Beautiful Physics: A Summer Mini-Course

ESU, the Enrichment Studies Unit, is a really neat program here at Queen's. Instructors (usually grad students) can submit a proposal to teach a mini enrichment course on pretty much any topic they are passionate about. A diverse range of proposals are chosen, and the instructors set out to design engaging curriculum on their favourite topics. I think it's an ideal way to run these courses - giving autonomy to instructors to teach what they love.

So naturally, I wrote a course on... the history of penguins. I'm kidding, of 'course'.  My course was called "Beautiful Physics: Light and Sound".  I took a very different approach to the teaching style I used this past year in tutorials.  My whiteboards only came out twice - first for a boggle-style competition brainstorming all the different types of waves we knew, and later for a pictionary review game - we didn't do any problem solving because the students' math skills were too much of a barrier.

Instead, I went for a purely conceptual course with the goal of inspiring questions and finding a couple answers. One thing that I found interesting and encouraging: even without math, the course remained challenging for the students - this was important to me since it was an enrichment course for keen students. (Though a custodian saw the play-doh we used for stop motion, and refused to believe that I wasn't teaching kindergarten students - I was mildly taken aback. I still like play-doh... )

So we did a waves a hundred ways. The human longitudinal wave was a fun one, since it involved knocking over your friends. Similarly, the refracted human wave - lines of students walking quickly on pavement (representing light in air) and slowing down when their feet touched grass (representing glass) worked well for creating an experience of refraction.

We applied refraction to water waves, asking non-intuitive questions like:

As you can probably tell, the "lectures" were mostly done using Peer Instruction. It's easy to do and is the most popularly adopted strategy coming out of physics education research. So at this point - as a 'reader' in my class, you get to pull out your A B C D flashcard and vote for the most likely explanation you can think of for why water waves always move towards the shore. Then, find a friend, discuss the question with them, and then return to reading.

Wait - did you really discuss with a friend? Hmm, I think you should share the best explanation you can come up with - and see if you can tie it to refraction - in the comments. Next week, I'll tell you the rest of the story ;)

We went on to learn about refraction of different frequencies, chromatic aberration, and of course the question:

We looked at dispersion of both light and sound. We did sound dispersion with one of my favourite simple demos - try hitting the end of a metal slinky while holding the other end up to your ear. It's Star Wars! Not kidding! Buy a metal slinky right now and try it. Yes, right now. What happens is this: a clap or tap is made of a thousand different frequencies (or pitches) - high ones, medium ones, low ones, etc. But high frequencies travel faster in metal than low frequencies, so the high ones make it down the slinky and to your ear first... then the medium ones... then the low ones. So you hear Star Wars!

The other place we looked at dispersion was in optical fibers. We learned that in multimode fibers, light that bounces around (by total internal reflection) a lot in the fiber has to travel further to get from Kingston to Columbus than light that goes basically down the middle of the fiber without too much bouncing. The light that travels further takes longer to arrive; therefore the pulse smears out in time:

That's a real problem because then the skype conversation can't be interpretted by the computer in Columbus, and the conversation would fail! So what would you do to fix the dispersion problem in optical fibers?

Once again, discuss, drop me a question or two, and let me know what you think would work to reduce pulse dispersion in the comments! I'll explain the solution next week :)

So as you can tell, we did a lot of waves. Here's a sense of the topics we covered and questions we asked. If you're teaching anything related to these areas, feel free to drop me a note and we can share lesson plans!

• Moire patterns  - why should you not to wear a striped shirt on TV?
• Thin film interference - why do you see rainbows on puddles of gasoline?
• Doppler effect - how do we know that the universe is expanding, and why does the pitch of a motorcycle engine changes as it drives past you?
• Reflection - why do you look upsidedown in a spoon?
• Virtual images - how to make pigs fly (or look like they are)
• Total internal reflection - how does data travel to talk to a fabulous Jeremy via skype, or how do you trap a laser beam in a bending stream of water?
• Polarization - how do 3D movies work?
• Resonance - what do the Tacoma bridge (see this clip: http://www.youtube.com/watch?v=3mclp9QmCGs), a flute,  a swing,  a guitar, a singing bowl,  and a washing machine have in common?
• Overtones - how do you force nodes on a guitar string?
• Quantum, Relativity and other fun topics that students requested we learn about

Whew! That explains why I slept for 12 hours on Thursday night! So as you can guess, I was worried they would forget everything as soon as they'd learned it. I decided that I wanted the students to at least remember one thing, and gain a general sense that physics is the coolest subject ever. So the students made stop motion movies in groups to teach one concept to their friends. 

This group made a video about how a rainbow is formed. I was pretty impressed with the quality of the physics they explained in their video! http://www.youtube.com/watch?v=OR0SOlJ_9d0. Other groups had more trouble explaining the physics, but did have a lot of fun making their video - which was half of the goal. This group went for a Harry Potter style Schrodinger's cat video. http://www.youtube.com/watch?v=f1VBMc_8kkI&feature=youtu.be. And this group did a creative mix of a Schrodinger's cat and the Doppler Effect to tell a story of resuscitating the poor cat after he was observed to be in the 'dead' state. http://www.youtube.com/watch?v=8H-Qa5cbLXM&feature=youtu.be. It was a bit of a tricky call for me to decide if their choice of music for the credits fit the requirements of PG only. I decided this was a battle I wouldn't pick.

There were other battles I did pick. We had some sad issues with emotional and verbal bullying in the class. But I decided to take a different approach than the traditional scary "stop the bullying" approach because I know they've all heard that talk before.... and the bullying obviously hasn't stopped. So I chatted with the class about my experiences with bullying. The fact that empathy and interpersonal skills end up being way more important than putting people down to get ahead. That it's actually a good thing to be a bit quirky and have a personality that stands out when you're looking for a job. That it means a lot to have learned that you can persevere even when life is tough.  I think it helped that by the time we had the chat on bullying, they (including the bullies) liked me enough as a teacher, and were quite surprised to hear I was just like the kids who they were excluding and calling names.  

One of my goals in teaching the course was to show my students that physics goes way beyond our stereotypes as a subject that's simply about trains, airplanes and blowing things up.  It's a creative and beautiful subject that needs all kinds of people - men and women, introverts and extraverts, silly and serious, etc.  I hope the students took that message home. But I hope they took more than physics home. I hope they learned a bit about treating each other well too.

10 Strategies for Physics Teaching Assistants

My supervisor recently asked me to put together a "top ten" list of practical strategies for physics teaching assistants. Of course with only my first year of TAing under my belt, I am clearly not the most experienced person for the job, so I based this content in loads of physics education literature written by people far smarter than me.  I would also love feedback from you - friends who have taught physics, learned physics, or have simply experienced teaching or learning of any subject before. What resonates with your experiences? What sounds flowery and unrealistic? 


