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.

MacGyver Season 3 Episode 18 Science Notes: Murdoc + Helman + Hit

I honestly don’t know how I skipped over this episode with my MacGyver science notes. Oh well, let’s finish this up. There aren’t too many hacks in this episode, so this won’t be too long.

One Way Mirror

Murdoc makes a great point. Is it a one way mirror or a two way mirror? The main idea is that Murdoc can’t see through the glass, but the other people can see through to view what Murdoc is doing.

These things aren’t magic. At the most basic level, a “one way mirror” is just a plane of glass. When light hits glass, some of it is reflected and some of it is transmitted. If you are on one side of the glass and there is WAY more reflected light coming back at you than the light transmitted from the other side, then you can’t see that transmitted light. The glass would look like a mirror.

This is exactly what happens when you are inside a house at night with the lights on. The lights reflect too much and there isn’t much light from outside coming in, so you just see a reflection. It would look like this.

If you are outside on a dark night, the opposite is true. You can see INTO the house.

So, for the one way mirror, you need a glass separating two rooms. The dark room is the room with the observers and the light room is where the prisoner sits.

Here is an older post with more details about seeing through windows.

Pulley Skateboard Battering Ram

This is a classic simple machine. The key to all simple machines is that you can make a system that pulls over a greater distance and produces a greater force (or you can do it the opposite of this).

In this case, MacGyver makes a compound pulley. You need two pulleys. If you run the string through these two pulleys, you can make two different distances. The distance one side is pulled is twice the distance of the other side. Here is a diagram.

Yes, that’s a rather crude sketch—I did it fairly quickly. Here is a video that walks through the setup. I mention that there are two ways to set up this skateboard battering ram, this only covers one method.

Here is a much more detailed post on pulleys.

Stopping a Truck with a Truck

MacGyver uses a winch cable to connect their truck to Murdoc’s truck. They then slam on the breaks. So, would this work? Yeah, probably.

Assuming the two vehicles have the same material for the tires, then they would have the same coefficient of friction. A basic model for friction says that the frictional force is proportional to the force the ground pushes up on the object (we call this the normal force).

F_f = \mu N

Since both cars are on flat ground, the normal force is equal to the car’s weight. That means the heavier car would have a greater frictional force. Yes, I’m making some other assumptions about the tires “locking up”—but still, this is plausible.

Even if the frictional force wasn’t enough to stop the truck, the cable is attached to the side of Murdoc’s truck. This side force would rotate the truck and also prevent it from driving straight.

MacGyver Season 3

Here is a list of all of my science notes for season 3

MacGyver Season 2

Here is a collection of all my science notes for Season 2.

Here is the list of notes for Season 1

MacGyver Season 2 Episode 23 Science Notes: MacGyver + MacGyver

It’s funny how the title is sort of a spoiler for the episode. Right?

DIY Safe Cracker

This is technically a MacGyver-hack since it’s from MacGyver, just not from Angus MacGyver.

The basic idea is to open a safe with a dial on it. Instead of trying to figure out the lock combination, a robot can just try EVERY combination. This is called a brute-force hack since it’s not elegant but it works.

Oh, you want to build one of these yourself? You are in luck, here is an epic guide. https://learn.sparkfun.com/tutorials/building-a-safe-cracking-robot

Also, here is another brute force hack (on a key code door).

Book Cipher

I’ll be honest. I had no idea how a book cipher worked. But with a little help from the internet, I finally figured it out. Here’s how it works.

  • You take some text that you want to send. The example I use is the word “cat”—yes, that’s sort of silly.
  • Next, you need to convert each letter to a number. I’m using the ASCII UTF-8 format to convert each letter to a hexadecimal number (base-16 numbers instead of base 10). For “cat” this would be 43 41 54.
  • Now I take a word from my “book”—in this case it’s a take out menu from a Chinese restaurant. If I use SPR (from spring roll), I can also convert that to ASCII to get 53 50 52. This is my key.
  • Now I add my text and my code to get 96 91 A6. REMEMBER these are hex numbers, so you have to add them differently than you would with decimal numbers. This gives me the code—this is what you send.
  • To decode the message, you just do the opposite.

