time, try a little gas! (Christiaan): Already tried… poor buttercup. (Dallin): Did you try premium? (Christiaan): NO! *murmur to self* Note to self… try giving Sugarfoot premium gas. Thanks for the advice! Well, let’s move on! (Christiaan): I’m glad you’re catching on because the third step is where things get exciting. After the air and fuel mixture has been compressed up towards the top of the chamber the spark plug ignites and the combustion occurs. The spark plug emits electrical energy when the electrical voltage of an ignition coil gets high enough, Because the fuel and air act as an insulator in the cylinder, no electrical current can flow until the voltage rises above normal.

As the voltage rises, the structure of the gases changes, and once the voltage exceeds the electrical or dielectric strength of the mixture then what happens is the gases actually become ionized and act as a conductor, which allows electrons to flow across the gap and initiate a spark! An average spark plug usually requires a voltage of approximately 20,000 volts in order to fire properly and ignite the mixture. If fired properly, the electrical spark produced by the charged plug will then ignite the mixture which produces heat and energy. The current of electrons will raise the temperature of the spark channel to 60,000 K. It’s interesting to note that just like the piston needs to compress the fuel at just the right amount of pressure in order to produce a successful reaction, the spark plug also plays a key role in

making sure the temperature is just right for the perfect ignition. The temperature of the firing end of the spark plug needs to be kept low enough so that it can prevent any sort of pre-ignition, but it walks a fine line because it also needs to be high enough so that it will actually ignite and prevent any sort of fouling. Pre-ignition is likely to occur if the tip of the firing end of the spark plug exceeds 800 degrees Celsius or 1472 degrees Fahrenheit. A spark plug can’t actually create any heat, they only remove the heat that’s created by the ignition. The spark plug “works as a heat exchanger by pulling unwanted thermal energy from the combustion cylinder and transferring heat to the engine’s cooling system.”7 (Pearl): Wow that’s quite the process! I can hardly believe that! So if I understand correctly… the combustion turns that mass into energy and that is what pushes the piston down and turns the crank shaft? (Christiaan): Exactly, then off you go! Only if I had a corvette back in my day Vroom Vroom!

                                                                                                               7 "How Spark Plugs Work." How Spark Plugs Work. N.p., n.d. Web. 01 Apr. 2016.

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(Pearl): Haha okay, I’ll make sure to draw you one at the end of the show… (Christiaan): BOOYAH! (Pearl): But wow, thanks for the explanation, this whole time I’ve driven my car, I never once would have ever imagined that so much science went into the basic function of it! I guess I’ve always just taken that for granted! (Dallin): Yeah you’re not kidding! I think that’s really amazing to see how so many little parts can end up playing such a huge role! Those little parts all might seem insignificant or just one little part of a bigger process, but their impact is huge and goes far beyond the engine itself! (Christiaan): It’s true! The engine is an amazing invention that has had a huge impact on the world, but before we dive into that, we’ve got to finish wrapping up our engine tutorial with the last step! We’re almost done! The fourth and last step of the combustion cycle is called the Exhaust stroke. Now at this point, we know that the gas has been burned and gives off heat which is harnessed as energy, and that’s precisely the purpose of the exhaust stroke. This is probably the easiest step in the process and possibly the least significant although it does serve it’s purpose. During the exhaust stroke, the piston moves from the bottom dead center back up to the top dead center of the combustion cylinder. As it does so, the exhaust valve is opened and the excess spent or burned mixture exits the cylinder in order to create space for the process to start again and for more fuel to be inducted in, compressed, burned, then expelled! It seems pretty overwhelming at first, but once you get the hang of it then it actually seems pretty logical and makes sense!8 (Dallin): Wow, this is so interesting, now how do you feel now that you know that your idea has had such a huge impact on the world today? (Christiaan): It is exciting, but I also see it put to a lot of evil purposes like war and greenhouse gases…I thought that you were all Christians? (Dallin): Now hold up Christiaan… you can’t going around saying who’s Christian and who isn’t Christian…Christiaan… I’m just giving you a hard time. But on a serious note though, I think it’s so interesting to see the sort of chain reaction that took place over multiple centuries as the combustion transformed from idea to prototype, prototype to invention, and invention to implementation in some of the world's most dynamic and efficient machines. Those engines have been used to power cars, industrial machinery, airplanes, lawnmowers, rockets, and plenty more! We could be here for hours just talking about the impact that it’s had on the American culture let alone the whole world! Let’s take the automobile for

                                                                                                               8 "Stroke (engine)." Wikipedia. Wikimedia Foundation, n.d. Web. 01 Apr. 2016.

