PHYSICS! Now that I have your attention, let’s go over the important points. I’m currently an associate professor of physics at a public university. But wait! That’s not all. I’m also a blogger at WIRED and Medium along with videos on youtube (Dot Physics). Oh, there’s Instagram too.
Oh, you want to reach me to ask a physics question or suggest a blog topic or share a cool video? Maybe you want me to give a talk (that’s possible) or media inquires or maybe some science (or sci-fi) consulting? Here’s my email: rhettallain AT gmail DOT com.
“The circle is now complete. When I left you, I was but the learner. Now I am the master.”
That’s what Darth Vader said when he encountered Obi-Wan Kenobi in Star Wars Episode IV. This is how I feel about our Mathematical Methods course. I remember taking an undergraduate course AND a graduate version. I was clearly “but the learner”. Now, I am ready to be full master. I’m not even going to use a textbook (because none of them really fit the course).
Instead of a textbook, I’m going to list my topics for this course (along with any resources that I have). If you like, you can think of this blog post as my textbook. Oh, but it’s a living textbook. I’m going to modify this throughout the semester to match what’s going on in class.
OK, let’s get to it. Oh, most of these links are videos.
Photo: Rhett Allain. STEM Fest at Southeastern Louisiana University
It’s something the we do every once and a while. There will be some event for middle to high school students that has something to do with science. So, the department (Chemistry and Physics) will set up some type of demo stations for the kids. Usually some of our physics and chemistry majors are in charge of interacting with the younger kids. It’s a great opportunity for our majors.
But there are some demos that work well and some that don’t work so great. Recently we participated in STEM Fest. Basically a whole bunch of “vendors” set up tables for kids to come by and see science stuff (Science Technology Engineering Math). With that, you want a demo that can meet the following conditions:
Relatively easy to set up (no particle accelerators).
Visually attractive to normal humans. Something that could be seen from a distance that a person might say “hey, what’s that? Let’s check it out”.
Has some type of explanation that can at least START a discussion about science. Hopefully something that our chemistry and physics majors could use to engage in a conversation.
It would be nice if it could engage multiple (maybe like 5-10) kids at one time.
With that in mind, I want to go over the stuff we used (and some things I saw other tables using) and talk about how well they worked. In a future post (or multiple posts) I would like to give a more detailed description of each demo with key ideas for our students to use in when starting a conversation.
Liquid Nitrogen Balloons
Photo: Rhett Allain. Chemistry major pulling a balloon out of liquid nitrogen.
Fortunately, we often have left over liquid nitrogen in our department. This demo could be anything—but we normally take a bunch of balloons and stuff them into the cold liquid so that they shrink. When you pull them out, they expand. It’s very visual and quick to perform. You can also put some liquid nitrogen in a styrofoam cup and let student blow air onto it. This cause the cold air in the cup to move and make water vapor (plus they can feel it).
Overall, this is a pretty good demo. It was a big hit at STEM Fest. Really, the only bad thing is that you need liquid nitrogen. If you don’t have that, then you don’t have anything. In terms of setup, we did bring the large dewar of liquid nitrogen, so that’s a little bit of a pain—but the balloons are small and cheap.
Dry Ice Bubbles
Photo: Rhett Allain. Chemistry student making bubbles with dry ice.
I really didn’t pay too much attention to this demo. I think it’s a flask with dry ice connected to a tube with a funnel on the end. When you dip the funnel into soap, the expanding carbon dioxide fills the balloon. Simple.
This looks easy to setup, but it didn’t draw as big of a crowd as the liquid nitrogen. But it’s so easy to do that it seems like a nice one to include.
Concave Mirror
Photo: Rhett Allain. Concave mirror plus an LCD monitor without the polarization screen.
We have this large parabolic mirror. My intention was that kids could use this to project an image onto a piece of paper (I made a small frame to hold tracing paper). But you can also just look at it and see a real image of your hand (it looks like you can grab your own image).
This should always be included with demos. It’s super easy to set up. You just need to put it where people can see and they will often figure out their own demos to do with it. The screen projection didn’t really work—you need some type of very bright source to make a projection.
I would like to make one modification to this setup. If there was some kind of marker (like a ring stand) at the appropriate location for the viewing location, it would be easier to see how to grab your hand image. That seems easy to set up.
Polarized Light and an LCD Monitor
I have an older LCD monitor with a the front polarizer removed (a student did this for me a while ago). There’s a large (external) polarizer. When students hold this up, you can see the image on the monitor. Without the external polarizer, it’s just a white screen. Oh, I’m running an old Apple TV with a screen saver to produce an image.
Again, this is pretty easy to setup (assuming you have electrical power). It’s not super appealing from a large distance, but when kids get up close they seemed to enjoy it.
