Monday, January 9th, 2012

Transcription

1 Partially Edited Class Transcripts for Physics 101 (Instructor: Micky Holcomb) I have not had time to read everything, so there could be some errors in the text. Monday, January 9th, 2012 Professor (regarding ungraded survey for class improvement): As you fill out these sheets, do it exactly as you see it on the screen. Use your 700 number, but leave the left hand space blank. This is a 42 question survey about your opinions of physics. Answer it as honestly as you can. Follow the instructions on the screen on how to fill it out (students fill out surveys) If you are done, check the following things for me. Make sure you have left the leftmost ID number blank. Make sure you have bubbled in your 700 number below. You don't have to fill in a bubble for the leftmost blank. Make sure you have answered 42 questions, not 40. Two questions are on the back of the page. My name is Micky Holcomb. You are in Physics 101. This is section 1. The first thing I like to start with in this class is, What is physics? In order to encourage you to think about that question, let's say you ran into someone at a party and they said they were doing research in physics. What might come to your mind? Or, what might come to your friend s mind? I would like to hear some responses. Just shout them out. What might they work on? Male Student: Gravity. Professor: Gravity, yeah. That's good physics. We will talk a lot in this class so you will have to get over shyness. Female Student: Math. Male Student: String theory. Professor: We will not talk about that in this class. That is hard stuff. Some of the stuff in this class is easy once you get used to it. It takes practice. Physics in Greek means nature. This is natural science. We are talking about

2 matter and its motion through space. I am moving through space now. I am moving through time, too, even if I m standing still. What is force? How do I quantify that? How do I put numbers to it? Why would I want to apply force to it? Sometimes an estimate is all you need. If I am going to a grocery store, I need a rough estimate to make sure I have enough money in case I forget my credit card. When I do my taxes I need exact numbers. The government doesn't want me to estimate. Sometimes you need an exact answer. A calculator is useful. Please, bring them to the exam. Broadly, physics is our analysis of the world around us, how the world and universe behave. Physics has some subcategories. We will not get into all of those. I have color coated those. [On overhead.] Those in green we will touch on in this course. Mechanics, thermodynamics, understanding heat. Acoustics, why can you hear me in the back? Can you hear me in the back? Optics. Fluid dynamics, probably the most important field of physics of you are in the medical field. It has applications like blood flow in your arms. In 102, the subjects in red will be relevant. The three bolded subjects are those that WVU has expertise in. I focus on solid state physics. We will talk about what that is. We have discussed many of the ideas in physics out there. Why should you care? Why would one study physics? I would make a bet that each one of you in this room is here because you are required to take this class. I am aware of that. Why? Why do you think you are required to take this class? Male Student: Relevant to your major. I am in forensics. Professor: Lots of physics in forensics. I love it. And in the medical field, too. What if I am taking history? Why do I have to know physics? Or some other major that might not seem obvious for why physics is necessary? I need a volunteer. I need someone who has already had a bad day on the first

3 day. You might have been late, the PRT broke down. I heard someone say that. Female Student: I will do it. Professor: Come up. This is the best thing you have volunteered for. Why should someone take physics? Make sure I picked out the right cell phone, not my current phone. This is my previous cell phone. I am not happy with it anymore. I like my new one. This is a hammer. You can apply as much force to that cell phone as many times as you like! Do it some more! Alright! Good job. What is your name? Female Student: Savannah. Professor: Give Savannah a hand. Let's see what we have. This needs more banging. Someone else want to take a try? Someone in the front? Come on up. Give it a few. That is good. Thank you. Why have I done this? Male Student: Feels good. Professor: It does, I have to say. What does my mangled cell phone have to do with why you should study physics? Male Student: You have to know what force to apply to break the cell phone. Professor: Good one. I didn't think of that. You don't have to know though. I could hit it a lot. If there was an athlete or someone really muscley in the class, they could just slam it. Male Student: You could look at the surface area of the hammer, and use the other side to do more damage. Professor: Great answer, though not the ones I was thinking of. I was thinking we would do a little more damage. All of the components inside of the phone are due to physics. How the phone is used to communicate with other