Here is a longer explanation with a video.

Just for fun, here are some of my notes along with Oversight’s calculations on the dashboard.

Fuel Pump

MacGyver needs to transfer fuel from one car to another. Here is a very cool pump.

The key to most of these pumps is a one way valve. You need to make something so that water can flow the way you want to pump, but not the other way. Here is a very simple way to make a one way pump valve with a turkey baster and small ball.

Belt Handcuffs and Bolo

Really not much to say here—normal MacGyver stuff.

Ascender Rig

MacGyver and MacGyver build a device so that they can get on the roof a building. Yes, it’s an ascender rig. It’s basically just a battery (a car battery in this case) and an electric motor. The motor winds up a rope and causes the whole thing to move up.

Here’s the cool part. You could really do this with just about any electric motor. Yes, even that tiny weak motor could still lift two humans. The only difference would be the speed. If you get the gear ratio right, this tiny motor would slowly wind up the rope and just take longer to get to the top.

Spark Gap Generator

The spark gap generator was the first type of radio transmitter. When a spark is created, it also produces electromagnetic waves (over a broad range of frequencies). That means you can’t really have radio channels, but you can indeed send a signal.

If you want to know more about spark gap generators, here is some info. I even built one mostly from scratch.

https://rhettallain.com/2018/12/14/adventures-in-spark-gaps/

But could you make a spark gap generator with a magnetic stirrer? I think so. One of the key things you need is a changing electric current. If you use the spinning stirrer, it can make electrical contacts at different points during the spin. Here is an example.

MacGyver Season 2 Episode 22 Science Notes: UFO + Area 51

NASCAR Physics

Here is a great homework problem for you. What physics or technical advice could MacGyver offer to a professional NASCAR driver to improve the track time? It’s tough, right? I mean—you could say “go faster” or “get a bigger engine” or stuff like that. But haven’t they already thought of the “go faster” strategy? Probably.

How about this? What if there is a significant wind at the track? Let me start my explanation with a diagram. Note: I am just a physicist and not actually a NASCAR expert.

Inline image 2

I incorrectly labeled the turns as “A” and “B”, but let’s call turn B turn 3 instead (like in the show). So, suppose there is a wind coming from the North. That means that in turn 3, there will be more air resistance (going into the wind) than in turn 4 (going with the wind).

In order to decrease the time in turn, the driver could take the inside of the turn. This would mean that the total distance is shorter (because it’s a smaller circle for the inside turn). If you take the outside turn, the car can travel faster but over a longer (slightly) distance.

But with air resistance, you might be able to make a small improvement on time by driving the slower and shorter distance. Yes, it is indeed true that the normal model for the air resistance force is proportional to the square of the relative speed between the car and the air (but air resistance is in fact quite complicated).

Testing an Unknown Object

MacGyver and Riley meet up with a scientist that is trying to identify an unknown object. You might have missed it, but there is a nice list of tests on the board in the background.

I could probably write a whole book about these tests, but let me just point out that density is a great one to start with. The density is the ratio of mass to volume for an object, but it can tell you a lot. Is it hollow? Is it solid? If it’s solid, the density of a material is one way to identify the exact material. Plus it’s a super simple test that wouldn’t destroy the object.

Salt Water Faraday Cage

Yes, this is essentially a Faraday cage. MacGyver covers the sphere with a lab coat soaked in salt water. The salt produces ions that turns the water from an insulator into a conductor. Once you have a conductor around the sphere, then charges can move around to make an electric field that cancels the field in the radiated electromagnetic wave.

One thing about a Faraday cage like this—it doesn’t stop all electromagnetic waves. Since the electric field oscillates back and forth, the charges in the liquid can’t always adjust fast enough. This means that this could block some frequencies of electromagnetic waves—but not others.

Liquid Metal Isn’t Completely Crazy

What the heck is up with this metal that turns into a liquid? Yes, this is partly science fiction—but at least it’s based on some real stuff.