Teaching physics is not a trivial task. Even Richard Feynman, famous for his lectures, had a student remark,

"In advanced lecture courses, [Feynman] was inspiring, but... an hour later, you'd wonder what you learned.'' 

Every physicist, who wants to successfully inspire and communicate physics to the next generation, encounters challenges in teaching. Our elegant explanations are useless if our students can't construct their own understanding of the concept. But facilitating this kind of lasting learning is no easy task.

Fortunately, just as we've learned physics by practicing and studying physics, we can also learn to be great physics teachers by practicing and studying teaching. The following are ten strategies you can use as a successful physics teaching assistant. Some may seem obvious to you. That's great! Other things may surprise you - do question them! I encourage you to learn about the areas that surprise you, try strategies out in your teaching, measure the results, and discuss your experiences with your colleagues and with me.

1. Address prior knowledge

Students need to build knowledge into a hierarchical structure and organized mental framework. Your students have a whole host of ideas about the physical world, constructed through their experiences so far. If you simply tell the students new information without addressing their prior knowledge, they will fit your lesson into a perhaps incorrect framework, rather than adopting the framework you want them to learn.

• Don't merely ask a student, ``Did that make sense?'' Ask the student a conceptual question to make sure they understand. Borrow ConcepTests from Dr. Eric Mazur's Peer Instruction to get a few ideas of good conceptual questions.
• A misconception was likely developed through an experience in the physical world. So create a new experience to directly addresses the misconception. Set up the thought experiment or demo. Ask the student to predict what they expect will happen (and listen for how the student is thinking about the situation). Perform the experiment and observe what happens. Have the student explain ``why'', listening for understanding, not just right answers.
• Ask the professor of your course if you can administer a test of conceptual understanding such as the Force Concept Inventory. This will allow both you and the professor to obtain a sense of what your students know at the beginning of the semester.

2. Inspire intrinsic motivations

Your students do want to learn. Yes, even the life science majors who "have" to take physics. We all have intrinsic motivations to learn about our world - your challenge as a teacher is to inspire those motivations. Raise questions in your students. Don't just give them answers. Bring students onside so that they are not merely tolerant participants in your active classroom, but are actively engaged with physics.

• Have fun! Use problems on topics which make your students smile. (Perhaps an Angry Birds conservation of momentum problem)
• Tell students why you're asking them to do an activity. Appeal to their desire to learn. (eg. We're going to act out a circuit using ourselves as electrons and gummy bears as voltage because having a concrete image of current and voltage will help us remember and understand these ideas... and because we like gummy bears.)
• Use challenging problems which encourage students say, "Hmm, I wonder if..."
• Don't frequently remind the students, "This will be on the exam". This statement takes attention away from the students' internal desire to learn. Of course it will be on the exam - you don't need to remind them.

3. Care about marks

We've all made the frustrated complaint, "My students don't care about learning physics. All they want is a good mark". Of course our goal is to help all our students learn physics - and hopefully we've successfully inspired our students' intrinsic motivations to learn physics too. But they also care about marks for their medical school applications, for keeping scholarships, etc. And if something matters to a student, it matters to you - because your students matter to you.

• Make sure there exists a course outline ready for the students for the first day. You don't need to read this to your students during the precious tutorial time you have. But you do need to make sure that all students have access to it online or in hardcopy.
• Give students a rubric which details your expectations of the assignments or exam questions you will be marking. Stick to the rubric when you mark.
• You should rarely see surprised looks on students' faces when you return an assignment or test. This can be a check for you to determine the clarity of your rubric.
• If you get to decide how some marks are allocated, use marks to communicate what you want the students to value: Do you value conceptual understanding? Then be sure to have more than just quantitative problems on your assessments. Do you value innovative design? Then incorporate elements of design into the lab rather than doing purely cookbook labs.
• Don't speak dismissively when your students tell you their concerns with grades. Listen, empathize, and set clear expectations - marks are not given by you, but earned by the student.

4. Hold high expectations for your students

Lecturing sets the lowest expectations for students; it assumes that they can do no more than passively copy down the set of symbols you write on the board. We have top students here\textemdash expect these students to engage, think, and learn in your class\textemdash and structure your class accordingly. Your role is not merely to provide information; you empower your students to see that they have something worthwhile which they can contribute to the classroom. When you set high achievable expectations for your students' learning and help your students meet these expectations, your students' physics self-efficacy (students' confidence in their ability to do physics) will improve. Self-efficacy is associated with both increased academic success and retention in a physics major.

• Tell your students that you want everyone to achieve an A. Or better yet, show them with the effort you put into teaching them. 
• Use engaging strategies such as Peer Instruction in your tutorial - create a classroom culture where students know they are expected to wrestle with new concepts in class.
• When a group gets stuck while working on a problem, don't jump in and simply provide the solution. Ask leading questions which give the students an 'in' to start working on the problem themselves.
• As TAs, we are rarely the best teachers in the room. Encourage students who have just made a breakthrough in understanding to teach their classmates.

5. Pay attention to how you talk about your students

Value and respect your students in your discussions with colleagues. As you speak optimistically about your students, you may find your own perspective changing - you'll notice more of the potential in your students. Also, you are an essential aspect of building a great teaching culture in our department. When you value your students in your conversations, your colleagues may see more value in their students as well.

• Talk about your students' learning more than you talk about yourself teaching. This will take the focus of your discussion with colleagues away from elegant derivations, and put the focus on how you can better help your students learn.
• Focus on the success stories. Share the excitement of a struggling student making a breakthough in understanding.
• When a student is driving you crazy, find at least one good thing to say about them rather than complaining about them to a colleague.

6. Prepare for class

It's no surprise: to teach well, you need to prepare both your content and creative strategies for communicating this content. Don't waste the students' time (and yours!) by floundering, providing vague explanations that serve no purpose except to cover up a lack of preparation, or directing the students along unhelpful paths.

• Solve all the tutorial problems yourself before teaching them - don't just read the solutions before class.
• Talk about the material you plan to teach with friends or family who aren't in physics. What kinds of questions come up? Practice answering these questions.
• Don't underestimate the ability of your own brain to forget. Sure, you may be teaching "easy first year physics material" but that doesn't mean that every concept (and especially methods for teaching every concept) is at the forefront of your mind right now. A good teacher continues to put effort into preparing for class and improving their teaching no matter how many years they've taught the course.
• When students ask a question that you don't know the answer to, don't give them a vague answer to hide the fact that you aren't sure. Be honest, and if possible, look up the answer after class or ask the student to do so and share what you learn with the students the following week.

7. Teach your students how to learn physics

The only people in your classroom who can do the learning are your students themselves. When we try to simply make our students download information from the blackboard, we miss the crucial question of how learning happens. Get students thinking about how they are learning and how they could learn more.