Chemistry Gak
I didn’t have anything to do with this demo (you know, chemistry). Basically, kids come by and mix together stuff to make gak (a type of fun putty or something). The kids like it, but they have to sit down for a moment to make the stuff. You could probably do about 3-4 students at a time.
You can’t really see this demo from far away. A human would have to decide to go up to the table to figure out what’s going on. Also, it requires a bunch of supplies to be carried into the event. However, in the end the kids get something to take away (the gak). We always do this one.
Vacuum Bag
We didn’t do this one, but I saw another group use it. The idea is to take a human and put them in a large plastic bag (with their head sticking out). Then you use a vacuum cleaner (or pump) to remove the air from the bag. The atmospheric air pressure then locks the person in place and they can’t move.
It’s a great demo, but not really for large crowds. It takes a few minutes for a person to work through the demo and other people can just observe. Also, it sort of scares me. A kid could get freaked out or have trouble breathing. Even worse, they might try this one on their own and do it wrong (and dangerous).
OK, there are more demos—but those are the ones we used recently. Next time we have an event, I will add any new stuff we used.
At the end of each semester, I like to think about what worked and didn’t quite work for each of my classes. In this case, it’s the dreaded summer session (yes, it’s very intense). I had 2 introductory physics lecture courses and two labs.
The summer session takes place from the beginning of June to the end of July. Lecture courses meet Monday-Thursday for 1 hour and 15 minutes. Labs meet every other day (twice a week for both) for 2 hours.
The enrollment this summer was way lower than previous years. Actually, last year dropped from the previous years also. I’m not sure there will be enough demand for these courses next year (which means I will need to find something else to do).
For the lecture courses, we use College Physics 5th ed (Giambattista). We have an agreement with the publisher to use the online version of the textbook along with their online homework (both of which mostly suck in my humble opinion). Oh, the textbook is OK—just not the ONLINE version.
Algebra-Based Intro Physics
These are our introductory algebra-based physics courses. The students in the course are mostly biology, engineering technology, industrial technology, and kinesiology.
Physics 1 (it’s not actually called that). This course covers forces, energy, momentum, and torque (maybe angular momentum also). It’s pretty much your standard first semester physics.
I did make chapter summary videos (which I think are fairly nice). Here is my video playlist with the summaries and sample problems (playlist).
Physics 2. The second semester of physics traditionally covers electric fields, magnetic fields, DC circuits, AC circuits, light, optics. Personally, this course is a bit of a train wreck. We try to teach all these awesome things (electric and magnetic fields and their relationship) but without the calculus to back it up. In the end, the textbook just becomes a series of equations that might as well just be magic incantations of physics. I sort of hate it.
My goal for Physics 2 was to transform it into more of a physical science type of course with added calculations. I figured that it would be better to look at a wider range of ideas and include an emphasis on energy and power (real world stuff). I would love to rewrite the curriculum to focus on this, but of course I didn’t have enough time before the semester started.
So, as a compromise (with myself) I ended up with the following:
Electric field / electric potential – just the very basics. I didn’t do any weird stuff that requires unit vectors for the electric field.
DC circuits. Again, nothing crazy in terms of solving circuits.
Magnetic fields and forces. You are pretty limited here in terms of calculations. I just did loops and straight wires.
Faraday’s law and stuff.
Light and electromagnetic waves.
Optics
At the end I included a lot of fun stuff in astronomy (the students liked that).
Here are my chapter summaries and sample problems (playlist).
Let’s talk about grading. Normally, I would give short in-class standards and allow students to submit video reassessments. However, this semester I decided to JUST do video reassessments since the classes were small. Oh, I don’t know if that was a good idea or not. But I did it.
There was also assigned homework problems from the book. Students worked these out on paper and uploaded images to google classroom (which works great)—I then grade them manually. Of course, I mostly just gave full credit for the HW but they aren’t worth many points. I like the HW grade because it gives students some structure in their study schedule. This way, they have an idea of what and when they should understand some stuff.
There was also a final exam. I don’t know if this was the best idea since they didn’t have any other in-class assessments, but it was there. Some students scored quite well on the exams but others did very not well.
Other random thoughts:
In the past, I have required students to do some type of numerical calculation (it doesn’t have to be with python). I didn’t do that this semester—although I did go over this quite a few times in class.
I love speed dating problem solving (where students work on problems in different groups). However, with such low numbers in class it was rather difficult to get this to work.
For the start of most classes, I liked to show some interesting application or real world example of physics. These were fun for me, but I think the students liked them also. Maybe I will put together a list of the start topics.
Oh, during the first week of class I was out of two for 3 days (APS conference). Originally, I was going to have someone cover for me but that fell through. Instead, I just posted some online lectures and practice problems. This is not a great way to start the semester.