4 cell phones is due to physics. It has memory, how I save Angry Birds on my cell phone. The memory is due to physics. Transistors, which relate to computers too. Physics has improved this. These components are all from physics. Physics is not limited to cell phones and computers. It is all around us from acoustics in this room to our refrigerators at home. People used to use blocks of ice to refrigerate food. All of the things that make our lives more efficient. Many of those things are from physics. For example, the internet, which hopefully you are not browsing at the moment. It was once called the NSF Net. NSF, National Science Foundation. They gave us the internet, not Al Gore. How many jobs has the internet created? People focus on communication over the internet. Google, lots of great industry. For those of you interested in the physics of cell phones, I have a link. If you are interested in other cool things science has created, I have a link at the bottom. That is not the point of this course, but I want to encourage you that if you think you will never use physics in your life or the skills you learn here, it is useful to know that physics makes our lives better. It is a cool talking point at parties. It was fun to smash the cell phone though it didn't go in as many parts as I wanted. Why study physics? It does all kinds of cool things. It is cool to the professor in the front of the room, but why are you required to take the class? It is a basic science applied to other fields like forensics and medicals fields. You get marketable skills for your future career. You problem solve with limited information applied. Will I be able to smash this cell phone to smithereens? Guessing, how to see a situation. We will talk about this in class. For example, I have a very sloped driveway, about 20 degrees. In winter, it gets very icy and difficult to get out of. We will do some guessing if we can get out of the driveway or if we will cancel class. I won t cancel class, by the way. I can get out, so that will not happen. It is not easy, though. It is also good to know what a physicist does. I am a professor. There are many kinds in different industries, etc. In previous classes, because this is so important, I had everyone interview a scientist. One person said that they were so dreading the assignment that they put it off, but then they found it cool that the scientist they interviewed was relevant to their field and career.

5 We will not do that this year, but I want to touch upon what I do as a physicists. One of the things I do is I teach class. That is supposed to be 40 percent of my job. What else do I do? Female Student: Research. Professor: I am to perform cutting edge research and manage the students who do it. I do some myself, not as much as I like to, but that's OK. What the heck am I doing in my office? Anyone? I write papers in scientific journals so I can report on what interesting knowledge I gain. I have to get funding for my research. It s not cheap. I have a cool laser system in my lab that costs more than my house. I have to justify why my research with that expensive laser is worth it. What cool stuff am I adding to mankind to justify spending basically a house on this? I present research a lot. By this point in my career, I am comfortable talking to so many students. That was not always the case. I will miss classes sometimes. I will have a sub. I will let you know ahead of time. I do a lot of services and meetings. I sit in on qualifiers where students defend their PhD research. I sit on committees to get recruit new students and faculty. Committees to make classes better. I teach a seminar on work life satisfaction. This tells how to balance life and work in science. Great if you want to do tons of work. Not everyone does. I write a lot of reference letters. Keep that in mind for grad school. And I do a lot of outreach. I am busy on top of taking care of my little ones, a two year old and a 9.5 month old. [On overhead.] The next question I get once I have convinced you that you should be taking physics because it is useful to you and that physicists do more than teach classes is, isn't physics hard? Why? You have all heard this, that it is hard. Why do you think physics is hard? Female Student: Math.

6 Professor: That is a frequent concern. Anything else? I often hear, of course not about myself [joking], that the professors are awful. Female Student: Applications. Professor: Right. Not everyone is good at relating physics to real life. Blocks on inclined planes. You see that a lot. We will do that. You have to understand why it is useful or you will not care. The biggest concern is math. There are a lot of formulas to learn. Common concerns that I will address. In this class, you do not have to memorize formulas. They will be on the exam. It is already on the course website, which I will give you the address for later. You can practice using those formulas right now. You can use a calculator. I discourage the use of graphing calculators because people do funny things with them. If you bring to the exam, I will have an extra close eye on you. But, that is fine if it is what you have. Just be aware. Physics does have a lot of math. You must have a basic knowledge of algebra for this class. We will review trigonometry a couple times in this course. If you can move factors from one side to the other, subtract from both sides, etc., you can handle the math in this course. I know that at least 98 percent of you are really good at this stuff. You can do it. You have gotten into college. You are doing this stuff all the time. If you struggle, you will have to make an extra effort to remind yourself of these math skills. We will not focus on algebra in this class. We are interested in physics. If you are struggling, see me in my office hours My teaching philosophy: You often see teachers looking for the ideal student. This is my depiction of the ideal student. [On overhead.] This girl is ready to learn. She has funnels in both ears and is ready to absorb all of the information there is to learn. Do you see her in this room?

7 The student's view of often a little different. They think the professor has the funnel upside down. Or you have your funnel way back there and I am not getting it to you. If I could poor knowledge into your head, I would plug my hard drive into you and we would be done. One day we will have hard drives in our brain. That would be cool. It is not that simple. We have to work together to transfer knowledge Have you heard of Bloom's Taxonomy? This is a pyramid that describes your understanding of a topic. The bottom of it is the simple knowledge. You can tell me dates, numbers of things. Next is understanding that. Then evaluating and planning. This class is not about the bottom level, remembering. If you have a photographic memory, it does not mean you will get an A. You have to understand and apply the knowledge in the book. That takes a lot of practice. You have to solve problems and you learn that by starting to solve them. If you don't know how, look at how other people did it. I will give you extra problems in each class. The people who do the best in this course do extra beyond what I require for a grade. Keep that in mind. To do well in this course, you have to do a lot of practice problems. I know you need A's for your future careers. I get that and I give a lot of A's, but you have to work for it. These extra problems are how you will get there Also, one thing that is difficult about this course is that it covers 13 chapters. That is a lot of information. I can't avoid that. Another thing to help you move up the pyramid of learning is repetition. How many times do you come across the same information? Since we cover 13 chapters in 15 weeks, we can't repeat chapters. How can I force reputation, which is how you learn best, though we have to cover a lot of material? We will do this through some steps. You have to increase the difficulty of the material, too. First, read the material before coming to class. In the syllabus is a teaching schedule that I am good at sticking to. Read those sections before class. I was a student once. I didn't always read the material, so I have to enforce it sometimes. There will be quizzes in class that are not announced. Generally they

