Top 10 Blog Posts from 2019

It’s always difficult to pick the BEST of stuff. This is especially true when it’s all your own stuff.

So, let’s just say these are 10 nice posts from 2019.

How Does the Mandalorian See Through Walls?

You know I love to write about stuff that gets me excited—and I’m super pumped up about The Mandalorian (just finished season 1). In one of the episodes, Mando sees through a wall with his sniper rifle. How would that work?

side by side photographs showing boy holding up sheet

No, it probably wouldn’t be with infrared.

Modeling the Water from a Spinning Sprinkler

You don’t really understand something unless you can model it. In this post, I use python to model the motion of water shooting from an inward pointing and spinning sprinkler (based on the Steve Mould and Destin video).

This gif pretty much sums it up.

Orbital Physics and the Death Star II at Endor

This is my favorite thing to do (which I also did in the Mandalorian post above)—take some scene from a movie and and then use that as an excuse to talk about physics. In this case, it’s all about geostationary orbits from Star Wars: Return of the Jedi.

Bonus: more python code in this post. Double bonus, I use data from ROTJ to estimate the length of a day on the planet moon of Endor.

All Measurements Are Really Just Distance—or Voltage

I was in lab when I realized that pretty much all of our measurements were actually measuring distance. Well, originally that was true. Now we can make measurements by measuring a voltage.

Here are some measurement devices—this wasn’t in the original post.

You Can’t Calculate the Work Done by Friction

This was a post I wrote after a discussion I had with Bruce Sherwood. He told me this story about how it’s easy to use the momentum principle with a sliding block (with friction), but you can’t use the work-energy principle.

We like to think friction is this simple thing—but it’s not. The above image is an illustration to show that the distance a friction force is applied is not the same as the distance the object moves.

Video Analysis of Captain America vs. Thanos

There is the perfect scene in Avengers: Endgame. It’s not only perfect because of what Captain America does—but it’s perfect for video analysis. So, in case you haven’t seen it, Cap takes Thor’s hammer and smacks Thanos hard.

Here is the frame corrected version after using Tracker Video Analysis.

No, momentum is not conserved. But that’s OK.

What are Maxwell’s Equations?

Yes, Maxwell’s Equations can be tough.

an equation

Here is my attempt to explain these equations in a simple way to describe the electric and magnetic fields.

Every Jedi Jump in Star Wars

OK, not every Star Wars movie. I didn’t have Episode IX to include at this time (I will have to wait for the digital version of the video). But the idea is to analyze ALL the jumps. Here they are.

There are too many jumps for me to do a complete video analysis. Instead, I just estimated the jump height and the jump time. From these two values, I can make a graph—if the vertical acceleration is constant then there should be a linear fit.

The best part is that most Jedi have a vertical acceleration LOWER than g (free fall acceleration on Earth). Yoda has a vertical acceleration HIGHER than g because he takes so many short jumps. I need to write a future post just looking at Yoda.

All the Hacks and Science from MacGyver Season 3

Maybe this is cheating since it’s really not just one post. This is a list of all my science explanations for MacGyver Season 3. Oh, just to be clear—I’m the Technical Consultant for the CBS show MacGyver (season 4 starts in February).

It’s a lot of work to help the writers come up with new science tricks for MacGyver, but it’s also super fun. I also really enjoy making these MacGyver at home videos.

I’m really looking forward to sharing more science for season 4.

Projectile Motion in Polar Coordinates

I’ve had this secondary blog for over a year now—and I really like it. It’s like the old days of blogging. I can write whatever the heck I want (example—the top five lightsaber fights in Star Wars). Also, I can go into super complicated physics stuff.

Here is an example from my upper-level classical mechanics course. Can you use polar coordinates for projectile motion? Yes you can—but it’s obviously not the best choice.

newplot (3).png

There’s python here too.

Best Graphs from 2019

It’s a tradition. At the end of the year, I like to post “top” stuff. Here are my best graphs. I’m only going to share graphs that I created with Plot.ly—although there are some other ones out there. So, maybe I should say “best plot.ly graphs of 2019”.