• When a student gets stuck on a problem, ask him or her "How are you approaching this problem so far?"
• Recognize the diversity of learning styles in your class. What works for one student might not work for the next student - this is the fun and challenge of teaching! Just as you use multiple teaching strategies to communicate information, encourage your students to try different ways of learning and studying until they find a technique that works for them.
• Model how you think about a problem, not just how you would set up or solve the problem. Remember that you're not trying to teach your students how to solve the "sliding block on ramp" problem - you're teaching your students how to think about physics so that they can solve new problems, eventually solving problems that we don't know the answer to.
• Encourage students to write a brief summary of what they learned at the end of each week - both concepts and skills.
• Ask your students to tell you what they're doing well (e.g., I'm starting to pause and lay out the concepts before diving into formulae at the start of a problem now) and what they need to work on (e.g., I give up too soon when I don't see a clear path to a solution). For efficiency, this could be coupled with obtaining feedback for your teaching - at the end of tutorial ask your students to write advice for your teaching on one side of the page and advice for their own learning on the other side.
• Have your students teach each other, but tell them that they can teach only the overall concepts they used in their solutions - they can't get stuck in the mathematical steps they followed.

8. Build positive relationships with your students

Good communication in teaching is not just about delivering good content. Building a positive rapport and relationship with your students genuinely improves their motivation to learn in your class, and results in greater academic success for your students. It also just makes teaching so much more fun.

• Make sure you are finished setting things up for your tutorial or lab 10 minutes early. Then spend the 10 minutes before class just chatting one-on-one with the students who are early.
• Smile to your students.
• Use your sense of humour in class (of course being mindful to respect the diversity of the students in your class).
• Learn and use your students' names. To make this easier, ask for a copy of the students' names and faces. The professor of the course probably has a page of names and faces that you can photocopy and post at your desk.
• Use your personal hobbies. For example, if you like baking, consider bringing a snack for your students on occasion. Or if you have a keen class, ask the students to sign up to bring food to tutorial. 
• Find out what hobbies your students participate in. Then slightly change the tutorial problems so that your students are the star of a problem. (e.g., Instead of "a car accelerates..." change the problem to say "Jason accelerates on his skateboard...")

9. Create an environment that makes learning happen

You may not have access to expensive teaching technologies in your classroom, but fortunately, engaging teaching is a much more important factor in improving student learning than having a fancy classroom. You can make the environment you're given a successful teaching space. Also, classroom environment is not only created through physical items in the classroom. The way you communicate with the students is the most significant aspect of creating a positive environment.

• If you have a poor classroom and if it's a warm sunny day, bring your class down to the lake and teach in the friendlier environment of the outdoors, if this fits with the activities you have planned.
• Buy white boards (approximately 20$ for a sheet which can be cut into eight 2ft x 2ft white boards) for the students to work on problems in groups. This is particularly helpful if you hope to take some classes outside or if you lack desks in your classroom.
• Create an environment where students feel safe making mistakes. When a student gets confused while solving a problem, say "Let's go back to what you know". Don't pretend that they're doing fine, but don't emphasize their mistake either. Bring them back to a point in the problem where they feel comfortable, and ask leading questions (that they do know the answers to) to send them down the right track.

10. Obtain and use feedback continually

You may have heard the quote, "You haven't taught until they have learnt", which is attributed to John Wooden. Your students are a highly valuable resource to you. Continually check if your students have learned the material you thought you were teaching. Change your teaching accordingly.

• Give all your students a piece of paper at the start or end of your class. Ask them to tell you one concept that recently became clear (and how it became clear) as well as one concept that they would like you to cover again. Or ask them to tell you what helps them learn and what is hindering their learning in your tutorial.
• This takes courage, but it can be very helpful: Ask a professor or fellow TA to observe one of your classes and give you feedback. Often an observer at the back of the room can identify whether or not students are engaging with the material better than you can.
• Class discussion can be useful for checking students' understanding only in tiny classes (ten students or fewer). In medium to large classes, use another strategy such as Peer Instruction to check for understanding. Class discussion in medium sized classes causes many students to disengage and listen passively.
• Attendance can be one mode of feedback from students. If the students feel that the time they spend in tutorial is useful for their learning, they will likely come to the tutorial. If they aren't learning in your tutorial, they will likely not attend (unless marks are attached to attendance).
• It is helpful to measure the effectiveness of your teaching with a standard instrument such as the Force Concept Inventory, which you can administer in your tutorial at the start and end of the term. Gains of 40% - 70% on the FCI will indicate that you're on par with interactive physics courses in North America.

Great TAs are always learning to become better TAs. Keep learning new strategies for teaching, trying them out, reflecting on the feedback you obtain, and improving your teaching. And of course teach me when you come across something that works well for your class. All the best!

Faith vs Physics?

It's a question that I've asked myself many times, and a question that's been asked of me:

How can you be a christian and a physicist at the same time?

This is an important question to me. I'd rather not hold conflicting identities - if these are indeed conflicting identities. And in fact, the most common answer I've heard from both parties - non-christian physicists and non-physicist christians - is: 

You can't.  

Some Physicists have told me that since faith requires looking at the world in a different way than science looks at the world, faith must therefore be 'wrong' by a scientific definition. But it seems downright silly to start with the assumption that the scientific method must by definition be the only ruler by which to measure faith. We're a post-modern society; we've moved beyond these sorts of limited circular definitions.


Others have said that physics somehow replaces God. Now the Higgs boson may hold the common name of 'God particle', but it really doesn't follow that we've somehow replaced God simply by learning more about the incredible universe we find ourselves in. I certainly can't see any reason for Christians to be afraid of physics - it's done nothing to disprove or replace God (though the media and some physicists have been known to put a controversial spin on physics research to boost readership). I don't believe learning about creation nullifies a creator. 


Some Christians have told me that physics is like Babylon, and goes against faith. Physicists are trying to play God, interfering where we shouldn't interfere. Hiroshima is sometimes used as evidence for the 'dark side' of physics. But while physics has led to the creation of some harmful technologies - I certainly don't want to downplay complex tragedies like Hiroshima, it has also given us an amazing array of technologies which improve our quality of life, save people from otherwise impossible circumstances, let us experience the phenomenal beauty of our world (and beyond!), and connect us with each other. Also, physics describes sunshine and rainbows - and who doesn't love that? If God made us as creative curious people, it seems only natural and good that we would want to invent and learn about the universe we live in. 


But 'You can't' isn't the only unsatisfying answer I've heard. Other's have told me:

You can... because physics explains faith.