8 are one or two questions. I will use clickers. We will talk about that in a minute You will have homework between each class. Only one or two problems on Web Assign. If you get the correct answer before 11 am, before class, you get an extra 10% extra credit on that assignment. The first homework is due Friday. We will have lecture, talk about and discuss it. Then you will go back and finish anything you didn't finish. Then you will review and be tested. This is much repetition. I hope you learn a lot by the end of class. I want to set up some ground rules. In this class, it is most important for you to be respectful to your fellow classmates. Ideally, me too, but more importantly each other. What does that mean to you that you are respected in this class? I thought of one thing, that it is nice that there are not distractions in the class. What distracts you? I don't have ground rules that I set. But if there is something important to you, I want to set them now. Chatter is frequently a distraction. Anything else you want to bring up? If you have any distracting things going on your computer. Some people are taking notes and that is fine. Anything distracting we can avoid? This is your chance to say to the other 179 people in the class, don't do this so I can learn this material. I want you to participate in questions. I have encouraged you to discuss things. I want your participation. I have office hours on Mondays and Thursday at these times. If they don't work, we can set up an appointment. The course website is on here. It is on the syllabus. This is what it looks like. [On overhead.] Homework due between each class. I have made the due time midnight, a minute before. When you log into Web Assign, which we are using for the first time, insert this code. Click I have a class key and insert the code [From overhead: wvu ]. Use your name from MIX so I know who you are. You need a clicker. This will work for any class you need from now on that uses them. I think it costs 40 dollars at the book store. You can use them for any classes that use clickers while you are here. No labs this week.

9 Wednesday, January 11, 2012 Professor: Let's get started for today. We have a lot to cover today. This is the only class this semester where we will actually cover a whole chapter. We will try to cover all of Chapter 1 today including all of the basics behind doing some of the math needed for this class. The reason we can cover a whole chapter is that I hope you have seen this stuff before, but if some of it is really new and the lecture doesn't help, I encourage you to do extra practice. I will have extra practice questions for each class. I encourage you to do these even if you aren't struggling. One thing you don't need today but you do need next week is an I-Clicker 2. We will be doing clicker questions, some of which will be graded. Some will be anonymous. This will help with class discussion and will help me know what you understand and how many of understand. We will discuss after these questions. Sometimes I will ask an easy problem. I don't always know if the problem is easy or hard when I ask. By polling, I can get an idea of how many get the right answer. If 70 to 90 percent get the right answer, we don't really need to discuss it. If there is a lot of division though, people having different answers, we may have to discuss it in class. To receive credit and do this registration, you have to bring your clicker to class and vote on something before you register. You will synch it with a machine that I am going to bring Friday. You don't have to register immediately, but I want you to register this month or I have to go back and relink names with answers, which becomes inconvenient quickly with a class this size. For these clicker questions, since the main point of doing them is for us to discuss material and review concepts, the majority of credit is for just putting in an answer. 80 percent comes from just answering. I have to know if you understand what I am asking. 20 percent is for the right answer. That is the bonus for those who understand the material. Any questions about I-Clickers? I may have the system Friday, but I will not grade that. We can test them Friday, but we will not have grades Friday.

10 In each class, the first five minutes of the class will cover the most important things from the last class. [On overhead.] You saw this in the last class. The majority of the class information can be found at the website found above. This is a screen shot of what that looks like. All previous lectures are online under the lecture tab on the left. I will not be able to put up lectures before because we will do polling questions and it is unfair for people to see the questions first. The lectures will look exactly like what you see on this. About half of you have signed up for Web Assign. Homework will be due after each class starting Friday. You have to have this course code when you log in. There is a link on the class website under additional materials that sends you to a first time log in screen. I added that for convince. You were asking (before class) about a ten percent bonus on homework questions. For questions that are not opinion questions, like I will ask about what you are confused about, but if you get the correct answer before class, you get a 10 percent bonus for that part of the question. You could get part of ten percent for the question or all of the points if you do the whole assignment right before class. Any questions? Female Student: For the first homework, we have to finish it for Monday? Professor: Yes. The reason I am offering extra credit as we talked about Monday is that I am trying to encourage you, to force you, to read ahead of class. The point is that the more times you see the material, the more likely you are to understand it, and I can come in and focus on the confusing points if you tell me. I will ask you frequently what you don't understand from the homework. If 20 people say the same thing, I know I have to talk about it today. Please answer those. Since I ask that question on each homework assignment, I know you will sometimes get it. It is fine to write "none." I didn't have any problems. Thinks about it. List it if you have any issues. This is the opportunity to get input on the next