Here is a liquid metal that can form into a shape based on an electric current. https://www.businessinsider.com/liquid-metal-discovery-paves-way-for-shape-shifting-robotse-2015-4

Moving a Wounded Scientist

It’s called a travois—https://en.wikipedia.org/wiki/Travois. The basic version is just a cloth stretched between two sticks. Then you put a person on the sticks and drag it.

For MacGyver’s version, he uses some wheels.

Celestial Navigation

Here is the line that I recommended:

“The idea of celestial navigation is pretty simple—it’s the precision that’s difficult.”

If you want to find out where you are on the Earth, you need to get your longitude and your latitude. Finding your latitude is really quite simple—especially in the Northern hemisphere. If you just measure the angle that the North Star lies above horizon and subtract from 90 degrees, that’s it.

This is essentially the role of a sextant. It’s just a really fancy way of measuring angles. They really aren’t too hard to build, here is one that I made.

What about longitude? That’s a much tougher problem. One way you can find your longitude is by measuring the time of local noon (the time that the Sun is at its highest point) and comparing that to the noon in Greenwich. So, that means you need a very nice clock. In fact, this was the biggest obstacle to overcome for early navigation, the invention of a reliable clock.

Of course MacGyver has a clock. However, he doesn’t have the Sun since it’s at night. One way to solve this problem is the observe the rising time of some known star (other than the Sun) and compare this to that star’s normal position in the sky. Knowing this time could give you your location, but you need to know the celestial coordinates of a star. MacGyver is enough of a nerd (in a good way) that he might have a particular star memorized.

In order to be over prepared for the show, I made a video going over the exact calculations MacGyver might make.

DIY Spot Welder

Yup. You really just need some high voltage and current and you can weld some stuff. Here is something similar to MacGyver’s build using the transformer from a microwave. https://www.instructables.com/id/Build-a-Microwave-Transformer-Homemade-Welder/

Welding Glasses

Don’t try this, but it should work. Those old floppy disks are partially transparent. If you take about the hard part of the disk, the spinning part (where the data is stored) is both easy to cut and could make some welding glasses. https://eclipse.gsfc.nasa.gov/SEhelp/safety2.html

MacGyver Season 2 Episode 21 Science Notes: Wind + Water

Ignite gas with a pay phone.

In order to escape from a dinner, MacGyver opens all the gas outlets in the kitchen to fill the building with gas. He then takes apart a pay phone and disconnects the ringer. Super old pay phones (what’s a pay phone?) have a mechanical oscillator that rings a bell.

Can you use this to make a spark? Oh, yeah. In fact, I used a very similar in a version of my spark gap generator radio transmitter.

Boom crane with a ladder

In order to get some heavy pieces on top of a house (to rebuild the roof), MacGyver uses a rope running over a movable ladder to act as a type of crane. I thought I had a pre-show sketch of this, but I couldn’t find it.

Fixing a flat tire

The truck has a flat tire. MacGyver needs to do two things—plug the hole and fill the tire. To plug the hole, he uses a bit of rubber and heats it up. Then you just push this through the hole in the tire. That’s it. Honestly, I have done this with an actual flat tire and I was surprised that it worked.

For the air, MacGyver connects the tire of the scooter to the truck. Yes, this would add some air to the truck tire from the scooter tire—but only until the two tires reach the same pressure. That might plausibly be enough air to get you going, but likely not.

If you want to get more air from the scooter tire, you could heat it up. When the air in the scooter tire increases in temperature, it increases in pressure. You need the scooter tire pressure higher than the truck tire to get a transfer.

Black pepper on a gunshot wound

One of MacGyver’s friends gets shot in a bank. MacGyver needs to stop the bleeding. Oh, here is some black pepper. Yup, that seems like it would work. https://knowledgeweighsnothing.com/how-to-stop-bleeding-with-black-pepper/

DIY radio

A basic radio really isn’t all that complicated. You need a capacitor, a coil of wire (for the inductor) and some type of diode. Soldiers used to make them from scratch on the front line in WWII—they were called foxhole radios.

Here’s a more detailed post about this simple radio—https://www.wired.com/2016/05/go-ahead-connect-inductor-capacitor-see-happens/

Ok, but what if you want a two way radio? Yup, it’s much more difficult to transmit. But still, you get the idea. Here is a sketch from the show notes.