But does it really? I'm sure we've all seen the books and websites that stretch and misinterpret dear Mr. Schrodinger's and Mr. Heisenberg's equations until they barely resemble the beautiful physics they were supposed to describe. And after this sad process, these stretched concepts are used to say that we can scientifically 'prove' God's existence. It hurts my physics heart to see the concepts I've studied and fallen in love with not only distorted beyond recognition, but also taught poorly to innocent people who are just starting to learn about our field.

So I'm still in the process of answering this question - can faith and physics be friends? And perhaps I will be for some time. But for now, my current answer is:

You absolutely can be both a christian and a physicist - because neither of these identities requires the other to be wrong. 

I believe that the bible was written so that we can know God, learn how to love each other and love God, learn how to lead lives that honour God, and other such good things. I don't believe it was written as a science textbook. So I don't need to warp physics to awkwardly force it to fit with my faith.  Similarly, my physics textbooks were not written for the purpose of teaching me about God's character. So I don't need to change my faith to fit with my quantum class.  

The passage that most people cite as the main source of tension between physics and christianity is Genesis. I think it is very helpful to think about the role and purpose of the creation story in our faith. If we believe that the bible was written for the purpose of being the first science textbook, we might assume that the creation story was written to provide a scientific record for us to go back and analyze the age of the earth. If this really is the purpose of the bible, then it would be pretty much impossible to be a christian and physicist. But this seems to be a very unlikely theory: that God would send his Son to live with us on earth, build relationships with us, and write the story of the bible - all for the purpose of giving us a science textbook? And if the bible was written for the purpose of teaching us science, I'd have to say, it doesn't do a very good job at accomplishing this - where are the pretty colour coded diagrams?

Instead, if we believe that the bible was written to reveal God's character and give us the opportunity to know God, we will read the creation story very differently. We'll read the incredible truth that we were made in the image of God, called to be stewards responsible for caring for His world, called to love and care for each other. As people made in the image of God and stewards of our world, we can absolutely be creative and innovative physicists, finding solutions to climate change and environmentally safe sources of energy.

The bible does a great job of telling us the story of God's love and faithfulness to His creation, and explaining how we can live in relationship with God and each other. Jackson's Classical Electrodynamics does a great (well, at least okay) job of explaining Maxwell's equations. So I believe we can respect and embrace both faith and physics without denying either.  Probably the best way to do this is to learn about both :)

Special Relativity: Starring Trains

Back by popular demand... another physicsy post! Well, the truth be told, the only person who requested another physics post was... well, me. But this post is exciting because it stars the classic subject of many a dear first year physics problem: trains! Yay trains :)

Let's say that you're a train, and you're having a really nice time with your tank engine friend, Thomas. You might think to yourself, I'd like to have more time with Thomas. And as a train, you've likely heard of special relativity, so you turn to Einstein to ask how to stretch out time.

Einstein will likely tell you to get moving. In fact, he'll say you should move so fast you're almost travelling at the speed of light. Why is this? Well, let's start with a seemingly unrelated experiment, and then we'll see what this means for you spending more time with Thomas.

The build up:
Muons are little particles who don't live very long. We can study muons in the lab and find that they only live for around 2.2 microseconds. So even if muons were travelling even as fast as light, they couldn't possibly travel further than 600 m before they die. But... muons are produced in the upper atmosphere (10 000m up), and some are still able to make it all the way to the earth's surface! How is this possible?

Einstein predicted incredible experiments like this one (even before anyone had tried it!) with his theory of special relativity. One of the things I love about special relativity is it's simple basis - just two postulates:

1.  Any reference frame (aka. perspective) is a good one as long as it's not an accelerating reference frame. Physics works on a moving train. Physics also works on the train station platform. To clarify this point: imagine you are in outerspace (you're a space-train perhaps). If you see another space-train getting closer, you can't tell if you're moving towards it or if it's moving towards you. And Einstein's point here is that it doesn't matter - both of you have equally valid reference frames. 

2. The speed of light is constant no matter what reference frame you observe it from. In our example above, the other space-train moved at a perhaps 120 km/h in your reference frame, but moved at 0 km/h in its own reference frame. Light isn't like a train: in every good reference frame, it travels 3x10^8 m/s (in a vacuum). 

A classic way of understanding some of the impacts of these two postulates is through the thought-experiement of a "light clock".  The clock in my grandma's living room ticks every time a pendulum completes a swing back and forth. This light clock we've imagined ticks every time a pulse of light travels from a bottom laser to a top mirror, bounces off the mirror and hits a receiver on the bottom.


Reference Frame A: Clock is not moving relative to you:
If you are standing beside the clock (not moving relative to the clock), then you observe the light pulse to travel straight up and down. Here's a quick sketch of the situation when you are in the same reference frame as the clock:

Let's do a quick calculation to see how long a "tick" is on this clock. To make the math easier, we'll pretend light travels pretty slow - say 1 m/s. And the height of the clock is 1m. So it takes 1s for the pulse to travel to the mirror and another second to get back down: a tick happens every 2 seconds.

Reference Frame B: Clock is moving relative to you:
Now let's say this clock is stuck to the side of a moving train, and you're standing on the platform watching the clock move past. Now, from your perspective, the pulse will appear to travel on an angled further distance to the mirror, as sketched here:

The key is that it's not some illusion you're seeing. Einstein's first postulate tells you that your reference frame is equally valid. So in this reference frame, you'll see the pulse travel further (say 1.5m to the mirror and another 1.5m down), so you calculate the time for light to go from the laser to the receiver (pretending that light travels 1 m/s) will be 3 seconds.

Wait! What is going on? When we looked at the clock from Reference Frame A, we observed it ticking every 2 seconds, but when we looked at the same clock from Reference Frame B, it ticked every 3 seconds! 


What we just happened upon is the first exciting consequence of Einstein's two postulates: time is relative! It ticks slower or faster depending on your perspective. But then, every five year old already knows that - when you are waiting for an ice cream cone, time ticks so slowly, but when you're eating the ice cream, time speeds up and the ice cream disappears so so fast. Okay, so that's not exactly special relativity. Trains make a more accurate example: From the perspective of a person who is standing "still" on a platform (we know now from postulate #1 that "still" is a very arbitrary word), the events on a nearby moving train are happening more slowly than the events happening on the "still" train station platform. 


So, if you want to have more time with Thomas the tank engine, you should drive your train as fast as you can... right?

The let down:
Unfortunately, succeeding in stretching out time hasn't actually given you what you'd hoped for. When time dilates, every clock - your heart beat, the pace of your conversation, even the rate at which you age - all these things "tick" in step with the new time. So unfortunately, from your perspective, it doesn't feel like you have any extra time with Thomas after all.

However, when you're chatting with Henry the green engine later on, he'll tell you that he thinks you spent quite a lot of time with Thomas. From the perspective of Henry, who is not moving inside his tunnel, he sees you and Thomas moving quite quickly, so he sees time tick slower for you. And he's rather green with envy.