11 lecture. I take those very seriously. There is no lab this week. I also had some people ask about the manual. I have been told that your lab TA's have an electronic copy of the lab manual that they will give to you. I don't know who your lab TA is. I get this question each semester. If it is not obvious, go to 111 White Hall for help. Another note about I-Clickers. I wanted to show you what Web Assign looks roughly like. [On overhead.] This is my version of it. You will see two assignments now if you go there. There is a test assignment that you don't have to do if you don't want, but it helps you understand Web Assign and has good questions from Chapter 1. The one labeled is the homework due at midnight. The means to read sections 2.0 to section 3 in the book. I will do that with each assignment so you know what is being covered. Female Student: How many attempts do you get? Professor: Ten. Though, I think I have 50 for the test assignment. Female Student: Is credit taken off for each attempt? Professor: No credit is taken off for attempts. You can ask for extensions on assignments. I consider those and may give them. If people frequently use them, I may stop giving them. You can ask for an extension on the due date or how many submissions for the assignment. Any questions? Since the first homework is due Friday, register soon. [On overhead.] The test assignment looks something like this. There are units after these text boxes. These are the units they are asking for. The submission button is at the bottom. [On overhead.] There is a guide at this link for help answering questions. I think Web Assign has its own test assignment for you. Web Assign is free for two weeks. That gives you time to try it out and see if you

12 will stay in this section. I encourage you to do this practice problem because it helps you understand Web Assign formatting, etc. Today we will talk about the scientific notation. [On overhead.] If you have a long number like this one, it is often inconvenient to write it in this manner. You can write it in scientific notation. You can take the number of significant figures. The 24 in this example represents the number of times I moved my decimal point in this example. You can count over how many places I had to move the decimal point. That is scientific notation. Web Assign writes it differently. Instead of writing ten to the ten or whatever, it will see a formatting issue. It wants to see a number like 6.328e24. That means the same thing to Web Assign. You can also write it out. I want to caution you that your calculator does not use "e" for the same thing. That is exponential. A double EE in caps does mean to the power of what you write after it. Don't mix up the exponential function on the calculator. On your calculator, if you have a double E functions, you will frequently have to hit shift, second or function to get it because it is not often used by people. Why do you think we don't use this double E function very often? We don't deal with really big numbers or really small numbers often. We could have 6.4 times I would move the decimal the other direction three times. The plus or minus tells the direction you move the decimal point. If I move it 1, 2, 3, I have to insert zeros here. I get for that example. Scientific notation is for really big or really small numbers. We don't frequently deal with really big or really small numbers. Why? If we did, it would be inconvenient to write all those out. If something is inconvenient, eventually people change things. People don't like inconvenience. One thing you could change potentially are units. We will talk all about numbers. You can convert from an inconvenient unit to another. In Web Assign, units are always given as part of the answer. You want to make

13 sure you are using the same units that they are using. Common mistake. I also did set up a Facebook page for this class. This is my first time and I am not an expert Facebook user. This lets you discuss the topics in class. You can discuss strategies for homework. I don't want you to share answers. I won't check it regularly. I will check sometimes. This is for you to help each other. I have learned through teaching that you don't learn a topic until you teach it to someone. This is a great experience teaching other people and seeing what others have issues with in the class. This is an experiment. I believe you can just search for the group and add yourself. We talked a little bit last time about what physics is. We talked about it as the science of nature. More specifically it is the discovery of the principles of nature, not just understanding nature. What does discovery imply? It means you are figuring something out that has not been figured out yet. Are we discovering things in this class? You maybe didn't know it before, so it is a discovery for you, but not for the world. How do you figure out how to discover things for the world? How do you know what was discovered already? You take a class like this and learn it. That is how you practice. It is not easy to discover things. You have to practice, problem solve. You have to have a problem that nobody can solve and apply a strategy to figure it out. To do that, you practice on things that people have already done. When you get stuck, you see what they did. You get better and better over the time. That is the goal. We are going to discover about nature in this class. The discovery process uses the scientific method. I observe something, like I am ten feet or some distance from that wall. I develop a hypothesis, that I am 10 feet from the wall. Before I said roughly ten feet, I don't know. Then what do I do? I have to test it, right? I have to go experiment. My experiment will confirm or deny by hypothesis. I was supposed to have a meter stick in the class. That is OK. I could take a meter stick and measure exactly how far I am from the wall. Would I be exactly right? Unlikely, but I could be close.