Oh, you haven’t used plot.y? That’s OK. Plotly, is an online graphing platform. It’s pretty nice. The thing I really like is that you can create some data in python (with Glowscript) and send it over to plotly for beautification.

One last thing. I don’t yet know how many “best” graphs I have—I haven’t looked yet. Also, these are in no particular order.

What ball is the best to catch with during free fall?

Here is the graph.

The graph is from this post—https://www.wired.com/story/the-right-ball-for-playing-catch-while-skydiving/. The idea was to consider what ball would be best to pass back and forth while skydiving.

Modeling a Moon Run

Here is the graph.

This is from my post looking at the physics of running on the moon. Actually, I really like this stuff. I built a model of a running human in which the final running speed depends on the foot contact time with the ground. I really just made the model so that I could use it for this moon running post.

Oh, bonus—here is my python code for the running model.

All the Jedi Force Jumps

Here is the graph.

If you look at all the jumps (in all the Star Wars movies) you can measure two things—jump height and jump time. Assuming there is a constant acceleration (not necessarily true) then there is a relationship between time and height.

a = \frac{2\Delta y}{(\Delta t)^2}

So, by plotting twice the height by time squared, the slope of the line would give the vertical acceleration. In the graph above, the green line is for an acceleration of 9.8 m/s^2 (the value on Earth) and the red line is the average for all the Jedi. Notice that Yoda has a greater acceleration. I think that’s cool.

Oh, bonus video. Here are all the Jedi jumps.

Course Reflections: Introductory Calc-Based Physics (PHYS 221)

The Course:

This is the calc-based physics course (the first semester). The students in the class are mostly:

  • Physics majors
  • Chemistry majors
  • Computer Science majors
  • Math majors

I don’t think there are any other students that take this. OK, I guess you could include pre-engineering—but technically they are still physics majors.

For the textbook, I use the super alpha awesome book Matter and Interactions (Wiley – Chabay and Sherwood). If you’ve read my stuff, you should know that I LOVE this book (and Bruce Sherwood and Ruth Chabay are both great people to talk to). Here is my previous review.

Just a few highlights of the curriculum.

  • Includes relativistic momentum and energy.
  • Focus on fundamental interactions and fundamental particles.
  • Ball and spring model of matter.
  • Three big principles: momentum, work-energy, angular momentum.
  • Explicit inclusion of numerical calculations.
  • I use Standards Based Grading with options for students to submit reassessment videos.
  • We often use multiple-choice questions in class with student response systems (clickers). Matter and Interactions has a nice set of questions to use.

Here is the course website.

The Good:

I always enjoy this course. The students are both diverse and great. They are at LEAST in Calc-I so that means they can probably do some algebra stuff. There are a good number of students that are in even more advanced math classes like Differential Equations and stuff. Oh, and it’s a great chance to get to know the new physics and chemistry majors.

The class isn’t too big (mine started around 30) so that it’s fairly easy to memorize names.

Maybe the best part of the class is watching student videos. OK, I really don’t like watching videos—it can get kind of boring. But I LOVE seeing students make terrible videos and then get better and start figuring things out. It’s awesome when students have never made a video and are afraid to do it, but then really get into it.

Students eventually figure out that I’m not just assessing their videos, but they are learning by making the videos.

One other thing I liked—I always like it: speed dating physics problem solving. Here is a twitter thread on speed dating (from another class).

Also, I did assign and collect homework. I didn’t really grade it (I gave them a score), but it’s like free points and maybe it helps them practice.

One last “good”. I put together this video tutorial on numerical calculations that looks at an object falling on the surface of the moon. I think it’s pretty good. Not sure how much the students used it though.

The Bad:

Yes, there was some bad stuff. Sometimes I felt like students were just sitting there. Even when I was doing interactive activities, they had this blank stare (it seemed). Maybe it was the class time (9:30 AM)—although that doesn’t seem too early. I really don’t know what the problem was. For the most part they were fine.

Another big problem—speed dating. Oh, I get it. Students don’t want to participate. They want to just sit there and take in the fire hose of learning (they think that works). But in the end, most of them seem to get some positive things out of the speed dating. But the room was not super great for this. It’s a standard lecture hall—so I didn’t really have places to put boards. I tried using very small boards, but it just wasn’t perfect.