The rest:
Time isn't the only thing that's relative! As we saw from our muon experiment, distance is also relative. As you can guess, the relativity of distance is very related to the relativity of time. And mass is relative too. Mass is a big deal right now with all the higgs celebrations. But for now, I'll pause this post to ask the most important next question: does the higgs boson like hugs?

Physics Vocabulary

Hi Anneke,
Always a treat to hear from you--always something interesting!
You make a lot of interesting points, I like the one about e/m waves.
The downside of the overlap between everyday and physics vocabulary is that students often have to struggle to learn to use those everyday words in the new and special sense that physics assigns.
Force is a vector
Weight and mass are very different
Angle of reflection is measured from the normal
There are 3 kinds of wave motion
Sound and light are both waves, but very different kinds!
Anyway, you know the list...
I think I'm particularly aware of this issue because there are also words in education that need to be differentiated from everyday language--and education has all those dreadful acronyms!
Hope you are enjoying summer!
Tom

The Language of Physics

"It's all Greek to me", some might say when they glance at a typical first year physics equation sheet. And they'd be right: when our physicists of many centuries ago ran out of Roman symbols (or perhaps when they just wanted prettier symbols), they represented lots of concepts with Greek symbols. For example, here's the equations you'd use to describe the motion of ferris wheel:

Admittedly, it can look rather Greek (though hopefully not bleek). That is, of course, until you start talking about physics. In conversation, physics (especially at the first year level) can be quite accessible. Unlike biology's mitochondria or chemistry's acetylsalicylic acid and other silly words I can't spell, physics tends to use the words of everyday conversation to describe the everyday physical world. For example:

• In physics, your weight is the force of gravity acting on you, but in conversation we might describe an argument as carrying "weight"
• We talk about a leader as having "power"
• Yoda would say, may the "force" be with you
• A kind person has a "magnetic" personality
• We "reflect" on our experiences... especially in teachers college ;)

In some ways, I like this overlap because I think it makes physics less scary - we already know the words (even if we don't yet have a complete understanding of their meaning in physics).  There's a common public perception that physics is a set of equations on a page, having little to do with the "real world". For example, when Eric Mazur spoke here this fall, he told a humorous story of a student who asked him during a test, "Would you like me to answer the way you taught us in class, or the way I normally think about these things?"  The overlap between "physics language" and "everyday language" clearly hasn't been enough to change the perception that physics is separate from real life, but I hope it can be of some help in bridging this gap. I also like this overlap for very practical reasons: my memory barely has room for the words of the everyday English language, so I was quite relieved to find that physics didn't require the huge new vocabulary that comes with a subject like biology.


Sometimes, however, this language overlap leads to misconceptions.  The way we talk about electromagnetic waves - as radio waves, microwaves, infrared, visible light, UV, x-rays, etc in the very different contexts of hearing music in your car, warming food, getting a sunburn, seeing a broken bone - I think this actually hides the pretty physics part: that these are all the same type of wave (electromagnetic waves) simply with different wavelengths. The difference between microwaves and visible light is like the difference between singing low A and singing high C. But our language outside of physics hides pretty connections like this. In a different rather funny example of mismatched physics language, this politician (http://thehill.com/homenews/house/179947-gop-leader-on-jobs-speech-voters-are-sick-of-the-rancor) says he is "focused like a laser"... should we tell him that he's comparing himself to an unfocused slowly diverging beam? 


I find the many contexts of "relativity" to be particularly fun and interesting. In fact, I think our social understanding of relativity can be quite helpful for understanding the physical definition. In physics, we say that quantities we measure like time, mass, length, etc. are relative to the reference frame from which we're viewing the event. Very similarly, in social scenarios, our understanding of an event is relative to our perspective on the event. The concept of relativity can be very helpful for us in understanding why another person, who experiences the same event from a different perspective, might react differently than us. Applying relativity to social scenarios can improve communication and foster better friendships. And understanding relativity socially can help us to understand the concept of relativity in a physics context. 


The concept of relativity can also be very helpful to see our everyday challenges in the light of a bigger picture.  I think we all strive to be the sorts of people who look at situations through the lens (to use another fun physics word) of, "What is really important here?" Probably one of our biggest goals in life is to love people. If we see our everyday challenges relative to these bigger goals, I think all of our lives are just better. 


But just like our politician friend probably should have asked his physics friends for the meaning of "focus" and "laser" in the context where he was speaking, we have to be a bit careful not to apply relativity to places where it doesn't make sense. The speed of light isn't relative; no matter what reference frame you're in when you look at the light, it's always going to be traveling 3 x 10^8  m/s in a vacuum. So we can't simply say "It's all relative" because some things aren't. I often don't know what the 'right answer' is, but I do believe there are some fundamental truths that are constant for everyone. I'm not sure I could be a physicist if I wasn't interested in research that could be generalized beyond myself - things that are true for all of us. 

Optical Fibers

One of the great things about graduate studies is the many hats we get to wear.  I've mostly written about my experiences teaching and researching education this year, but I've also had the opportunity to be a student.  I think it is a very helpful thing to be on both sides of the desk at the same time.  

This semester, I enrolled in a quantitative research methods over in the Education Faculty and an electrodynamics course here in physics.  The courses couldn't have been more different from each other, and I'd say I quite enjoyed both courses for different reasons.  Last year when I was in teacher's college, I blogged a bit about how much I missed a really challenging physics problem (this post: http://birefringencemms.blogspot.ca/2011/01/reminiscing.html).  Education classes can sometimes feel a bit like chocolate - they're sweet, fun, and can be very well taught.  But it seems that there's not a great deal of education classes which you could really classify as 'hard' or 'challenging'.  For me, I find that physics classes are more like steak - the content can be a bit dense for me to understand, but you finish the course feeling very satisfied - like you really learned something challenging and interesting.  

My electrodynamics course this semester was exactly what I needed.  Problem sets were typically only 3 or 4 questions, but working out the solution would take sometimes 60 pages.  When you jump through that many algebra manipulations and integrals and you finally arrive at an answer, it can be a real thrill.  There is something just fabulous about stretching your brain for hours, and then suddenly on the horizon, seeing a promising solution like an oasis in the dessert (and hoping it's not a mirage!)  Perhaps this explains why physics can be so addictive? 

The electrodynamics professor taught his course in a fairly traditional manner, but for our final assessment, he kindly agreed to let us do a project instead of an exam! I was so pleased.  The only sad part of this assignment was handing in the essay, completing my presentation, and realizing that I had no one to share all my pretty physics with.  But I have a solution to this sadness!  I am sharing the physics-love with you my dear friends :)  

Therefore, the following is the non-physicsy edition of my essay on optical fibers.  If you enjoy the read, and would like to read the physicsy-edition, just leave a comment for me, and I would love to explain the "why?" behind everything here or even send you my real report if you are interested. 