Dye pack explosion

So these banks have these exploding packs of dye. That way they can toss them in with some money when bad guys steal stuff. Some of the packs are radio activated, but others go off (after a delay) when passing out of the main bank area. https://en.wikipedia.org/wiki/Dye_pack

MacGyver just puts one in a coffee cup and tosses it past the door. Since it makes a noise, the baddie goes to investigate and BOOM. Ink in the face.

Ethernet rope ladder

MacGyver makes a rope ladder out of ethernet cable so that people can escape from a second story window. It might take a while to make, but this is fairly legit.

Bomb thingy

I honestly can’t remember the exact kind of bomb MacGyver is making here—and that’s fine because I wouldn’t tell you anyway. But he uses some stuff from the bank to get into the sewers below.

Falling telephone pole

For the last hack, MacGyver hits a telephone pole that’s ready to fall over anyway. The pole falls and lands on the bad guys car. The end.

MacGyver Season 2 Episode 20 Science Notes: Skyscraper + Power

DIY torch

Hand sanitizer is mostly ethyl alcohol—it burns fairly nicely. Oh, but don’t play with fire. If you put this stuff on a roll of paper towels, it should make a great torch. It would probably have more of a blue color though.

Actually, you can just squirt some hand sanitizer on a cement floor and light it on fire.

WiFi Radar

This is a “Riley hack”. Since the power is out in the building, she hacks into the wifi routers for the nearby buildings. By looking at the strength of the wifi signals that go through the building, she can sort of judge where people are moving.

Oh, this is crazy? No, this is based on some real stuff.

https://gizmodo.com/scientists-are-turning-wifi-routers-into-creepy-radar-c-1794961990

DIY Glow stick

That glow stick that you use for Halloween is just a mixture of two chemicals. In that particular chemical reaction, it is an example of chemiluminescent—a chemical reaction that produces light. It’s sort of cool.

It’s not perfect, but it is possible to make your own glowstick.

Elevator descender

You can’t really see exactly what MacGyver has rigged up—but it’s a type of descender. The basic idea is that when a torque is applied to a ring around a line, it binds up with a frictional force to prevent it from sliding.

Here is a diagram I created that might help explain how this would work.

Inline image 1

These two loops around the elevator cable could be just about anything. One idea was to use some padlocks—but as long as it’s stiff and goes around the cable, that’s fine.

So, here’s how it works.

  • If MacGyver puts his weight on the bottom element, it will provide a torque and bind up against the cable.
  • He can then move the top element down.
  • Next, he hang from the top element so it binds and then he can move the bottom thing.
  • Repeat

DIY Tesla coil

A Tesla coil is essentially a device to create a very large electric potential difference (many would say high voltage). The most common method is to use a series of transformers—a way to convert AC signals to higher voltage (yes, I said it).

For MacGyver’s hack, he uses the ballast from a bunch of fluorescent lights. A fluorescent light starts with a tube of gas. Electrons are accelerated in this tube and interact with the gas molecules to produce light. This light is in the ultraviolet range, so you really can’t see it. But there is a coating on the inside of the tube that absorbs the UV and produces white light—this is the “fluorescence” part of a fluorescent light.

But the key is high voltage. Yes, the electrons need to be accelerated over an electric potential difference that is greater than the usual 120 volts from your AC outlet. That’s where the ballast comes into play. This takes the 120 volts from your household circuit and ramps it up to something like 500 volts.

What about a Tesla coil? If you want to get cool (and giant) sparks, you will need about 5,000-30,000 volts. So, would 10 ballasts do the trick? Probably not—the voltages just don’t add up that way. But still, it’s based on a real thing.

Faraday cage

You can’t “block” electric fields that are associated with things like sparks and electromagnetic waves—but you can make more electric fields that produce a zero electric field. That’s what a Faraday cage does. It creates more electric fields that cancel an external electric field.

Here is a very basic example. Suppose I have a constant electric field and I want to “block” this. If I put a piece of metal around me, the external electric field will move charges in the metal and these charges will create more electric fields. When you add all the fields up, you get a zero field—it’s just like the field is canceled.