One final problem—a good number of student just never seemed to fully grasp numerical calculations.

The Future:

Here are some ideas for the future.

  • Mounted white boards. If I have to be in that lecture hall, I want to find some ways to put boards somewhere around on the walls.
  • Plickers. I’m ditching the TurningPoint clickers. I’m tired of constant updates that bork the system. I get it—they want me to upgrade. Not upgrading again. Oh, also with Plickers it shows the student name over their head when they vote.
  • More in-class stuff. More group problem solving. More activities. More focus on numerical calculations.
  • I should show the students more of the awesome physics (like stuff from my blog). I don’t do this enough because I get so busy with getting through different topics—but I think the students really like these things. Who cares anyway, it’s the stuff that I love.

Course Reflections: Intro Physics Lab (PLAB 193)

The Course:

This is the lab that goes along with the first semester of the algebra-based physics lecture. That means the students are mostly biology majors, industrial technology, or engineering technology.

This semester, there were only about 13 students enrolled. Here is a link to the course webpage. Over the years, I have learned that you really can just focus on one or maybe two big ideas during the semester. This time, I focused on:

  • Modeling with graphs. Collect data. Make a linear graph. Find the slope and interpret it.
  • Measurement and uncertainty. OK, technically I just used this during the second half of the semester.

The Good.

I can’t remember the exact paper—but there was a research paper that said physics labs don’t really help students. Oh, I found it.

Measuring the impact of an instructional laboratory on the learning of introductory physics (American Journal of Physics)

I feel like this gives me the freedom to do what I think will help the students the most. It doesn’t matter if I cover all the topics in the lecture. Yay.

With this in mind, I decided to start off with the marshmallow challenge. It’s basically a team-building and problem solving exercise in which groups try to create a structure to support a marshmallow as high as possible. I used this modified version – it’s great: https://shiftingphases.com/2019/07/08/hacking-marshmallow-challenge/

Other than that, here are some other things that worked well this semester:

  • Continued using end of class quizzes. Sometimes they seemed forced, but there were a couple of times that I made the quiz a sort of competition – like the projectile motion lab where they have to hit a target.
  • I think the numerical calculation lab went well. This could be better if I included the numerical stuff in more later labs. OK, technically it’s needed for the spring lab and the air resistance lab but normally students are too far behind to get to that part of the lab.
  • I think this lab on acceleration went fairly well. https://plab193.wordpress.com/2018/08/08/constant-acceleration/ . Students use a photo gate and a cart rolling down a track to get velocity as a function of time.
  • Finally, I cut down on the pre-lab instructions. Students weren’t reading them anyway. I tried short presentations – but I don’t think that really worked either.

The Bad:

Let’s just get to a list of notes here.

  • The thing that sticks in my mind is the extreme frustration I had with graphs. I feel like at the end of the semester, there were still many students that still didn’t understand graphing or the slope of a linear function. Help.
  • Lab reports were for the most part super terrible. Maybe I should just stop having them turn in a lab report.
  • The last lab of the semester, I asked them what they wanted to focus on. They said they were interested in a lab where they collect data on their phones (it was an idea I mentioned using the PhyPhox app). I went over some of the experiments, but I don’t think anyone really did anything.

The Future

Here are some ideas for the next time I teach this lab.

  • No more lab reports? Maybe move to some type of worksheet that the students turn in?
  • Maybe more learning activities – stuff like card sorts and speed dating physics problems?
  • More numerical calculations.
  • Go over the PhyPhox stuff and give them an explicit experiment.
  • What about using plickers at the beginning of class?

Course Reflection: Astronomy (EASC 102)

It’s the end of the semester, so that means it’s time to reflect on my courses. Why not just write this as a blog post? That’s what I will do.

The Course:

I’ve already talked about this course when I started the semester. So, here is a short review.

  • It’s a service course for non-science majors. There are no pre-reqs, so you can’t include much math.
  • The course was added late, there were only 13 students in the course.
  • I had a room that was more like a lab or a studio rather than a lecture hall.
  • As I said before, this is a tough class. The material seems fun, but it’s really deep. You can either cover superficial things—like known values of planets or you have to really get dirty. You can’t understand a star without knowing some important stuff about light and matter.

