Perhaps you haven’t noticed, but I’ve been trying to make a bunch of physics videos. Oh, sure—I already have a ton of stuff on youtube, but it’s not linear. For my old stuff, I will solve a problem on work-energy and then do electric field stuff and then go back to kinematics. It was just whatever topic came up in class or online or whatever.
I figured I should start over and do a whole physics course—well, not EVERYTHING. No, I would do just enough to get you through the course. I hope you get the title now. Also, this is the title of that self published ebook I wrote a long time ago—since it really is the video version (but updated).
So, where am I now? I’ve got 4 chapters completed. I think it’s a pretty good start. Here are the chapters (as playlists) along with descriptions.
Chapter 1: Kinematics
Notice that I started off by making a title screen and all that cool stuff. I will end up dropping this so that I can make videos faster. Also, in my previous videos I was in front of a whiteboard. In this case, I’m writing on paper. Still not sure which way is better.
In this chapter:
Constant velocity in 1D.
Example of constant velocity.
Introduction to numerical calculations (1D constant velocity).
Constant acceleration in 1D.
Numerical calculations with constant acceleration (in 1D).
Solving the “cop chasing a speeder” problem.
Chapter 2: Forcesand Motion
It’s tough to start in physics with forces. There are so many things to cover. This is a shorter chapter that looks at the fundamental ideas of force and motion.
Introduction to forces and motion. I really like this first video. It’s a conceptual look at the forces, the momentum principle and “Newton’s 2nd Law”. Guest appearances by Galileo, Aristotle, Newton.
Forces in 1D – falling objects.
Modeling the motion of a mass on a spring (and finding the model of a spring force). This one is long (but pretty nice).
Chapter 3: Vectors—2D and 3D Stuff.
The goal here is to expand kinematics into using vectors—but then you need to know about vectors.
Intro to vectors.
Kinematic equations with vectors.
Example of constant velocity and position update formula in 3D.
Intro to projectile motion.
Finding the range for projectile motion.
Numerical calculations for projectile motion.
Acceleration of a block on an inclined frictionless plane. This is an example of forces in 3D.
The physics of flying R2-D2. Using forces and air resistance.
Chapter 4: Calculated Forces
There are really two kinds of forces. There are forces that have an equation to determine the vector value (these are calculated forces). Then there are forces that don’t have an explicit equation (forces of constraint). This chapter just focuses on calculated forces.
Example of gravity—calculating the net force on the Apollo 13 spacecraft.
Introduction to visual objects in VPython. This is a setup for the next video.
Modeling the motion of an object near the Earth.
Modeling the Earth-moon system.
Mass on a spring (again) – but this time with visuals AND 3D motion.
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?
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 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.
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.
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.
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.
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.
In order to keep my blogging certification up to date, I am required to post some type of year end review.
OK, here it is. These are my “best” or “favorite” posts from 2018. Maybe these didn’t get the most traffic, but they are ones that I like the best. It’s all about me.
You might think this list is long, but I just counted. I had 106 blog posts for the year of 2018. So, these all “made the cut”. Also, I normally just list the posts but this time I will give a brief description.
Really, this post is all about a TV show – The 100. In one episode, a boy is floating around in a space ship during the re-entry process. This leads to a discussion about how gravity works and what happens during re-entry.
This really isn’t a blog post—at least not like a normal post. This is really just a holder for my WIRED video on how airplanes fly. This short explanation covers flying using the momentum principle instead of Bernoulli’s Principle.
The gravitational constant is needed to find the gravitational force between two objects with mass. The problem with finding this value is that it’s very small and we (humans) didn’t initially know the mass of the Earth.
Here is a method to find the gravitational constant by estimating the mass of a mountain and detecting the change in gravitational field with a pendulum. It’s just so crazy it might work.
Oh, the real tricking part is find the direction of “up” and “down”.
Everyone knows (or should know) how much I love numerical calculations with python. Here is a demo to show the angle of reflection is equal to the angle of incidence using Fermat’s Principle. This says that light takes the path of shortest distance.
First, there is a random walk. Second there is a random self-avoiding walk (SAW). A self avoiding walk doesn’t cross its own path. So, a SAW is like a long protein—which is important for life.
3D works the best for proteins (and not 4D). In 4D, there is no big difference in length vs. step number for SAW and normal walks. In 3D, it’s more likely a walk will cross itself—which is important for protein folding.
Yes, there is lots of python code here. Note: random walks in 4D are tricky since you can’t just use the position of the walk as a built in 3D vector class.
This is one of my blog posts that goes along with an episode of MacGyver (since I’m the technical consultant for the show). The idea was that MacGyver would use some stuff from a car to find out how to get to a base from his location in the desert.
The cool part is that navigation is really just using a compass to measure angles and clock to measure time.
Note: for this particular episode, I did a bunch of calculations to get the exact angle and time measurements they would use in the show. I don’t think they made it in the episode, but I did it. Also, I had to cheat since everything happened at night and MacGyver couldn’t find the time of local noon.
Yes, a Star Wars post. SPOILER ALERT – there is a space battle in Star Wars The Last Jedi. They show this First Order ship firing on the Resistance. In order to make it look like a WWII sea battle, the turbo lasers have an arc to them—that looks cool, but it wouldn’t happen.
So, what do I do? Other than enjoy the movie (which I do), I first do a video analysis to determine the vertical acceleration. Then I make a python model to recreate the arc. Fun.
In Star Wars A New Hope, there is a scene that shows the escape pod leaving the blockade runner (near the beginning of the movie). It turns out that this shot was created by dropping a model and viewing it from above.
Here is my video analysis (with angular size) to show that the model is indeed accelerating as it moves away.
Bonus: one of the guys that made this special effect sent me an email after I posted this. Winning.
I started off writing a book review (How to Invent Everything: A Survival Guide for the Stranded Time Traveler – Ryan North). In the book, he suggests that if you were starting from scratch it would be easier to build a radio transmitter than it would be to build a clock. Of course (from a previous post), a clock is important for navigation. If you had a radio transmitter, you could just broadcast the time.
OK, but how difficult is it to build a transmitter? Not too hard. I did it. Here is my spark gap transmitter.
Why are you still here? Oh, you are waiting for just one more post? Or maybe you think this was too many? No, it’s 16 out of 106. That’s just 15 percent of my posts.