14 By doing these experiments, we use some tools. I just described length, the distance from myself to the wall. Others are time, mass - how much things weigh. We will talk about this in class. In each class I will have a slide like this after our review of the last class. It will have some practice problems on the bottom. These go beyond the homework. You don't have to do them, but I encourage you to if you are struggling. All of the odd problems in the book have answers in the back. Once you figure out the problem and do it, you can go see if you got it right. I will also talk about what concepts we will discuss. We will talk about units and why they are important. We will talk about how to convert between units. We will talk about estimating and its importance. We will briefly discuss significant figures. If we have time we will talk about trig. If we don't, we will talk about it at the end of Chapter 3. We will not talk about dimensional analysis. It is a good section if you want to read it. We don't have time today to look at it and it will not be on your test but, it helps with parts of physics. Pretty much anywhere in the world except in the US and in England, people use the metric system. You will have to a lot of conversions between the metric system and the system we are used to. The metric system is the language that physics uses. For example, length is measured by meters. That is 3.28 feet. I don't expect you to memorize that number. It will be on the test if you need it, but you should be able to covert with the equivalency between the two. Mass is the measurement of weight and it is in kilograms. That is the standard unit. One kilogram is 2.2 pounds. The number of kilograms that I weigh is smaller than the pounds I weigh, which is too much. Time is in seconds. That is the standard unit for time. If you had an hour, like when we talk about velocity, and people talk about going some miles per hour, you have to covert that to seconds. There are 3,600 seconds in an hour.

15 We also see miles per hour. Are miles a standard unit? No. We will convert that, too. We will practice that. We already talked some about scientific notation. [On overhead.] This is an example. I can also write this as 4,500. Instead of writing a big number like this, we often add prefixes. Instead of 4,500 meters, we could add a prefix and say 4.5 kilometers. Kilo means a thousand. I could divide this number by a thousand. I can times this by a conversion factor. [On board.] I can get rid of meters and get kilometers. There are 1,000 meters in 1 kilometer. Now these meters cancel out and I am left with kilometers. I divide 4,500 by 1,000 and get 4.5 kilometers. This is a strategy of converting units. It applies to everything. [On board.] I could also do it like this. Let's say I wanted it in feet. I could multiply this. I will have feet on top and kilometers below. We knew there are 3.28 feet in a meter. Let me do it in two steps feet in one meter. I have weird units now because things don't all cancel out. I have a thousand meters and one kilometer. I can cancel these out. [On board.] If I multiply 4.5 by 3.28 by 1,000 that is the number are feet. This is a standard way of converting units. If you are struggling, practice. Then come see me in office hours. You need this over and over in my class. There are 100 centimeters in one meter. There are 1,000 grams in one kilogram. Conversion of units. We will do that a lot in this class. It is important to include units in all answers. Web Assign gives you the units. But that will not be the case on the test. Write down units or I have no idea what the number means. I will not assume you mean the right thing. I will deduct a point. I give partial credit. I don't take off full credit for something small. Let's say you are told that a car is traveling at 28.0 m/s. Is that fast? You have no idea because you are not used to these units. We have to convert it. What will we change meters to? Male Student: Kilometers.

16 Professor: We could, but we don't really know what kilometers per hour are either. We want to get it into miles. And then seconds. We are used to miles per hour, so we will have to do that, too. We have a couple steps. Let's start with meters. It doesn't matter the order you use. [On board.] Just like I did on the board here for this problem, and this is a conversion number I don't expect you to know. In one mile is 1,609 meters. You don't have to memorize it. I will give it to you. I hate memorization. I was good at it when I was younger. [On overhead.] We have it in miles per second. I will multiply by 60 seconds in a minute and 60 minutes in an hour. If you cancel the units, you get 62.6 miles per hour. That is a reasonable speed on the interstate, but not in a school zone. If you are struggling with conversions, practice and you will get better. Why is this important? I like to give this example. There are news stories about cases gone wrong. NASA likes to let a business take care of some of their work. They asked Lockheed-Martin to do some work for them. They did the problem right, but gave back some non-metric answer and didn't include the units at the end, so nobody caught it. NASA didn't try to blame Lockheed-Martin. They were nice about it. They said that a single unit error should not bring down a big mission. The orbiter changed its distance so much that it crashed into Mars. It cost 125 million dollars and a unit mistake brought it down. A stupid mistake shouldn't bring down a whole mission, but it can happen. One more example. One of you is studying abroad. You find an apartment in Europe. You find an ad and the size is listed in meters. This example is 90 square meters. I need to know square feet and know if it is a big apartment. We are starting with 90 square meters. You would frequently take length and width and multiply to get square meters. I have to convert again. How many feet are in a meter? I have to do that. Am I done? Can I use the calculator now? No. I have canceled one meter, but not both. I have to do it twice. Another way to write that is 90 meters * (3.28