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example. It’s pretty safe to say that the automobile has had a significant impact on the American culture and society in the 20th century. It’s unfathomable to think of even trying to measure its influence! So I guess all this talking has raised two questions that I want to ask you in regards to everything I’ve just now mentioned if you don’t mind? (Christiaan): No, not at all! I’d be happy to give my best answer! (Dallin): Perfect! The first I have for you is... did you ever think that your idea of the combustion engine would be developed worldwide at this large of a scale? I mean, could you ever have imagined it becoming what it is today when you first began experimenting with it? The second question I have, and this one is sort of a follow up to the first, but would you be able to expound and help us see some of the ways that you’ve seen this invention impact the American 20th Century’s culture for both positive and negative? I think it would be really intriguing to hear it from your perspective and understand what you are thinking. (Christiaan): You know those are two great questions and the second really deserves a lot of thought and attention. I don’t know that I can give you a perfect answer, but I’ll give you my best shot. In regards to whether or not I thought my idea would ever make it big, that’s really a tough one to measure Shawn. I am very scientifically minded, so it’s easy for me to draw a lot of parallels from science and implement them into culture, so I’m going to try and even take some insight from our combustion engine while we’re on the topic! (Dallin): Yeah I think that would be really interesting to hear your input on that! (Christiaan): So as we look at the combustion engine, we can see how important it is for the mixture to be compressed at just the right force in order to insure the desired engine functionality and behavior. If there’s too much or too little pressure, you’re just not going to find the right results and eventually see the engine function how you would hope. Then we have the spark plug—which also has to learn to find and be at just the right temperature in order to ignite the fuel properly. Likewise, as a Scientist with so many ideas and theories, I felt a similar sort of pressure that I think many people face today. We all want our ideas to be just right and produce the desired results or make it big and that’s frankly just hard to predict sometimes. Not only is it hard to predict, but it’s nearly impossible to measure the rate at which an idea will impact, penetrate, or change any given culture. See in science it’s easy for us to measure things. So to answer your question, I can’t say I ever imagined one of my many ideas going so far and having such a huge affect on the world. One of the things I definitely didn’t predict was how the automobile would become part of the world of fashion. As a product the automobile has transcended utility and become entrenched in the world of design. A car can be a symbol of social status, depending on the brand and/or make. Luxury brands such as Mercedes-Benz, Lexus, Ferrari, and BMW, are typically seen driven by those of a higher social class whereas the more economical vehicles like Toyota, Chevy and Honda will be found driven by a large variety of Americans and transcend across

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multiple social classes. The luxury cars will generally have more cylinders in their engines, which makes them run more smoothly than other cars. The ideal car has a great deal of force in addition to it’s visual appeal--just like a strong idea has to come nicely “packaged” in order to receive attention from the leaders who can then turn it into a reality. Pearl: I’ve heard that the most popular car color is white. But it’s crazy how cars come in almost every color imaginable!9 (Dallin): And now comfort and safety are priorities as well. Because of improvements to vehicle safety (according to the US Department of Transportation), “[it is estimated] that improvements made after the model year 2000 fleet prevented the crashes of 700,000 vehicles; prevented or mitigated the injuries of 1 million occupants; and saved 2,000 lives in the 2008 calendar year alone. Of the 9 million passenger vehicles that were in crashes, the crashes of an estimated 200,000 of them were preventable by improvements to the model year 2008 fleet.”10 (Christiaan): It’s great that the car has become a trusted product that allows people to get things done with ease and speed, all while looking great—BUT, what about the environmental impacts? I sometimes wonder if my invention was worth all the pollution I’ve heard about. (Pearl): It’s true that pollution from cars has been very harmful to the environment. The USA union of Concerned Scientists has reported that, “collectively, cars and trucks account for

nearly one-fifth of all U.S. emissions, emitting around 24 pounds of carbon dioxide and other global-warming gases for every gallon of gas. About 5 pounds comes from the extraction, production, and delivery of the fuel, while the great bulk of heat-trapping emissions—more than 19 pounds per gallon—comes right out of a car’s tailpipe.”11 That means that most of the problem stems from that Exhaust stroke that was explained earlier. (Shawn): The good thing is that Americans are become more aware of this issue and have taken measures to

reduce emissions from cars. Better materials are being used to create engines that will last longer. This means people keep their cars for longer periods of time. Jagadish Sorab, technical leader for engine design at Ford Motor, cites what is happening in California as an

                                                                                                               9 “Car colour popularity” Wikipedia. Wikimedia Foundation, n. d. Web. 01 April

2016. 10 "An Analysis of Recent Improvements to Vehicle Safety." Annals of Emergency

Medicine 61.2 (2013): 222. Web. 08 Apr. 2016. 11 "Car Emissions and Global Warming." Union of Concerned Scientists. N.p., n.d.