Optical Fibers: 

You talk to a friend across the ocean over skype with almost no delay in the conversation. Militaries send confidential data around the globe in fractions of a second. You watch a youtube video of a really cute puppy.  You turn on your sweet 90's fiber optic lamp for 'mood lighting'.   How are all these technologies possible?  Optical fibers of course! With the exception of the 90's mood lighting and some other light delivery applications, optical fibers are mostly used to connect our world by allowing almost instantaneous hard-to-intercept sharing of huge amounts of data. Under the ocean, we have many submarine cables which can send data around the world encrypted in pulses of light. Here's a map of where these cables were 5 years ago:

How does light actually travel along these optical fibers? Well, we can get a pretty good sense of what's going on using a ray optics model. Whenever a ray of light hits an interface between two different clear mediums, the light ray changes direction (or refracts). If you hit this interface at the right angle (called the critical angle), the ray will change direction so much that it will end up just travelling right along the fiber. The light is trapped! So our message will stay stuck in the fiber, and will therefore arrive wherever we want to send it. This is called total internal reflection, and here is a sketch of it:

We can use this "ray model" to describe light propagation in big fibers ('big' refering to fibers around 0.0001m in diameter and bigger). An example of a really big optical fiber is a stream of water. Water is not a very practical material for a real optical fiber (especially in the ocean...), but I think it is a rather pretty demo. You can guide a ray of light inside a stream of water using total internal reflection. Here's a picture of this demo in my kitchen:

Kinda looks like the diagram above, eh? A little? To do this at home, you just need a bottle with a hole in the side near the bottom, a laser pointer, some water, and an anneke to ramble on about how beautiful the total internal reflection is.

Unfortunately, if we send data down big fibers we run into all sorts of problems. Pulses of light spread out in time and smear on top of each other so much that by the time they've traveled a long distance (eg. under the ocean), they are completely unintelligible. So instead, we like to make really tiny fibers to get rid of this problem (by tiny, I mean a fiber with a diameter of around 0.00001m and smaller). The trouble is that with a fiber this small, the diameter of the fiber is not much bigger than the wavelength of light, and our ray approximation doesn't work anymore.

What do we do when an approximation lets us down? Do we throw up our hands? No! It's time for us to travel...

Yes Maxwell, not the future. But equally awesome. This is in fact one of the things I find particularly beautiful about physics: its complex simplicity. An incredibly complex system can be described by the smallest fundamental concepts. The fundamentals which describe light propagation are Maxwell's equations. Physics folks like to represent Maxwell's equations like this:

I know this might look a little weird if you're not familiar with the "nabla" symbol (it's actually nothing fancy - just a slope in three spatial directions). But definitely do take a minute to revel in the amazing complex simplicity: those four little unassuming equations just explained every x-ray machine, MRI, computer, light bulb, stove, lightning bolt, sunny day... and the list could go on for literally days of typing! Maxwell's equations describe pretty much anything and everything about electromagnetism. I think this is pretty awesome.

Now you might not feel quite so enthusiastic about these four equations, and this is okay. So for the non-equation-lovers out there, here are Maxwell's equations in words:

i) You can make electricity just by having a changing magnetic field (eg. moving a magnet around).  If you've take a first year physics course, you can connect this to what you've learned: this Maxwell equation leads to a fun little law you might remember by Mr. Faraday.

ii) You can create little magnetic field loops if you have either a current or a changing electric field or both. Take the 'steady-state' case where the electric field isn't changing - what does this give you? Ampere's Law!

iii) Electric charges can be single, or they can find the love of their life and become a dipole (the physics word for happily married couple). If you know where charges are, then you can figure out the electric field they create. This is useful for predicting how the relationship will progress - who will feel forces of attraction? Who won't? 

iv) So far, no one has ever seen a north pole all alone without a south pole companion. Even if a magnet is really big (eg. the earth) and the poles seem far far away from each other, they're always connected by magnetic field lines. It's actually a pretty adorable romance. 

Okay, so now you know all about Maxwell's equations and how pretty they are. But why did we go back to Max in the first place? Remember we wanted to find out how light propagates in a tiny fiber (the kind that they actually use to send data under the ocean).  So next, we do a bunch of mathy cartwheels which combine Maxwell's equations, then we shake things up a bit, and something called the "wave equations" will appear.  Once you've got wave equations, you should be a very happy camper because now all you have to do is solve the wave equations and you can describe exactly how electric and magnetic waves (that's just a fancy way of saying 'light') travel down the fiber.

Unfortunately, when we do our mathy cartwheels, we end up with what's called "coupled wave equations" (quiver in fear). Physically, this means that the electric field wave is influencing the magnetic field wave and vice versa. Practically, this means we have two really beastly equations to solve. We're saved by some approximations though! Most tiny fibers are "weakly guiding" - this means that 'critical angle' we talked about is really small, so the light is pretty much going straight down the fiber. This lets us 'decouple' our wave equations, so we can solve them! When we do this, we get pretty pictures of the electric and magnetic fields. There's a lot of different possibilities (called 'modes') for what you can get - here are two:

This picture is a cross section of the fiber (the dark purple part is the main core where the light mostly travels). And the electric field is represented by the red lines (longer line = stronger electric field). Imagine this as a cross section of a wave which is bopping up and down, while moving directly towards you. Here's another way to draw the second picture: 

In the picture above, I'm representing a strong magnetic field as a bigger height on the 3D graph. The electric field gets small as you go out to the edges, and follows this pretty cosine as you go around the circle. 

That is a snapshot in time of one of the electric field waves, which is travelling down an optical fiber right now to send this blog post to you! There's also a magnetic field wave - I didn't mention him because he's not too hard to find once you know the electric field. He's always just 90 degrees to his buddy, the electric field.  

And that's it - a brief intro to sending data in light pulses inside optical fibers! Now you can dream of total internal reflection and pretty wave patterns the next time you send an email or make an overseas phone call :)  I hope you enjoyed the read!  If you'd like to see the actual math behind light travelling in optical fibers, just leave me a note in the comments and I'd be happy to share!

When I Grow Up - Part 2

I can hardly believe classes are over. I have been so blessed by fifty-two talented and interested students this year. Some moments I'll remember from this year: the amazing weather this spring when we could bring our whiteboards outside and learn physics in the sunshine, the ridiculous errors I made and the comfortable atmosphere we had where we could laugh about them, far too many velociraptor problems, and watching friendships grow between students as they learned together.

The experience certainly convinced me that I would like to make teaching a big part of my career. As described in part 1 of this post, the question of what I want to be when I grow up is mostly answered. So the question of this blog post is: what sort of teacher do I want to be when I grow up? Now I don't have the foggiest idea if I want to be a high school teacher or a prof, a physics teacher or a special education teacher, etc. I do know, however, as every teacher does, that I want to be a great teacher. But when I think of great teachers I've met, they're all so different - so what is it that makes a teacher great?