17 feet / 1 meter) 2. The square implies that you are squaring meters, but concealing these out. You have square feet. That is 968 square feet. Is that a big apartment? Big for Europe. In California, I had a two bedroom apartment that was pretty spacious. It was about 800 square feet. The next thing to talk about is order of magnitude calculations. Frequently an exact answer is not necessary. You will know when it is not necessary for me because I will ask you to estimate something. If I don't ask you to estimate I want as exact an answer as you can get. This is useful when you need an answer that is just pretty close. I mentioned an example Monday of being at the grocery store with 50 dollars and no credit card. You don't want to overspend. You could estimate as you go along. You need a rough answer. Maybe you give yourself a buffer of ten dollars for tax. Whatever you want to do. That is just an example. When you estimate things, your uncertainty is very large compared to me measuring with a meter stick from here to the wall. That is a small amount of uncertainty. I was estimating when I said ten feet. Does it matter if it is 9 feet? You guys don't care. Let's estimate the height of a person in meters. I want a rough answer. What is a good estimate of the height of a person? I am hearing a lot of twos. Converted, that is about 6.5 feet, larger than the average height of a person. But is it close? It is fine for an estimate answer. If I didn't ask for an estimate, that would be a little high. How about the average weight of a person? There are 2.2 pounds in a kilogram. It depends on what you think the average weight of a person is. 80 kilograms is 186 pounds. If someone answered instead 100 kilograms for the estimate, would that be wrong? Is 100 wrong for an estimate? No. It is not wrong. It may be less accurate, but it is a good estimate. You are looking for things within a factor of ten. If I was doing this with groceries I would say that five is close to 50. They are really far apart. Estimates are not fine for the path of a Mars orbiter.

18 How about the average length of a life of a person? You could think of seconds in a day, hours, etc. doing the conversions. It turns out to be roughly 2 billion seconds. The weight of a paper clip. Weight is always challenging. It is roughly a gram. One kilogram is 2.2 pounds. A challenging one. The size of a cell. Male Student: Nanometers. Professor: That is ten to the - 9. A little off. It is more like 10 micrometers. I want to do an example. I think recycling is important because we have limited resources in the world. I want to estimate how many aluminum cans are used by the United States in one year. Think about that. You can chat with the person next to you. [Students working.] Does anybody have an answer? Male Student: 15.6 billion. Professor: Pretty good answer. Any other answers? How would we do this? Male Student: Ten a week for each person and 52 weeks a year with 302 million people in the US. Professor: Exactly right. We want to estimate the population of the US. Roughly 300 million people. I think it is more like 350 million, but 300 million is fine. We have to estimate the number of cans people use. You can think of how many they use in a week and multiply by 52 to get the number of cans in a year. [On board.] Number of cans in a year equals population roughly times weeks in a year times the number of cans that the average person uses in a week. Some people might drink less than ten. Some people might not drink any at all. Maybe I like water, or bottles not cans. If you just need a hand-waving answer,

19 something like 10 billion more or less, that works well. This is a good skill. A funny thing I like to think about is if you thought about recycling each of these. In some states you get 5 cents per can. Let's say you have these cans. If you multiply that by 5 cents, you have millions of dollars. We are talking about all of the cans yearly for the US. If you divide 500 million by the population, it is about two dollars per person per year. Personally, I do recycle, but I don't get the money. Someone else can have the 2 dollars a year. That is estimating. Significant figures. I am not going to test you on sig figs in this class on the test or the homework. I don't care. I want you to be fairly accurate. Within one percent is nice if you have exact numbers. If you use 3 or 4, that is fine. You don't have to have a specific number. Don't worry about them for me. However, other science classes will use them. Your lab may use them. I think that is up to your TA. It is nice to know about them. I did a discussion of saying I was ten feet from the wall. Female Student: Do we take your final? Professor: You will take my final. It s not the same final for another section. If I measured how many feet or meters away I was there would be some error with that. That would be reflected in the signification figures you used. That indicates your confidence in what you measured. If something was 22 inches long, I have two significant figures listed. I am sure it is somewhere between 21 and 23 inches. If I said it was 22.0 inches, I believe I am accurate to within 0.1 inches. I was going to do an example to practice. You can do it if you want to on your own [End of class.]