Web. 08 Apr. 2016.  

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example: “The California Air Resources Board and the E.P.A. have been very focused on making sure that catalytic converters perform within 96 percent of their original capability at 100,000 miles. Because of this, we needed to reduce the amount of oil being used by the engine to reduce the oil reaching the catalysts.”12 (Christiaan): I’m glad to hear that. Culture must be infused with an awareness of how science affects our relationship with the earth—and with each other. Speaking of interacting with others, one of the most interesting cultural products that I’ve heard about that is a direct result of the development of the automobile is the quintessential Motor Hotel, or Motel! I imagine you’ve heard of those? (Pearl): Yeah my dad makes us stay in one every time we go on a family road trip! It’s definitely a whole lot better than sleeping in a tent, but they can be really a hit or miss! (Christiaan): Yeah I believe it! I saw a few of those while riding my horse across country last year, but what I didn’t realize is that “motor hotels or motels are specifically constructed for the automotive world. They are designed to provide overnight lodging for cross-country drivers. The first motels started being made in 1925 and they can mainly be found by busy interchanges, the outskirts of towns, or near airports.” They host, entertain, and provide other great services for travelers all around the country and anybody that’s been on one of those cross country trips has definitely benefited from their services! The great part is that local business owners benefit as well and it ends up working out really well for everyone! One of the really nice things about it is that “all motels have free parking near the rooms, which allow guests to reach their rooms directly. Most motels do not require reservations because most traveling motorist do not exactly know where they will stay that night. For motorists' convenience, motels have large signs that tell whether or not there are any vacancies. Nowadays, one sees more motels than hotels.”13 Then there was a striking development of drive-in businesses, again first in the United States but spreading rapidly everywhere else. The Pig Stand in Dallas, Texas became the first drive-in restaurant in 1921 when they modified their parking lot to allow people to order their food and eat without leaving their cars. Then came drive-in-movies,

                                                                                                               12 Ford, Dexter. "As Cars Are Kept Longer, 200,000 Is New 100,000." The New York

Times. The New York Times, 17 Mar. 2012. Web. 08 Apr. 2016. 13 "Impact of the Automobile on the Economy." The Impact of the Automobile on the

20th Century. N.p., n.d. Web. 01 Apr. 2016.

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drive-through banks, and convenience stores. In 1946, 7-11 opened and became the first extended hours convenience store open for local homeowners and cross-country travelers.14 Now when we began talking science today, I’m sure the last thing that you thought we would get to would be economics and finance, or the impact that the combustion engine would eventually have on the business world as automobiles manufacturing, maintenance, and

marketing took off in America. It would be quite literally impossible to list all of the detailed specifics of the effects it has had, but there are a few especially significant effects that we’ve seen as a direct result to the auto industry and its impact on business. “In 1916, the marketing of automobiles stimulated a great expansion in the use of "credit." Installment buying existed before the automobile but only for a limited range of products. Manufacturers of medium- priced cars allowed customers to pay in several payments to

help jostle the competition of the low-priced Model T. Installments became a universal practice in all countries in the purchase of automobiles, and it accustomed people to buying other durable consumer goods in the same way.”15 (Dallin): So if I’m understanding you correctly, what you’re saying is that the credit card I use daily, really got it’s start by the automobile industry? (Christiaan): That’s right! Isn’t that amazing? And it really doesn’t even stop there! Pearl, do you by chance remember what made Henry Ford so successful? (Pearl): Well yeah, didn’t he just make them really cheap? (Christiaan): That’s part of it! Henry Ford was largely successful because of his development of the assembly line which allowed him to produce a lot more cars for a lot cheaper price and even do it a lot quicker and more efficient! The assembly line made a huge impact in the work patterns of those employees and we began to see assembly like patterns all across the world in the industrial revolution. One of the industries that you might not have anticipated to follow the example of the automobile’s assembly line, was actually the food industry! “Ray Kroc took the assembly line idea into the food industry when he started opening multiple McDonalds fast food in 1948. This triggered something that caused a major commercial