Well, maybe it starts with not thinking so much about "being a great teacher", but rather focusing on helping my students get where they need to go. As someone who thinks far too much about things, it's easy for me to focus on my teaching rather than on my students' learning. And I think that's an unfortunate place to go - this is how we make teachers who spend hours preparing the most beautiful derivations to write on the black board, but are unaware that their class is actually just having a nap.

Alright, by now you must be thinking - is she actually just going to spend an entire blog post just rephrasing a question without ever really answering it? Yes. That is exactly what I'm doing. The fact is, I just don't know the answer. But...

There are at least some things I am pretty sure of. For example, one of the things I've been researching is what motivates students to go on into second year physics. For my male students, strong conceptual understanding and high grades were highly correlated with choosing a physics major. Makes sense. But for my female students, who have the experience of being a minority in the class, the only two variables I found which correlated with retention were a) their physics self-efficacy (aka confidence in doing physics) and b) the extent to which they felt that the prof and TAs cared about them. This is great because I certainly want to be the sort of teacher who shows my students that I care about them - not just because this could reduce the gender gap, but because I think it is simply a human way to live life. We were created to care about others and to be cared about - it only makes sense for this to happen in the classroom, in discussions about future career plans in the foyer, etc.

Feeling cared about is important to students, particularly the female students in my class, but we can't stop there. Students obviously need the opportunity to build an understanding of the physical world if they're going to be successful in physics. I'm currently really interested in the research suggesting that social environments can be very successful in doing this - that we can build understanding better with others than we can alone. If this is the case, "good teaching" involves less of the traditional download of information through a lecture, and more questions, more stepping back and assisting students as they form new knowledge problem solving together. Practically, this has been a really fun strategy to work on and tweak this year in tutorial.

Alright then, so far we can be fairly comfortable saying that students certainly need to know they are valued and cared about, and they certainly need to learn to do good physics. But this still doesn't seem like a very complete picture of good teaching. I have bigger goals for my students than that they merely be great physicists - I want them to be great people. I want them to care about each other and about the world, and I want them to be inspired to act on that love in selfless, genuine, and thoughtful ways. This is a challenging goal. So let me diverge to look at some examples of this through an analogy to film - I promise that this really will tie back into teaching, so do bear with me.

So I went to see Hunger Games the other day. And I really appreciated the themes the story brought to light. First, the idea of impacting change by acting together: At one point, the main character says, referring to a televised game in which children are forced to kill each other, "What if they all just stopped watching? There would be no Hunger Games." She is of course reminded that this will never happen. Though few people would intentionally kill an innocent child, the public continues to fund these atrocities with their choice of viewing material. The public collectively has the ability to end the games, but no one believes they hold this power - it's the thought process of, "The games will probably occur anyway, so what could be the harm in my watching it?"

The Hunger Games may be set in a post-apocalyptic world, but this theme certainly strikes a chord with our present day. Few pornography viewers would intentionally abuse women, yet every click directly funds this abuse. Few shoppers believe in inhumane working conditions or child labour, but how often do I look into the origin of my new blouse or gadget before I buy it? We could end the porn industry and drastically improve working conditions for employees in other countries. Yet we choose not to, because it's just too tempting to view the small difference our decisions make as being zero difference. (A physics aside: dx may be infinitesimally small, but it's not zero. And in fact when we integrate up all the little dx's we can get something actually quite big.) On top of this, we know these issues are complex, and solutions are not easy to come by. But knowing the complexities involved in finding actual solutions can't simply remove our personal responsibility for our choices to fund abuse.

This brings to mind a second theme in the Hunger Games: the power of the media in inspiring people to act cohesively without necessarily taking thoughtful consideration. At the start of the games, the public is told through video and speeches that the games are a wonderful thing. The children are bringing "honour" to their district, and the games are promoting "peace" by keeping the districts under the rule of the capitol. Of course, many of those directly involved know that this is not true, as evidenced when the father of one of the murdered children sparks a riot. But the crowds, who aren't personally involved, roar with applause at these statements of supposed honour and peace.

A more current example would of course be the Kony 2012 campaign. Many of us saw the emotionally charged video which encouraged us to support Invisible Children in bringing a very horrible man to justice. Watching the video, I think most people would agree that it just felt like such a great campaign - especially from our perspective as people who aren't personally involved. But fortunately, the same technology, which quickly spread the Kony 2012 campaign, also shared with us the responses of Ugandans to the film, such as this one: http://www.youtube.com/watch?v=KLVY5jBnD-E.  In her response, this speaker describes the devaluing consequences of reducing horrific events to a "just catch the bad guy" black and white issue, while intentionally ignoring the complexities of the situation. Facebook postings about Kony 2012 soon came down as we started to consider what our support meant and the impact it had. We asked hard questions such as: "How can we actually go about bringing Kony to justice without many innocent deaths - particularly of the children we hoped to protect?"  Of great importance, we took a tough look at our personal motivations: were we truly concerned and willing to make genuine sacrifices for our fellow human beings? Or in promoting Kony 2012, were we simply boosting our already ridiculous western Saviour complex, at the expense of Ugandans?

I could probably just ramble on all day about these things. But this is a teaching blog after all, and I promised that this does indeed have everything to do with answering the question of what kind of teacher I want to be.  So let's try to get to some semblance of a "point".

I want to teach more than physics. I want to first inspire in my students an understanding that they have the ability to effect enormous change, especially when they act cohesively. But second, I want to teach them to use this very carefully - to think deeply about how the decisions they make effect others, and to act accordingly. We first need to recognize that we can do something about the abuse in the porn industry, the deplorable working conditions in some factories, the atrocities committed against child soldiers, and the many other issues facing our world - we need to realize that our individual choices do make a difference in these situations and can be used for great good. But we also need to recognize that our choices can also be used negatively, and that in acting cohesively without thinking deeply about the complexities in these issues, we can actually make things quite a bit worse. We work through physics problems in tutorial, but I want my students to find thoughtful solutions to the problems that I don't know the answer to. And want them to be inspired to act on these solutions.

The challenge is that I have no idea how to be this sort of teacher. Seriously, no idea. I don't even know if this is entirely the kind of teacher I should be aiming to be - there's likely many important aspects of good teaching which I'm not yet even aware of.