The cool part about a Faraday cage is that it doesn’t even have to be solid metal. You can still have holes in it and it will cancel electric fields. Here is an example of a Faraday cage with a radio and some aluminum foil.

MacGyver Season 2 Episode 19 Science Notes: Benjamin Franklin + Grey Duffle

Homemade Balloon Float

This is just the beginning of the show, so we don’t really know what’s going on except that Riley, Jack and MacGyver are on a trampoline supported by a bunch of balloons.

So, I will just leave this as a homework question for you. How many balloons would you need to lift 3 humans?

Resonance

Pinned down by gunfire, MacGyver needs a way to distract the baddies so that they can make their move. Angus takes his phone and plugs into an audio sound system and plays some high pitched song. This is the classic demo of singing to break some glass. Of course, that doesn’t usually involve a glass window—but still this is all about resonance.

If you go out to a playground, you can find a nice swing. If you push the swing at regular intervals, you can get the swing amplitude to increase. But here is the key point. The frequency of the pushes has to be the same as the natural oscillation frequency of the swing. Otherwise, your push might be timed at the bottom of the swinging motion which could cause the thing to slow down.

If you want to break glass with sound, it is indeed possible. Here’s what you do. Take some glass and give it a nice little tap so that it makes a ringing tone. Measure the frequency of this ring and then play that same frequency with a speaker—it’s got to be LOUD for it to work.

Of course loud noises and breaking glasses aren’t always safe. Here is an alternative demonstration with resonance. As a bonus, you can use this as a magic trick for your friends.

Detecting counterfeit money

They have all these 100 dollar bills. The suspicion is that they are fake—they are one dollar bills reprinted to be 100s. MacGyver puts them in an acid solution to dissolve the new ink as a test.

GPS phone tracker

MacGyver takes the gps receiver along with a battery from a phone and creates a tracking device. Of course the gps is actually built into the processor for most phones—so let’s just say he takes that whole thing (along with the LTE transmitter). Yeah, this would basically work.

Duffle bag battering ram

There is a duffle bag filled with cash. MacGyver hangs this up and uses it as a type of battering ram—to knock over a bad guy.

Bonus Homework

When MacGyver brings in the counterfeit money, he says:

“Yeah, well one million dollars in 100 dollar bills is actually only 20 pounds…so…”

OK—go. Check if this quote is legit. Here is some help. This is a post to estimate the size of a stack that contains 1 trillion dollars. I also use this as an opportunity to calculate the density for a dollar bill. https://www.wired.com/2011/09/stacking-one-trillion-dollars/

MacGyver Season 2 Episode 18 Science Notes: Riley + Airplane

Carpet body restraint

There’s really not too much to explain here. MacGyver rolls a guy up in a carpet and uses that to keep him in place. Seems like this should work.

Reminder—even though there’s not any great science to talk about here, I love these kinds of hacks.

Pick a lock with an antenna

MacGyver pulls a metal antenna off a motorcycle and then uses it to pick the lock on the same motorcycle. Oh, this is a police motorcycle—he uses it to turn on the siren.

Is this possible? Possible, yes. Normally you need two things to pick a lock—something to move the lock pins and something to provide torque. Theoretically, you could do it with one—but it would be tough.

Radiator fire extinguisher

There’s a car on fire and they need to get something out of it. MacGyver improvises a DIY fire extinguisher by using the cooling system of another car. He grabs a pipe and then pokes a hole in the radiator. When the engine is revved up, the coolant shoots out through the pipe and onto the burning car.

Again, the theory here is solid. You could probably even get the coolant to shoot fairly far. However, it would take a significant amount of coolant to put out a fire.

Statue battering ram

This one is good. MacGyver and Jack take a marble statue and support it from some rope and stuff such that it can swing. Then they swing this statue into a door. Boom—battering ram.

Hacking airplane wifi

OK, not hacking to get free wifi but using the wifi to control the whole plane. That’s what Riley does as she is stuck on a plane with a virus. Is this even possible?

Sadly, this might be true. Check this out. https://www.wired.com/2015/05/possible-passengers-hack-commercial-aircraft/