The Good:

The best part of the course was the flexibility. I could pretty much do whatever I wanted since they didn’t need anything from this course for future classes.

The other things that worked well were the labs. I mean, what the heck. Why not do a lab in the lab room? I started off with some of the University of Nebraska online activities—but I think these are too high of a level for my students.

After that, I went to make up my own labs:

  • Solar panels
  • Angular size
  • Parallax
  • I did a stellar properties lab – it was sort of a modified University of Nebraska lab.

I think the students liked the labs for the most part. Oh sure, there were a couple of students that just said “screw these labs—not going to participate” but there’s not much you can do about that.

Another thing I worked on was simplified presentations. The powerpoint slides that come with the textbook pretty much suck. They have too much stuff in them for the students to really learn anything. It’s not that my slides were much better, but I did include some of the online applets and animations in them.

Since the class was small, I had a better chance to interact with individual students. It’s always nice to get to know people. I admit that I didn’t learn names as well as I usually do.

In the last few weeks, I started using multiple-choice voting questions in class. I think this is the way to go. The questions I was using were probably too difficult for the students. Quick tip: use plickers (voting cards). When you scan the cards with your camera, it also shows student names.

Oh, one more thing. I think I did make some progress on student understanding of the nature of science. Really, this is the most important aspect of the course.

The Bad:

I already mentioned the bad powerpoints and the material is too deep. The other big problem—student understanding of graphs, math and stuff like that. It’s tough to do a lab that involves graphing when they can’t graph.

Although I had fun with the lectures, some students fell asleep.

The Future:

Let’s say I was going to teach this course again. What would I do? Here are some ideas.

  • Pick fewer topics. I think it’s best to stay away from stars and stuff. It depends on too many background ideas.
  • Do more labs. I would probably need to make the labs myself.
  • I think making some stuff that’s similar to PET would be perfect for this class. In fact, I did some labs like this for forces and waves.
  • I would like to do some type of project, but I’m afraid what the students would turn in.
  • DON’T USE the textbook or the powerpoints. They are terrible.

The Five Best Lightsaber Fights in Star Wars

The great thing about having a personal blog is that I can write about whatever makes me happy. Today, it’s Star Wars.

Actually, this was a question that my older son asked. What are the best lightsaber battles? I love these questions—they don’t really have just one answer so you can argue over who is right with no real winner.

Let’s get to it. If you don’t agree with this list—I’m ready for your complaints.

5: Darth Maul & Savage Opress vs Darth Sidious (The Clone Wars)

Just to be clear, this is from the Clone Wars animated series. This is my son’s favorite (he’s a huge Clone Wars fan). It’s pretty cool because it shows how powerful Sidious can be when he wants. Also, bonus points for the Dark Saber.

Double bonus, here is my son’s reenactment of this battle. Brace yourself.

4: Luke vs. Darth Vader (Episode V The Empire Strikes Back)

Yes, it’s true that this fight isn’t as dynamic as those in the prequels or the Clone Wars. I get that. Also, it’s possible that I just like this one because I’m older and this battle was so epic when it came out. But you have to admit that the cinematic quality here is awesome. Love it.

3: Qui Gon and Obi Wan vs. Darth Maul (Episode 1: The Phantom Menace)

This could be in the top five just because of the music. It’s also the first time we see how crazy a real lightsaber can get. I mean, before this all we saw was old men, half robot, and young mostly untrained warriors.

Also, it’s got a nice two vs. one AND a double light saber.

2: Obi Wan vs. Darth Vader (Episode IV A New Hope)

OK, this might not count. This is a fan-made redo of the battle between Darth Vader and Obi Wan on the Death Star. I guess it’s not canon in the Star Wars universe—but I can’t help myself. If this was how it originally happened, I would put this at number 1.

Oh, I was watching Episode IV the other day. When it came to the Vader vs. Obi Wan fight, I paused the movie and switched to youtube to watch this version.

