# Best Posts for 2018

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.

Let’s do it.

There is indeed gravity in space. Common ideas about gravity.

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.

Flying planes with tiny collisions.

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.

Finding the gravitational constant with a mountain.

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”.

Calculating the angle of reflection with a numerical calculation.

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.

So, python code just “shoots a ball” at different angles and then calculates the travel time. Check it out. https://trinket.io/glowscript/1e2a30cab5

Why is it so difficult to predict where a satellite will crash from orbit?

Here is another numerical model (python) to show that with slightly different initial conditions, the Taingong-1 spacecraft will crash at a different location. Code included.

Random walks in 1D, 2D, 3D, 4D—and why we live in 3D.

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.

Video analysis of a race with The Freeze.

The Freeze is this guy that races mere mortals on a baseball field. He’s fast. Very fast. He gives the victim a head start and still wins. So, here is my analysis along with some physics homework.

Celestial navigation with a protractor and a watch.

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.

Modeling the trajectory of turbo lasers in The Last Jedi.

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.

Oh, here is the code. Also, I think I did this same type of thing with TIE bombers from Empire Strikes Back. Maybe that should have been in this list too.

Some science communication mistakes are worse than others. I’ll just leave it at that.

Physics model of a running human.

How do you model the motion of a running human? How do you take into account the idea that they can’t keep speed up forever? Here is my basic model.

• Humans are like a ball that impacts with the ground.
• When a human hits, they can only exert some maximum force to change the momentum.
• The vertical component of this force pushes them back up to keep them in the air for some amount of time.
• There is a minimum time the human must be in the air to switch back and front legs.
• The faster the human runs, the lower the ground contact time.
• Eventually a human reaches a speed such that the contact force is only up and not increasing the speed anymore.

I really like this model. It makes me happy. Code included.

Does the Sun orbit the Earth or does the Earth orbit the Sun?

OK, we all know the Earth orbits the Sun. But how can you tell? Here’s the answer. Oh, and I also include a python model of retrograde motion.

Boiling Water at Room Temperature

What is boiling? Great demo. You should try this yourself.

What’s the difference between mass and weight?

This is a surprising confusion for students. Here is an explanation of mass vs. weight. Also, here is a great experiment to calibrate an inertial balance (that doesn’t need gravity).

Deconstructing a special effect from Star Wars

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.

Build a radio transmitter – mostly from scratch.

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.

The End.

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.

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