                                                                                                               14 Ibid. 15 Ibid.

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growth in our nation's food industry. Fast food and other chain restaurants started opening everywhere in the world.”16 (Pearl): So one of the most interesting things I’ve picked up on from our conversation about the combustion engine is how it has become less visible or less present in people’s minds as it has evolved to do its job better. Cars are now just as much about “their people” as they are about their mechanics. In fact, some people name their cars as if they are pets or friends. People like to “match” their cars. (Dallin): It’s amazing to me that something that was once a novelty is now considered a necessity in American society. Most people learn to drive--it is considered an important skill, both in daily life and in emergencies. (Pearl): Yeah, just think about police cars, fire trucks, and ambulances. Emergency responders rely on the power of the combustion engine to reduce the mortality rate in America! (Christiaan): I’m sure a lot of the people they rescue are crazy teenagers! Isn’t the age at which people can get drivers licenses lower in America than it is in many other countries? (Dallin): Sure is. And for many teenagers, learning to drive a car/having one’s own car is powerful-- a symbol of freedom, of growing up. (Christiaan): Funny that a symbol of freedom in America could come from a 17th century Dutch inventor!

(Pearl): It is amazing how this world works. On that note, what an honor it has been to have you on our show Christiaan! (Christiaan): The honor has been all mine Pearl. (Dallin): Christian, you have taught us how the engine works, and how it has had an impact on our culture today. Your insights have been extremely helpful, and who would have known that there could be such an amazing connection between the two. Thank you! (Christiaan): It really has been a pleasure. I must get back to my time. Sugarfoot is waiting at home and I still got to stop at Maverick before I go back to the 17th century. (Pearl): We understand, well thanks for joining us for “Inventors and Their impact”. I’m Pearl Corry… (Dallin): … and I am Dallin Hatch. (Pearl): And we hope to see you next time.                                                                                                                

16 Ibid.

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(Christiaan):... (pause) where is my corvette?!?!

(cut)      See  page  following  for  image  sources.                                                                              

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   Images:        Fig.  1:  “Portrait  of  Christiaan  Huygens,  oil  on  canvas,  XVII  century,”  from:  http://www.astronomie.nl/wwwdata/spspIMG259.jpg  (public  domain)    Fig.  2:  From:  http://www.canyon-­‐news.com/brush-­‐fire-­‐in-­‐malibu-­‐caused-­‐by-­‐fatal-­‐crash/29586  (public  domain)    Fig.  3:  From:  https://commons.wikimedia.org/wiki/File:80_MPH_Speed_Limit_in_Utah.jpg  (public  domain)    Fig.  4:  “Animated  scheme  of  a  four  stroke  internal  combustion  engine,  Otto  principle,”  from:  https://commons.wikimedia.org/wiki/File:4StrokeEngine_Ortho_3D_Small.gif  (licensed  under  creative  commons)    Fig.  5:  see  above    Fig.  6:  see  above    Fig.  7:  see  above    Fig.  8:  “Ferrari  488  GTB  at  the  2015  Shanghai  Auto  Show,”  from:  https://commons.wikimedia.org/wiki/File:Ferrari_488_GTB.jpg  (licensed  under  creative  commons)    Fig.  9:  “Automobile  exhaust  gas,”  from:  https://commons.wikimedia.org/wiki/File:Automobile_exhaust_gas.jpg  (licensed  under  creative  commons)      Fig.  10:  “High  Desert  Motel  in  Joshua  Tree,  California,”  from:  https://commons.wikimedia.org/wiki/File:High_Desert_Motel,_Joshua_Tree.jpg  (licensed  under  creative  commons)    Fig.  11:  From:  https://commons.wikimedia.org/wiki/File:Credit-­‐cards.jpg  (licensed  under  creative  commons)    Fig.  12:  “A  new  McDonald's  restaurant  in  Mount  Pleasant,  Iowa,”  from:  https://commons.wikimedia.org/wiki/File:New_McDonald%27s_restaurant_in_Mount_Pleasant,_Iowa.jpg#mw-­‐jump-­‐to-­‐license  (licensed  under  creative  commons)    

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Fig.  13:  “An  American  Medical  Response  ambulance  in  Redwood  City,”  from:  https://en.wikipedia.org/wiki/Redwood_City,_California  (licensed  under  creative  commons)