1: Obi Wan vs. Darth Maul (Rebels)

You might not like Star Wars Rebels—I get that. It’s sort of like a combination of Aladdin and Star Wars. However, there are some really great parts in this show. When Darth Maul finds Obi Wan and tries to kill him—this is just the best. It’s not about the light saber action, but it’s still just the best.

Modeling a Spinning Sprinkler

Subtitle: “You don’t really understand something until you model it”

Here is the video. It’s great. Watch it.

The basic idea is to predict the path of water that is shot from a spinning sprinkler. In the first case, the water is shot straight out of the spinning pipe. The second case is a little bit trickier with the water shot towards the center of the sprinkler. OK, it’s not actually a sprinkler.

Of course, once a drop of water leaves the sprinkler, it will only have the gravitational force acting on it. So, if you view this from the top—a drop of water should travel in a straight line with a constant velocity. But there is a problem that makes this difficult to predict. It’s that we don’t see the path of one drop of water, we see the path of a water stream.

A water stream is a collection of water drops. Even though one drop might travel in a straight line, the next drop will be “launched” at a different location with a different velocity. This makes it look weird.

OK, so let’s get to a model. I’m going to go over the steps to build this model in VPython.

Build a bar

Don’t try to do everything at once. Let’s just make a spinning bar—I’ll add water balls later. Here is what that spinning bar looks like.

And here is the code (along with a link to the code – https://trinket.io/glowscript/d6545ddfca

Let me go over some of the important parts of this code.

  • The bar is an object of type “box”—this is a prebuilt object in VPython. It has two important attributes. The position (pos) is the location of the center of the box. The size is the vector with length, width, and height.
  • I added a ball so you can see the center (it’s not needed).
  • The variable “omega” is the angular velocity of the rotation. You can change this if you like.
  • The variable “theta” is the angular position of the bar—this is used for something later.
  • In the loop, the rate(100) tells the code to not do any more than 100 loops per second. Since I have a time step of 0.01 seconds, this means 100 loop would take one second—it would run in “real time”.
  • Don’t worry about line 16 (update theta)—at least not for now.
  • Line 18 is the important part. There is a rotate function in Vpython. You need to pick the angle (in this case it’s dtheta which is the angular velocity times the time step), the axis of rotation (the z-axis) and the origin of rotation (the origin).

But it works.

Add a single water

The next step is to add a single ball of water to the end of the sprinkler bar. It’s not going to do anything except to “ride around”. Here’s what that looks like. It’s really the same thing except with that ball of water.

Here is the code—https://trinket.io/glowscript/14e1ecbb7d. Let me just point out the important parts.

If I know the angular position of the sprinkler, I can find the vector from the center of the sprinkler to the end of the sprinkler. It looks like this:

\vec{r} = \left(\frac{L}{2}\right) <\cos\theta,\sin\theta,0>

For each iteration of the loop, I can calculate theta and then use that to calculate “r”. This r is now the new vector position of the ball.

List of balls

Now for the magic. Lists are your friend. I feel like I could write a whole post on just lists—but I want to get right to the good stuff.

In short, a list is a group of things in python. Let me start with an example program.

balls=[]
x=-5
dx=1

while x<3:
  balls=balls+[x]
  x=x+dx

print("balls = ",balls)
print("balls 3 = ",balls[2])

Here are some notes on this code.

  • balls = [] makes an empty list. The name of this list is balls.
  • In the loop, I add a new x value to the list and then update x.
  • At the end, I print the list of balls and the 3rd item in the list (the first item would be balls[0]).

Here’s the output.

But wait! You don’t just have to make a list of numbers. I can make a list with objects too. Check out this version of the code.

balls=[]
x=-5
dx=1

while x<3:
  balls=balls+[sphere(pos=vector(x,0,0), radius=0.1,color=color.cyan)]
  x=x+dx


print("balls 3 position = ",balls[2].pos)

Here is the output.

Boom. Check that out. It’s 8 balls—but in just one list. You can even print out the position of one of the balls (you can’t print the whole list because a sphere() isn’t printable).

Water balls in a list

OK, I think we are ready. Oh, you might not be ready—maybe you need some more practice with lists. Just start playing around and see what happens. Anyway, here is the plan.