20 Friday, January 13, 2012 Professor: Let's get started. I wanted to start today by telling you some of the comments you made on the questionnaire. Some of you made comments on the homework. I think the answers illustrate that we can connect on a level. What you want from the class is what I want from the class. If there is a discrepancy, we can talk about it upfront. I was happy to see that most of you are interested in learning in this class what I am going to teach. Let me reemphasize my goals. I want to teach you what physics is about, but also improve your problem solving skills. I also want this class to be stimulating to your curiosity about the world. Many people hope to use the skills learned here in their own fields. That is why physics is required for you: to use analytical skills, even if not exciting to you, in your own fields. We will do a physics movie review in here. You can pick a scene from a movie relevant to your field. A lot of forensics people did reviews of films about things like zombies so they could talk about smashing zombie heads. Some of you expect to see a lot of problem solving in the lecture. I will tell you that that is not the main purpose of the lecture. We will do some in class, but mainly I want to clarify confusing concepts from the reading to give you a basic understanding of these topics. If we have time we will do some problem solving, but the concepts are more important. Also, we don't do problems extensively in class because your book does that. [On overhead.] I can show you an example of a homework problem in the book. This is the eighth edition. You can have either the eighth or ninth editions. [On overhead.] Here you have a problem. The next section is strategy. It tells you how to think about the problem. Then it goes into the math in plenty of steps and you have practice problems. I want to help with what the book is not good at,

21 which are the conceptual ideas. If you are having problems with problem solving and the book along with homework and practice problems don't help, come to my office hours. I have those to help you. Just to emphasize, the purposes of the book are several. First, to provide a background before the lectures. I want you to read before class so you know what we are covering and so you have done practice problems. We can refine that in lecture. It is also a resource for detailed explanations. We only have 50 minutes. That is a long time to you, but if I have to give detailed explanations for things, we will not get through a lot of material. You have all those references in practice problems and solutions. For the text, both the eighth and ninth editions are fine, as well as the e-book. I also asked how much time you think you have to spend on this class. I am counting lectures, lab, time spent on homework and then studying other things. This is a lot of time. You will need at least ten hours a week to give this class a good shot and likely get an A. Some people are hot shots who can do it faster, but be realistic. It does take about ten hours a week. The class is not simple problem solving. You have probably not done this a lot. A lot of classes require memorization. I don't do that. I give you conversions and equations on exams. You have to know how to apply them to the problems. Any questions about the questionnaire in the homework or my thoughts? OK. Last time we talked about the importance of units. We did some examples of unit conversion. If you are struggling, practice quite a bit. If that doesn't do it, come see me in my office hours, as with any topic. Converting units is something we will use over and over again no matter the chapter. Estimation is a useful skill we will use some in this class. We estimated the number of soda cans used in the United States in one year. We also briefly talked about significant figures.

22 There are more lecture slides than we got to last time. I am not that worried about signification figures. If you are, do practice problems. Lab will go over it more. On Web Assign, the answers are not at all graded on significant figures, but use more than one. Three is a good number. One or two can cause rounding issues. I generally advise you use at least three. The first homework is due tonight, a minute before midnight. Most of you know this. Last I checked, 151 out of about 180 people in this class were on Web Assign. The median score so far is 21.4 out of 20. Most of you are already getting extra credit. I encourage you to do that. If you have not, do it earlier next time to take advantage of that extra credit, too. While we will use the I-clicker some today, but it is not graded. Who has them today? Lots of people. Great. We are using them today, but the use is not graded today. I want you to practice some. It is OK if you don't have it. You can register after using them once in the class. We will start using them on Wednesday so make sure you have them. Today we will talk about motion in one dimension. We will define displacement, velocity, speed, and acceleration. We will also address common concerns. A lot of people get confused about the difference between instantaneous acceleration and average acceleration and the difference between speed and acceleration. [On overhead.] I will start with an observation. Have you noticed that when driving down the highway, it frequently seems there are more cars going the other way on the interstate than the way you are going? Have you observed that? Some? You think you are just lucky? Why might it seem that way? Maybe you are lucky. Everybody else is going the other way and you have a free highway. Female Student: You can't see people behind you. Professor: You can use your rear view mirrors and look ahead. Why else might it seem why there are a lot of people going the other way? I will try to relate this to what you have read. We are talking about the frame of reference. On the highway, you are in the reference frame of your vehicle. If a person is going 70 miles per hour, they may

23 look like they are going faster. You can drive past people. You can wave or do any gesture you want and keep going. The people are going the other way at 70 miles per hour while you are going the other direction at 60 miles per hour so you have to add those. You have 70 that way and 60 this way. [Gestures.] That is 130 miles per hour. These people appear to be going by you faster than the people going in your own direction, so you can easily see a bunch of them go by. This is frame of reference. Generally when talking about speed or something, we have to have a frame of reference. We have one car that is moving at 55 kilometers per hour. I will use kilometers per hour to get you used to metric terms. The other is going 65 kilometers per hour. In the ground frame, if you were standing on the road or a patrol car, you would see one at 55 kilometers per hour and one at 65 kilometers per hour. In the reference of the car on the left, the car on the right is only going 10 kilometers faster. It doesn't matter the frame of reference you use. The concepts of physics still apply. We will generally assume the reference frame of the ground. Keep in mind that you could switch to another frame of reference, like a person on a train who wants to throw something off of it. You always have to define it. A frame of reference is represented by a coordinate system. You have an x direction. It is positive in some direction. [On overhead.] Here it is to the right. Am I going in a y direction? No because I am not jumping up and down. Is there anything that says I can't call this the positive x direction? No, I could. The answers from physics would be consistent with that, but what might happen is that I have a positive velocity in this direction. But if that was positive x, I would be moving in the negative direction x with a negative velocity. If we calculated the time it took me to move from one direction to the other, it would be the same. Keep track of signs. They can make a difference. You can have a problem. We will see examples of that.