But maybe the question of "what kind of teacher do I want to be when I grow up?" is a false one (if I could have just one more rephrasing of the question). I like to think that I'll always be "growing up" as a teacher, but never really arriving at some perfect understanding of what a great teacher is, or how to be this great teacher. Maybe the only "bad" teacher is a teacher who has stopped learning. And if that's true, then I'm okay with the fact that I have no idea how to be the teacher I want to be right now. It simply means that I have lots of time to learn from my students, from fellow teachers and from you - lots of time before I have to worry about running out of things to learn about teaching :)

When I Grow Up - Part 1

What do you want to be when you grow up? The answer was so simple when I was four years old - I would become a train man, an airplane man, or a nurse in a hospital. I have since decided that I should probably give up on the original plan of becoming a "man". And while I like trains, airplanes and helping people, it turns out that there are many other possible careers that I could also enjoy.

Right now, I'm in the very broad categories of "student" and "teacher" (which interestingly enough, does tend to involve train or airplane relative motion diagrams and a good deal of helping people). The past few weeks, I discovered some things I wouldn't have guessed about myself and my feelings towards teaching and learning; this has led me to feel quite certain that teaching (along with the related learning that teachers do) is a career that I can love. So I thought I'd share.

Life outside of teaching has been downright difficult lately. As I've been working through the ending of a relationship which mattered a lot to me, I've struggled to say goodbye to the hopes and dreams I had with someone whose dreams have changed. It has been challenging for me to redefine my value - not in a man's definition of my worth, but in God's, to strive to keep loving with my whole heart rather than building walls around it, to learn from the things I did wrong which contributed to this ending, but still forgive myself for the ways in which I wasn't the girlfriend I should have been, and to walk everyday with God. These things are easy to write down, but I'm finding they are much much more challenging to live. I've never experienced a broken relationship before, and God has a lot to teach me about love, grace and life. As I've been working through these things, I've felt a lot more sadness than I'm used to. So after our last weekend together, I was very worried that I wouldn't be able to teach well - that on top of everything, I would let my students down.

But an amazing thing happened last Monday. I walked into class with my bowl of gummies for our gummy bear circuit, my students said hi, and I just felt so much joy  (even more joy than I would feel if I had a bowl of gummies on a regular good day!) As the class went on, and I bopped around from group to group, I realized more and more just how much I love teaching. It actually almost made me cry, and I'm not a very leaky person.  It just hit me how blessed I am to be part of my students lives right now, as they're discovering who they are in their world - a blessing which is too easy for me to take for granted. It continues to surprise the socks off me: when I'm with my students, it's as if all of my concerns and sadness slip away. Of course, the things I need to work through are still there - that can't be avoided. But it has been a wonderful surprise to learn that teaching (especially with my students who are honestly such a dream class) really is a safe haven for me.

My science side can't help but look at this as a bit of a self-experiment. Somehow teaching continues to bring me joy even when my other work feels heavy and requires extra effort to complete. I think this suggests at least one good answer to the question of what I should be when I grow up. My dad, true to his funny engineer self, suggested (among other very loving encouragements) that I "re-calibrate" now that I'm on my own.  I won't dive too much into my relationship-recalibration thoughts on this blog, but so far my career-recalibration thoughts have been reaffirming the path I'm on. I truly do love teaching. I love seeing those beautiful aha moments when the student starts to piece everything together. I love being part of positive change, and teaching is all about growth and change - change in my students and change in myself. It's terribly nerdy, but as my poor friends who put up with endless demo's know, there is so much physics-happiness to be shared, and I just love sharing it.  And now I've learned that teaching brings me joy even when life is not easy. I really do have one of the best jobs a person could ever ask for.

The question of what I want to be when I grow up isn't fully answered yet, however.  The next aspect of this question is of course, "What kind of teacher do I plan to be?" I have a feeling, however, that this second question will require more words than the first, so I'll save it for another day.

Bicycle under a street light

Fun physics showed up on my bike ride home today! Did you know that you can pedal at the right speed to match the frequency of the street lights' flickering, so that the wheel appears to be not moving?

What's happening here? The streetlights are like very quickly flickering strobe lights - they "freeze" a moving object in time by taking many quick snap-shots. If the bicycle wheel is spinning too slowly, these fast snap-shots just tell the story of a rotating bicycle wheel - not very exciting. But if the bicycle wheel is spinning at just the right speed, the tread will have rotated exactly the right amount to appear to be in exactly the same position when the next "snap-shot" is taken by the street strobe light. Notice that this doesn't need to be a full 360 rotation of the wheel: the wheel just has to spin far enough so that the tread, say, one centimeter behind has now exactly taken the place of the tread ahead at the moment the street light flickers. 

These frozen "snap-shots" are really close together in time: the street light was flickering at a frequency so fast that the light just looked like it was continually shining to my eyes. So when I look down at my bicycle wheel, the series of snap-shots are put together smoothly, and my bicycle wheel appears to be still!

Here's an example of the same effect using a strobe light and a fan: http://www.youtube.com/watch?v=_3Fk5avi6kA. The key is just to match the frequency that the strobe is flashing to the angular frequency at which the fan blade is spinning, so that the fan blade is in the same location when each snap shot is taken.

For love and groceries

All you need is love... and groceries and rent and utilities and...

When it comes to physics and education, I have more than enough love. Indeed, friends, who endure my random "fun physics moments", might rather I restrain my physics love a little more. I'm currently trying to decide if I should pursue a PhD in physics education research or simply do a masters. I have no doubt that I would thoroughly enjoy the experience - I love the learning environment of the university, I love the research and I love the teaching opportunities. It would most definitely be a lot of fun to work on a PhD.

But I have to admit, love isn't the only factor in my decision. Tuition is higher and funding is lower than I'd planned for, and my practical brain can't help but wonder if a PhD would really be a financially sound decision.

So this semester will be an experiment. I just finished making advertising posters (using my sketch of the learning student, pictured to the left) for my physics tutoring services. I very much enjoy tutoring, so if I find it possible to break even this semester with some additional funds from tutoring, then I expect I'll be confident in diving into a PhD.

The key will be finding students who want regular weekly tutoring, not just cramming before the exam. I will try to be fairly strict about this anti-cramming policy. It's nearly impossible to learn physics in a short period of time just before the exam - it's like learning to play the piano - a student needs to work at it regularly and consistently throughout the semester in order to be successful. It would be terribly unethical for me to charge for tutoring if I didn't have sufficient time with the student to tutor effectively and consistently. As an aside, I do wish companies such as "CourseCram" felt the same way.

Now I know you're probably thinking, "Fabulous! As long as we don't hire her as a tutor, Anneke will finally stop inflicting her physics demonstrations with accompanying jazzy-hands on us." But you should know, I couldn't stop teaching physics to innocent bystanders if I tried. No one is safe from a fun physics moment! I'll try to differentiate between random free physics teaching and paid tutoring though through the degree of planning/preparation, building of ideas upon ideas and of course the direct connection to course material. Here's to hoping I have the heart to request pay to do a job that I enjoy perhaps even more than the customer...