  • Make a list of water balls (actually two lists—one for each side).
  • Start the time (t = 0) and a time step of dt.
  • Set a ball time counter. If the time gets to some specified value, then create a ball and add it to the list (both lists).
  • When you create a water ball, set its properties: mass, size, add a trail…oh, and initial velocity. Yup. You can do that.
  • Now let stuff run. I will need to go through each ball list and update the water ball positions, but that’s not too difficult.

Let’s just get to the code. Here it is (also on trinket.io)

GlowScript 2.9 VPython

#Length of sprinkler - just leave this
L=0.1
stick=box(pos=vector(0,0,0), size=vector(L,.05*L,.05*L),color=color.yellow)
cent=sphere(pos=vector(0,0,0), radius=0.03*L, color=color.red)


#CHANGE THIS - rotation rate of sprinkler
omega=2*pi/2


theta=0

#CHANGE THIS to -1 to make balls shoot IN
a=1 

t=0
dt=0.01

#this is just a spacer to make the scene look nice
space=sphere(pos=vector(4*L,0,0),radius=0.001)


#water stuff
water=[]
water2=[]
vwater=.3
tint=0 #this is the "clock" for shooting water

#CHANGE THIS - this is the water ball production rate
f=15 #water per second rate that balls are made


while t<10:
  rate(100)
  r=(L/2)*vector(cos(theta),sin(theta),0)
  r2=-r
  

  if tint>=1/f:
    
    water=water+[sphere(pos=r,radius=0.04*L, color=color.cyan, v=(-1*cross(r,vector(0,0,omega))+a*vwater*r.hat),
    make_trail=False)]
    water2=water2 +[sphere(pos=r2,radius=0.04*L, color=color.cyan, v=(-1*cross(r2,vector(0,0,omega))+a*vwater*r2.hat),
    make_trail=False)]
    tint=0
  for ball in water:
    ball.pos=ball.pos+ball.v*dt
    if ball.pos.mag>3*L:
      ball.v=vector(0,0,0)
      ball.visible=False
      del ball
  for ball2 in water2:
    ball2.pos=ball2.pos+ball2.v*dt
    if ball2.pos.mag>3*L:
      ball2.v=vector(0,0,0)
      ball2.visible=False
      del ball2  
    
  theta=theta+omega*dt
  
  stick.rotate(angle=dt*omega,axis=vector(0,0,1), origin=vector(0,0,0))
  t=t+dt
  tint=tint+dt

This is what the output looks like. Actually, this is an animation for the case of the water shooting inward (since I already had the gif).

Now for some comments on the code.

  • When the water ball gets a certain distance away (I think I set it to 3*L), I change the water ball velocity to vector(0,0,0) and then I make it invisible. Otherwise the view would just keep expanding and it would look weird.
  • I don’t have any other important comments, but I can’t have a one bullet list.

I think that’s good enough. Hope that helps.

Angular Size Lab

Enough was enough. I couldn’t handle going through the chapters in the introductory astronomy course. It was too much material and it was too fast. But I’ve already complained about this in a previous post.

I didn’t have much time to prepare, but I decided to do a lab activity in class. My idea was to have the students build something to measure angular sizes. They could then use this device to measure the size (or distance) of various objects outside. I figured it would be fun to have them actually build things.

So, here is the plan. Step one is to go over the math of angular size. That includes the relationship between the circumference and radius for a circle.

C = 2\pi R

Another important idea is the relationship between the angle in degrees and radians. We need to measure angles in radians, so I also explained this relationship with 360 degrees equal to 2*Pi radians.

The next part was to build an angle measuring device. I’ve done the before in a physics lab, but I wanted something a little simpler. Here’s what I suggested to the students—make some small “flag” that you can hold at arm’s length (so that the distance from eye to flag is constant) and use this to measure angles.

I gave them popsicle sticks and sticky notes and a bunch of other stuff (with the hope that they would come up with their own design). In the end, they had something like this.

This is just a sticky note on a pencil.

The next step is to “calibrate” this instrument. Put your eye a known distance (say 5 meters) from a known length. I had the students use bricks in the wall or put tape on the wall a set distance apart. From this, they can calculate the angular size of the object and make markings on their device. Oh, this diagram might help.