Before the semester, there were students that asked about an online class. I think this is a terrible idea (from a learning perspective). However, a chemistry had an online version of the course this summer and enrollment was huge.
For the future, I would like to start fresh in terms of curriculum. That’s my plan at least.
Physics Lab
There are two labs that go along with the two intro physics courses. I sort of messed these up this semester.
Since the summer schedule is brutal, I decided to split each lab into two days. For the first meeting, I would show them a all the physics and equipment. The second day would focus on “project” day where the students would create their own lab experiment to use for a write up. I told them they could work online with some material if they liked. The emphasis here was on creative and real-world labs.
Honestly, there were some students that did some awesome stuff. I was super impressed. Other students used the project day to just skip the first lab day and do the most basic lab that I suggested (disappointing). The lab report were mostly uninspiring (except for a few shining stars).
For my Intro Physics course (algebra-based), I created video summaries for each chapter. These are created to accompany College Physics (Giambattista 5th ed – McGraw Hill).
Here are the videos for the first semester (mechanics):
So, there’s this machine that Tesla made (just in case you weren’t following the previous episodes) called Sheva. It was used as a type of directed EMP device to destroy electronic stuff.
Aunt Gwendolyn says that it’s not just a weapon. It’s also a renewable power source. OK. Let’s just assume that Tesla figured out something that no one else figured out. I’m fine with that.
However, you can’t get energy for free—like, never. If you want to produce some electrical energy output, SOMETHING has to decrease in energy. It is the way. Even with a nuclear power plant, there is a change in mass energy (from the thing).
What about renewable energy? Really, this just means the original source of the energy is something we don’t care about. If you use solar panels on your house, you can get electrical energy. This comes from the Sun—which is basically a giant nuclear fusion power plant. But who cares if the Sun decreases in mass? It’s really not our problem. So, solar panels aren’t giving you “free energy”.
OK, so what about Sheva? No one knows. That’s why this is such a great weapon/tool. Maybe it gets energy from the interaction between the Earth and Sun’s magnetic fields. Perhaps it has something to do with other dimensions. Clearly, it’s not just hand-crank powered. That wouldn’t give enough energy for an EMP and it wouldn’t be renewable. The mystery is why it’s cool.
Nuclear Critical Mass
There’s a bunch of stuff here, so let’s start with the most basic part. What is nuclear fission?
OK. Suppose you have a big atom. Let’s say it’s Uranium-233 (this means it has 92 protons and 141 neutrons in the nucleus). If you throw a neutron at this atom, it becomes unstable and (usually) breaks into Xenon-137, Strontium-94 and 3 neutrons. The mass of all this stuff is less than the mass of the U-233 with the lost mass being converted to energy.
If you have just one uranium atom, you just get a small amount of energy. But if you have a whole bunch of uranium atoms, you can get a chain reaction from those neutrons. How many atoms you need for a chain reaction is the critical mass.
Sheet Metal to Protect from Missile.
A missile is inbound to hit the warehouse with MacGyver and Riley. MacGyver takes a piece of sheet metal to cover both of them inside a small inclosure. The missile hits. Boom. Explosion. Fire.
Would this work? There are three things you have to worry about with an explosion:
Projectile debris. Stuff gets flung all over the place. If this stuff hits you, it’s like getting shot with a bullet (or worse).
Pressure wave. The explosion creates a change in air pressure that pushes outward. This pressure wave can seriously destroy the insides of humans.
Fire. Sometimes, there is also fire.
The sheet metal and the enclosure would surely give some protection from the projectile debris. It might also protect from fire. It wouldn’t do too much against the pressure wave. However, for an unconfined explosion the pressure wave expands in all directions and decreases in damage as it gets farther away. If they aren’t too close, they might be able to survive.
Destroying a Nuclear Bomb with a Conventional Explosion
So, there’s a nuclear device. It’s going to explode and destroy a dam. The dam will flood a volcano. The volcano explodes and covers much of the Earth’s atmosphere with volcanic ash to make things bad. That means MacGyver needs to stop the nuclear explosion.
Really, you don’t need some super secret knowledge to make a nuclear bomb. Pretty much everyone knows how to do it. However, it’s still difficult. You need the following two things for a nuclear weapon:
Nuclear material.
Precise engineering.
The key is to get a nuclear chain reaction started. The reaction is almost always (but not always) initiated with conventional explosives. It has to be JUST right to get the thing to go nuclear.
If you put a conventional explosive near a nuclear bomb, it can disrupt the very delicate start of the chain reaction. Of course, it’s still a bomb—so, that’s not good. Also, much of the stuff in the nuclear bomb is radioactive and you will have just spread that all around the place, that’s also bad. But it’s better than a nuclear device.
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