24 The directions of the arrows are important for setting up equations for problem solving. [On overhead.] If you don't write this down as you do problems, you will get confused easily. Female Student: If you are doing negative x in one side, do you have to change the y? Professor: No. They just have to be 90 degree angles or you will have to do a lot of trig. Keep that nice 90 degree angle between the two. Displacement is the first thing I will define as far as motion. It is the change in position of an object. If I stand in this spot initially and walk over here, I have changed by position. I have been displaced. I will do an example. Let's say you have a car that was originally parked 3 meters to the right of the house. I use meters so you are using the metric system. The driver goes to get gas, groceries and maybe sees a movie. This time he has to park 5 meters to the left of the house. He is displaced from where he originally was. We have to have a frame of reference for the problem. I will pick one that is centered in the door of the house. That is my choice. [On overhead.] We could choose something else and get the same answer as we will see. My initial position is at positive 3 meters to the right of the house. My final position is -5 meters. It is in the negative x direction. Displacement is the change in position of an object. Anytime we find the change of a variable, we will take the final position of the variable minus the initial. We have the final position minus the initial position. Let's plug in the numbers we found. We have a final position of -5 meters minus our original position of 3 meters. This seems simple, but we start here to get to more complicated things later. Now let's show a vector. Displacement is not only about the distance between two points, but it also represents a direction. We have a vector from the initial position that points to our final. We have a vector of about 8 meters and the

25 direction it points at. It is 8 meters in the negative x direction. In Chapter 3 with motion in two dimensions, we will have x and y components. For now, the vector suggests if it is positive or negative for x. In one dimension, it is simpler. You can do it in two or three dimensions, or even multi-dimensions in higher physics. What if we did a different frame of reference? It didn't have to be at the house. It was just convenient because we talked about where the car was in relation to the house. I could pick a point on the car. Capital Y and Y' (Y prime) refer to that. My new initial position would be zero. I am taking the reference frame of the car. My final position is -8 meters. The distance didn't change. We have the same difference between the positions. We have the same vector that has not changed either. [On overhead.] Now we have the first clicker question. This will not be graded. For those of you with clickers, make sure they are turned on. You probably see something like AA in your screens. Do all of yours say ready when turned on? It is OK if it doesn't. Give me a second. You can now answer the question. You can change your answer if you desire. I will have your last answer in my results. I am getting several answers. We have a bicyclist going around a triangle. We are finding the magnitude of her net displacement after her trip. I have about forty answers so far. It is OK to guess if you don't know, particularly today because it is not graded. Female Student: How do you know if it synched? Professor: Let me double check. I have 67 answers so far. Does anyone want more time? I am going to look at these results for myself and then I will decide if I want you to see them. Sometimes I decide to go on because you have it. Sometimes it is a fun answer. For illustration, I will show you this

26 time. What do you think the right answer was? [On overhead.] E. Let's remind ourselves what the right answer was. I should be able to select it. I am getting used to this just like you guys are. Don't change the answer on me. That is not cool. [Class laughing.] E is the right answer. [On overhead.] Let's go back to our thing. E was zero. Most of you got it. The net displacement is zero because the biker returned to the initial position. The net displacement didn't change. They traveled a distance, got some exercise, but distance is not displacement. [On overhead.] A couple of things to emphasize. The sign of displacement indicates a direction. Displacement is a vector. It has direction and magnitude. We will get to those more in Chapter 3. Think about what a vector is now and what isn't. Distance is not a vector. It is a scalar. It just has a magnitude associated with it. If we asked the distance the biker traveled, you could add up the sides of the triangle. That is an easy problem. Any questions? Let's do an example. I want you to think about doing this problem on your own and then talk to the people around you. Some of you will find this problem to be easy and others will not. That is absolutely fine. We want you on the same page. If this is simple to you, work with the people around you to make sure they get it. [On overhead.] We are talking about a train's motion. I will give you a few moments to do this. What do you think the 40 is called? I hear some velocities. Any other thoughts? Velocity is not the right answer, but it is close. Speed. What do you think the difference between velocity and speed is? Velocity has direction; it is a vector. Speed is just a magnitude. When I am driving down the highway and the cop car is sitting here, he doesn't care if I am going 79 miles per hour this way or that. I am still speeding. Speed is the magnitude. Velocity