The distance from the eye to the object is R and the length of the object is L. If the object is small compared to the distance, then this length is approximately the same as the arc length of that part of a circle. The value for theta can be determined by dividing L by R.

Now repeat this for another object so that you can turn the angle measuring device into something useful with multiple markings on it. Now we are ready to collect some data.

Here is a large light for the football stadium, you can see it right outside the classroom.

I used Google maps to get the distance to this object (it’s 240 meters) and then had them measure the angular size and calculate the width.

Here are some other questions:

  • What is the angular size of your thumb at arms length?
  • What is the size of a sign on a building across the street?
  • There is a doorway down the hallway. The width of the frame is 0.91 meters. How far is it?
  • What is the angular field of view of your phone’s camera?

Overall, the lab went fairly well. Students have a bunch of trouble with that first step—where they build something. You can tell they don’t feel comfortable without explicit instructions.

Let’s talk about carbon dioxide

OK. Here’s the deal. I have lots of emails about my recent post. The post was a back of the envelope type estimation to see what would happen to the carbon dioxide in the atmosphere if everyone planted a tree.

It’s just a rough approximation. Here’s the post.

https://www.wired.com/story/plant-a-tree-for-climate-change/

Basically, I estimated the size of a typical tree and then figured out how much carbon dioxide you would need to make that tree. After that, I estimated the number of particles per million (ppm) of carbon dioxide.

Here’s the code for my calculations – https://trinket.io/glowscript/f7edb65694

Now for the rest of this. Lot’s of people have sent me comments. If you want to talk about this – here is your chance. Comment on this post. Another option: comment on twitter. Here is a good thread.

If you email me, there’s a good chance I won’t reply. These two options are your best bet.

Intro Astronomy Update

I picked up this introductory astronomy course just a week before classes started. One of my other classes didn’t have enough students in it, so I got this instead. It’s a gen-ed science course for non-science majors. Since it was added late, there are only 12 students in the class.

I’ll be honest—there are some super awesome topics in this intro astronomy course. The historical stories and the “how do we know” stuff is great. HOWEVER, it’s also a really tough class.

I didn’t have time to build something from scratch, so I just went with the order and presentation of topics according to the textbook. This class uses Explorations – an Introduction to Astronomy, 9th ed (Arny, Schneider) McGraw Hill. It’s an OK, text with only a few areas that I don’t agree with. But let’s look at the first 4 chapters:

  • Chapter 1: The sky. Celestial sphere, motions of the sky, seasons, phases of the moon.
  • Chapter 2: Historical astronomy stuff. Mostly, this is the geocentric vs. heliocentric model of the solar system.
  • Chapter 3: Gravity and Motion. BAM. Forces and motion, gravity, escape velocity.
  • Chapter 4: Light and atoms. DOUBLE BAM.

Chapter 3 is bad. I mean, I have other classes that spend about 1/3rd of the semester on forces and motion and they don’t even get to the 1 over r squared version of gravity at any point. I think it’s possible to get students to understand most of the ideas in chapter 3, but not in a chapter-length amount of class time.

Oh sure. You could just tell the students everything they need to know about forces and motion. You could TELL them that a constant force makes an object have a constant acceleration. But research shows that this doesn’t really work. No, this is a tough concept and it’s going to take time to get it figured out.

Chapter 4 is even worse. The interaction between light and matter could be its own separate course. It’s not just a chapter. Oh, on top of that – there are these instructor power point slides. Here are three in a row that go something like this.

  • Light is an electromagnetic wave.
  • Light is also a particle.
  • Which way light manifests itself depends on the situation.

That’s bad. Of course you know I don’t like the whole “light is a particle” thing.

OK, but there are some good things about this course. I have a small enough class that I can put in some extra stuff. We did some of the NextGEN PET units in class, and that went over fairly well. I have also been doing some of the great online labs from University of Nebraska-Lincoln (https://astro.unl.edu/naap/). Those are nice.

One other quick note. I think I am going to skip over all the planet stuff. It seems like it would just turn into a “memorize the density of Saturn” stuff. I really want to get to stars. There are some great stories about how we know stuff about stars.

I’ll keep you updated on the progress of the course.